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* [patch V3 00/20] Lock ordering documentation and annotation for lockdep
@ 2020-03-21 11:25 Thomas Gleixner
  2020-03-21 11:25 ` [patch V3 01/20] PCI/switchtec: Fix init_completion race condition with poll_wait() Thomas Gleixner
                   ` (20 more replies)
  0 siblings, 21 replies; 38+ messages in thread
From: Thomas Gleixner @ 2020-03-21 11:25 UTC (permalink / raw)
  To: LKML
  Cc: Peter Zijlstra, Ingo Molnar, Sebastian Siewior, Linus Torvalds,
	Joel Fernandes, Oleg Nesterov, Davidlohr Bueso, Logan Gunthorpe,
	Bjorn Helgaas, Kurt Schwemmer, linux-pci, Greg Kroah-Hartman,
	Felipe Balbi, linux-usb, Kalle Valo, David S. Miller,
	linux-wireless, netdev, Darren Hart, Andy Shevchenko,
	platform-driver-x86, Zhang Rui, Rafael J. Wysocki, linux-pm,
	Len Brown, linux-acpi, kbuild test robot, Nick Hu, Greentime Hu,
	Vincent Chen, Guo Ren, linux-csky, Brian Cain, linux-hexagon,
	Tony Luck, Fenghua Yu, linux-ia64, Michal Simek,
	Michael Ellerman, Arnd Bergmann, Geoff Levand, linuxppc-dev,
	Paul E . McKenney, Jonathan Corbet, Randy Dunlap,
	Davidlohr Bueso

This is the third and hopefully final version of this work. The second one
can be found here:

   https://lore.kernel.org/r/20200318204302.693307984@linutronix.de

Changes since V2:

  - Included the arch/XXX fixups for the rcuwait changes (Sebastian)

  - Folded the init fix for the PS3 change (Sebastian)

  - Addressed feedback on documentation (Paul, Davidlohr, Jonathan)

  - Picked up acks and reviewed tags

Thanks,

	tglx


^ permalink raw reply	[flat|nested] 38+ messages in thread

* [patch V3 01/20] PCI/switchtec: Fix init_completion race condition with poll_wait()
  2020-03-21 11:25 [patch V3 00/20] Lock ordering documentation and annotation for lockdep Thomas Gleixner
@ 2020-03-21 11:25 ` Thomas Gleixner
  2020-03-21 11:25 ` [patch V3 02/20] pci/switchtec: Replace completion wait queue usage for poll Thomas Gleixner
                   ` (19 subsequent siblings)
  20 siblings, 0 replies; 38+ messages in thread
From: Thomas Gleixner @ 2020-03-21 11:25 UTC (permalink / raw)
  To: LKML
  Cc: Peter Zijlstra, Ingo Molnar, Sebastian Siewior, Linus Torvalds,
	Joel Fernandes, Oleg Nesterov, Davidlohr Bueso, Logan Gunthorpe,
	Bjorn Helgaas, Kurt Schwemmer, linux-pci, Greg Kroah-Hartman,
	Felipe Balbi, linux-usb, Kalle Valo, David S. Miller,
	linux-wireless, netdev, Darren Hart, Andy Shevchenko,
	platform-driver-x86, Zhang Rui, Rafael J. Wysocki, linux-pm,
	Len Brown, linux-acpi, kbuild test robot, Nick Hu, Greentime Hu,
	Vincent Chen, Guo Ren, linux-csky, Brian Cain, linux-hexagon,
	Tony Luck, Fenghua Yu, linux-ia64, Michal Simek,
	Michael Ellerman, Arnd Bergmann, Geoff Levand, linuxppc-dev,
	Paul E . McKenney, Jonathan Corbet, Randy Dunlap,
	Davidlohr Bueso

From: Logan Gunthorpe <logang@deltatee.com>

The call to init_completion() in mrpc_queue_cmd() can theoretically
race with the call to poll_wait() in switchtec_dev_poll().

  poll()			write()
    switchtec_dev_poll()   	  switchtec_dev_write()
      poll_wait(&s->comp.wait);      mrpc_queue_cmd()
			               init_completion(&s->comp)
				         init_waitqueue_head(&s->comp.wait)

To my knowledge, no one has hit this bug.

Fix this by using reinit_completion() instead of init_completion() in
mrpc_queue_cmd().

Fixes: 080b47def5e5 ("MicroSemi Switchtec management interface driver")
Reported-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Bjorn Helgaas <bhelgaas@google.com>
Cc: Kurt Schwemmer <kurt.schwemmer@microsemi.com>
Cc: linux-pci@vger.kernel.org
Link: https://lkml.kernel.org/r/20200313183608.2646-1-logang@deltatee.com

---
 drivers/pci/switch/switchtec.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/pci/switch/switchtec.c b/drivers/pci/switch/switchtec.c
index a823b4b8ef8a..81dc7ac01381 100644
--- a/drivers/pci/switch/switchtec.c
+++ b/drivers/pci/switch/switchtec.c
@@ -175,7 +175,7 @@ static int mrpc_queue_cmd(struct switchtec_user *stuser)
 	kref_get(&stuser->kref);
 	stuser->read_len = sizeof(stuser->data);
 	stuser_set_state(stuser, MRPC_QUEUED);
-	init_completion(&stuser->comp);
+	reinit_completion(&stuser->comp);
 	list_add_tail(&stuser->list, &stdev->mrpc_queue);
 
 	mrpc_cmd_submit(stdev);
-- 
2.20.1




^ permalink raw reply	[flat|nested] 38+ messages in thread

* [patch V3 02/20] pci/switchtec: Replace completion wait queue usage for poll
  2020-03-21 11:25 [patch V3 00/20] Lock ordering documentation and annotation for lockdep Thomas Gleixner
  2020-03-21 11:25 ` [patch V3 01/20] PCI/switchtec: Fix init_completion race condition with poll_wait() Thomas Gleixner
@ 2020-03-21 11:25 ` Thomas Gleixner
  2020-03-21 11:25 ` [patch V3 03/20] usb: gadget: Use completion interface instead of open coding it Thomas Gleixner
                   ` (18 subsequent siblings)
  20 siblings, 0 replies; 38+ messages in thread
From: Thomas Gleixner @ 2020-03-21 11:25 UTC (permalink / raw)
  To: LKML
  Cc: Peter Zijlstra, Ingo Molnar, Sebastian Siewior, Linus Torvalds,
	Joel Fernandes, Oleg Nesterov, Davidlohr Bueso, Logan Gunthorpe,
	Bjorn Helgaas, Kurt Schwemmer, linux-pci, Greg Kroah-Hartman,
	Felipe Balbi, linux-usb, Kalle Valo, David S. Miller,
	linux-wireless, netdev, Darren Hart, Andy Shevchenko,
	platform-driver-x86, Zhang Rui, Rafael J. Wysocki, linux-pm,
	Len Brown, linux-acpi, kbuild test robot, Nick Hu, Greentime Hu,
	Vincent Chen, Guo Ren, linux-csky, Brian Cain, linux-hexagon,
	Tony Luck, Fenghua Yu, linux-ia64, Michal Simek,
	Michael Ellerman, Arnd Bergmann, Geoff Levand, linuxppc-dev,
	Paul E . McKenney, Jonathan Corbet, Randy Dunlap,
	Davidlohr Bueso

From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

The poll callback is using the completion wait queue and sticks it into
poll_wait() to wake up pollers after a command has completed.

This works to some extent, but cannot provide EPOLLEXCLUSIVE support
because the waker side uses complete_all() which unconditionally wakes up
all waiters. complete_all() is required because completions internally use
exclusive wait and complete() only wakes up one waiter by default.

This mixes conceptually different mechanisms and relies on internal
implementation details of completions, which in turn puts contraints on
changing the internal implementation of completions.

Replace it with a regular wait queue and store the state in struct
switchtec_user.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Logan Gunthorpe <logang@deltatee.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Bjorn Helgaas <bhelgaas@google.com>
Cc: Kurt Schwemmer <kurt.schwemmer@microsemi.com>
Cc: linux-pci@vger.kernel.org
---
V2: Reworded changelog.
---
 drivers/pci/switch/switchtec.c |   22 +++++++++++++---------
 1 file changed, 13 insertions(+), 9 deletions(-)

--- a/drivers/pci/switch/switchtec.c
+++ b/drivers/pci/switch/switchtec.c
@@ -52,10 +52,11 @@ struct switchtec_user {
 
 	enum mrpc_state state;
 
-	struct completion comp;
+	wait_queue_head_t cmd_comp;
 	struct kref kref;
 	struct list_head list;
 
+	bool cmd_done;
 	u32 cmd;
 	u32 status;
 	u32 return_code;
@@ -77,7 +78,7 @@ static struct switchtec_user *stuser_cre
 	stuser->stdev = stdev;
 	kref_init(&stuser->kref);
 	INIT_LIST_HEAD(&stuser->list);
-	init_completion(&stuser->comp);
+	init_waitqueue_head(&stuser->cmd_comp);
 	stuser->event_cnt = atomic_read(&stdev->event_cnt);
 
 	dev_dbg(&stdev->dev, "%s: %p\n", __func__, stuser);
@@ -175,7 +176,7 @@ static int mrpc_queue_cmd(struct switcht
 	kref_get(&stuser->kref);
 	stuser->read_len = sizeof(stuser->data);
 	stuser_set_state(stuser, MRPC_QUEUED);
-	reinit_completion(&stuser->comp);
+	stuser->cmd_done = false;
 	list_add_tail(&stuser->list, &stdev->mrpc_queue);
 
 	mrpc_cmd_submit(stdev);
@@ -222,7 +223,8 @@ static void mrpc_complete_cmd(struct swi
 		memcpy_fromio(stuser->data, &stdev->mmio_mrpc->output_data,
 			      stuser->read_len);
 out:
-	complete_all(&stuser->comp);
+	stuser->cmd_done = true;
+	wake_up_interruptible(&stuser->cmd_comp);
 	list_del_init(&stuser->list);
 	stuser_put(stuser);
 	stdev->mrpc_busy = 0;
@@ -529,10 +531,11 @@ static ssize_t switchtec_dev_read(struct
 	mutex_unlock(&stdev->mrpc_mutex);
 
 	if (filp->f_flags & O_NONBLOCK) {
-		if (!try_wait_for_completion(&stuser->comp))
+		if (!stuser->cmd_done)
 			return -EAGAIN;
 	} else {
-		rc = wait_for_completion_interruptible(&stuser->comp);
+		rc = wait_event_interruptible(stuser->cmd_comp,
+					      stuser->cmd_done);
 		if (rc < 0)
 			return rc;
 	}
@@ -580,7 +583,7 @@ static __poll_t switchtec_dev_poll(struc
 	struct switchtec_dev *stdev = stuser->stdev;
 	__poll_t ret = 0;
 
-	poll_wait(filp, &stuser->comp.wait, wait);
+	poll_wait(filp, &stuser->cmd_comp, wait);
 	poll_wait(filp, &stdev->event_wq, wait);
 
 	if (lock_mutex_and_test_alive(stdev))
@@ -588,7 +591,7 @@ static __poll_t switchtec_dev_poll(struc
 
 	mutex_unlock(&stdev->mrpc_mutex);
 
-	if (try_wait_for_completion(&stuser->comp))
+	if (stuser->cmd_done)
 		ret |= EPOLLIN | EPOLLRDNORM;
 
 	if (stuser->event_cnt != atomic_read(&stdev->event_cnt))
@@ -1272,7 +1275,8 @@ static void stdev_kill(struct switchtec_
 
 	/* Wake up and kill any users waiting on an MRPC request */
 	list_for_each_entry_safe(stuser, tmpuser, &stdev->mrpc_queue, list) {
-		complete_all(&stuser->comp);
+		stuser->cmd_done = true;
+		wake_up_interruptible(&stuser->cmd_comp);
 		list_del_init(&stuser->list);
 		stuser_put(stuser);
 	}



^ permalink raw reply	[flat|nested] 38+ messages in thread

* [patch V3 03/20] usb: gadget: Use completion interface instead of open coding it
  2020-03-21 11:25 [patch V3 00/20] Lock ordering documentation and annotation for lockdep Thomas Gleixner
  2020-03-21 11:25 ` [patch V3 01/20] PCI/switchtec: Fix init_completion race condition with poll_wait() Thomas Gleixner
  2020-03-21 11:25 ` [patch V3 02/20] pci/switchtec: Replace completion wait queue usage for poll Thomas Gleixner
@ 2020-03-21 11:25 ` Thomas Gleixner
  2020-03-25  8:37   ` Felipe Balbi
  2020-03-21 11:25 ` [patch V3 04/20] orinoco_usb: Use the regular completion interfaces Thomas Gleixner
                   ` (17 subsequent siblings)
  20 siblings, 1 reply; 38+ messages in thread
From: Thomas Gleixner @ 2020-03-21 11:25 UTC (permalink / raw)
  To: LKML
  Cc: Peter Zijlstra, Ingo Molnar, Sebastian Siewior, Linus Torvalds,
	Joel Fernandes, Oleg Nesterov, Davidlohr Bueso,
	Greg Kroah-Hartman, Felipe Balbi, linux-usb, Logan Gunthorpe,
	Bjorn Helgaas, Kurt Schwemmer, linux-pci, Kalle Valo,
	David S. Miller, linux-wireless, netdev, Darren Hart,
	Andy Shevchenko, platform-driver-x86, Zhang Rui,
	Rafael J. Wysocki, linux-pm, Len Brown, linux-acpi,
	kbuild test robot, Nick Hu, Greentime Hu, Vincent Chen, Guo Ren,
	linux-csky, Brian Cain, linux-hexagon, Tony Luck, Fenghua Yu,
	linux-ia64, Michal Simek, Michael Ellerman, Arnd Bergmann,
	Geoff Levand, linuxppc-dev, Paul E . McKenney, Jonathan Corbet,
	Randy Dunlap, Davidlohr Bueso

From: Thomas Gleixner <tglx@linutronix.de>

ep_io() uses a completion on stack and open codes the waiting with:

  wait_event_interruptible (done.wait, done.done);
and
  wait_event (done.wait, done.done);

This waits in non-exclusive mode for complete(), but there is no reason to
do so because the completion can only be waited for by the task itself and
complete() wakes exactly one exlusive waiter.

Replace the open coded implementation with the corresponding
wait_for_completion*() functions.

No functional change.

Reported-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Felipe Balbi <balbi@kernel.org>
Cc: linux-usb@vger.kernel.org
---
V2: New patch to avoid the conversion to swait interfaces later
---
 drivers/usb/gadget/legacy/inode.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/drivers/usb/gadget/legacy/inode.c
+++ b/drivers/usb/gadget/legacy/inode.c
@@ -344,7 +344,7 @@ ep_io (struct ep_data *epdata, void *buf
 	spin_unlock_irq (&epdata->dev->lock);
 
 	if (likely (value == 0)) {
-		value = wait_event_interruptible (done.wait, done.done);
+		value = wait_for_completion_interruptible(&done);
 		if (value != 0) {
 			spin_lock_irq (&epdata->dev->lock);
 			if (likely (epdata->ep != NULL)) {
@@ -353,7 +353,7 @@ ep_io (struct ep_data *epdata, void *buf
 				usb_ep_dequeue (epdata->ep, epdata->req);
 				spin_unlock_irq (&epdata->dev->lock);
 
-				wait_event (done.wait, done.done);
+				wait_for_completion(&done);
 				if (epdata->status == -ECONNRESET)
 					epdata->status = -EINTR;
 			} else {



^ permalink raw reply	[flat|nested] 38+ messages in thread

* [patch V3 04/20] orinoco_usb: Use the regular completion interfaces
  2020-03-21 11:25 [patch V3 00/20] Lock ordering documentation and annotation for lockdep Thomas Gleixner
                   ` (2 preceding siblings ...)
  2020-03-21 11:25 ` [patch V3 03/20] usb: gadget: Use completion interface instead of open coding it Thomas Gleixner
@ 2020-03-21 11:25 ` Thomas Gleixner
  2020-03-21 11:25 ` [patch V3 05/20] acpi: Remove header dependency Thomas Gleixner
                   ` (16 subsequent siblings)
  20 siblings, 0 replies; 38+ messages in thread
From: Thomas Gleixner @ 2020-03-21 11:25 UTC (permalink / raw)
  To: LKML
  Cc: Peter Zijlstra, Ingo Molnar, Sebastian Siewior, Linus Torvalds,
	Joel Fernandes, Oleg Nesterov, Davidlohr Bueso,
	Greg Kroah-Hartman, Kalle Valo, David S. Miller, linux-wireless,
	netdev, linux-usb, Logan Gunthorpe, Bjorn Helgaas,
	Kurt Schwemmer, linux-pci, Felipe Balbi, Darren Hart,
	Andy Shevchenko, platform-driver-x86, Zhang Rui,
	Rafael J. Wysocki, linux-pm, Len Brown, linux-acpi,
	kbuild test robot, Nick Hu, Greentime Hu, Vincent Chen, Guo Ren,
	linux-csky, Brian Cain, linux-hexagon, Tony Luck, Fenghua Yu,
	linux-ia64, Michal Simek, Michael Ellerman, Arnd Bergmann,
	Geoff Levand, linuxppc-dev, Paul E . McKenney, Jonathan Corbet,
	Randy Dunlap, Davidlohr Bueso

From: Thomas Gleixner <tglx@linutronix.de>

The completion usage in this driver is interesting:

  - it uses a magic complete function which according to the comment was
    implemented by invoking complete() four times in a row because
    complete_all() was not exported at that time.

  - it uses an open coded wait/poll which checks completion:done. Only one wait
    side (device removal) uses the regular wait_for_completion() interface.

The rationale behind this is to prevent that wait_for_completion() consumes
completion::done which would prevent that all waiters are woken. This is not
necessary with complete_all() as that sets completion::done to UINT_MAX which
is left unmodified by the woken waiters.

Replace the magic complete function with complete_all() and convert the
open coded wait/poll to regular completion interfaces.

This changes the wait to exclusive wait mode. But that does not make any
difference because the wakers use complete_all() which ignores the
exclusive mode.

Reported-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Kalle Valo <kvalo@codeaurora.org>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: linux-wireless@vger.kernel.org
Cc: netdev@vger.kernel.org
Cc: linux-usb@vger.kernel.org
---
V2: New patch to avoid conversion to swait functions later.
---
 drivers/net/wireless/intersil/orinoco/orinoco_usb.c |   21 ++++----------------
 1 file changed, 5 insertions(+), 16 deletions(-)

--- a/drivers/net/wireless/intersil/orinoco/orinoco_usb.c
+++ b/drivers/net/wireless/intersil/orinoco/orinoco_usb.c
@@ -365,17 +365,6 @@ static struct request_context *ezusb_all
 	return ctx;
 }
 
-
-/* Hopefully the real complete_all will soon be exported, in the mean
- * while this should work. */
-static inline void ezusb_complete_all(struct completion *comp)
-{
-	complete(comp);
-	complete(comp);
-	complete(comp);
-	complete(comp);
-}
-
 static void ezusb_ctx_complete(struct request_context *ctx)
 {
 	struct ezusb_priv *upriv = ctx->upriv;
@@ -409,7 +398,7 @@ static void ezusb_ctx_complete(struct re
 
 			netif_wake_queue(dev);
 		}
-		ezusb_complete_all(&ctx->done);
+		complete_all(&ctx->done);
 		ezusb_request_context_put(ctx);
 		break;
 
@@ -419,7 +408,7 @@ static void ezusb_ctx_complete(struct re
 			/* This is normal, as all request contexts get flushed
 			 * when the device is disconnected */
 			err("Called, CTX not terminating, but device gone");
-			ezusb_complete_all(&ctx->done);
+			complete_all(&ctx->done);
 			ezusb_request_context_put(ctx);
 			break;
 		}
@@ -690,11 +679,11 @@ static void ezusb_req_ctx_wait(struct ez
 			 * get the chance to run themselves. So we make sure
 			 * that we don't sleep for ever */
 			int msecs = DEF_TIMEOUT * (1000 / HZ);
-			while (!ctx->done.done && msecs--)
+
+			while (!try_wait_for_completion(&ctx->done) && msecs--)
 				udelay(1000);
 		} else {
-			wait_event_interruptible(ctx->done.wait,
-						 ctx->done.done);
+			wait_for_completion(&ctx->done);
 		}
 		break;
 	default:



^ permalink raw reply	[flat|nested] 38+ messages in thread

* [patch V3 05/20] acpi: Remove header dependency
  2020-03-21 11:25 [patch V3 00/20] Lock ordering documentation and annotation for lockdep Thomas Gleixner
                   ` (3 preceding siblings ...)
  2020-03-21 11:25 ` [patch V3 04/20] orinoco_usb: Use the regular completion interfaces Thomas Gleixner
@ 2020-03-21 11:25 ` Thomas Gleixner
  2020-03-21 11:25 ` [patch V3 06/20] nds32: Remove mm.h from asm/uaccess.h Thomas Gleixner
                   ` (15 subsequent siblings)
  20 siblings, 0 replies; 38+ messages in thread
From: Thomas Gleixner @ 2020-03-21 11:25 UTC (permalink / raw)
  To: LKML
  Cc: Peter Zijlstra, Ingo Molnar, Sebastian Siewior, Linus Torvalds,
	Joel Fernandes, Oleg Nesterov, Davidlohr Bueso, Darren Hart,
	Andy Shevchenko, platform-driver-x86, Greg Kroah-Hartman,
	Zhang Rui, Rafael J. Wysocki, linux-pm, Len Brown, linux-acpi,
	Logan Gunthorpe, Bjorn Helgaas, Kurt Schwemmer, linux-pci,
	Felipe Balbi, linux-usb, Kalle Valo, David S. Miller,
	linux-wireless, netdev, kbuild test robot, Nick Hu, Greentime Hu,
	Vincent Chen, Guo Ren, linux-csky, Brian Cain, linux-hexagon,
	Tony Luck, Fenghua Yu, linux-ia64, Michal Simek,
	Michael Ellerman, Arnd Bergmann, Geoff Levand, linuxppc-dev,
	Paul E . McKenney, Jonathan Corbet, Randy Dunlap,
	Davidlohr Bueso

From: Peter Zijlstra <peterz@infradead.org>

In order to avoid future header hell, remove the inclusion of
proc_fs.h from acpi_bus.h. All it needs is a forward declaration of a
struct.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Darren Hart <dvhart@infradead.org>
Cc: Andy Shevchenko <andy@infradead.org>
Cc: platform-driver-x86@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Zhang Rui <rui.zhang@intel.com>
Cc: "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>
Cc: linux-pm@vger.kernel.org
Cc: Len Brown <lenb@kernel.org>
Cc: linux-acpi@vger.kernel.org
---
 drivers/platform/x86/dell-smo8800.c                      |    1 +
 drivers/platform/x86/wmi.c                               |    1 +
 drivers/thermal/intel/int340x_thermal/acpi_thermal_rel.c |    1 +
 include/acpi/acpi_bus.h                                  |    2 +-
 4 files changed, 4 insertions(+), 1 deletion(-)

--- a/drivers/platform/x86/dell-smo8800.c
+++ b/drivers/platform/x86/dell-smo8800.c
@@ -16,6 +16,7 @@
 #include <linux/interrupt.h>
 #include <linux/miscdevice.h>
 #include <linux/uaccess.h>
+#include <linux/fs.h>
 
 struct smo8800_device {
 	u32 irq;                     /* acpi device irq */
--- a/drivers/platform/x86/wmi.c
+++ b/drivers/platform/x86/wmi.c
@@ -29,6 +29,7 @@
 #include <linux/uaccess.h>
 #include <linux/uuid.h>
 #include <linux/wmi.h>
+#include <linux/fs.h>
 #include <uapi/linux/wmi.h>
 
 ACPI_MODULE_NAME("wmi");
--- a/drivers/thermal/intel/int340x_thermal/acpi_thermal_rel.c
+++ b/drivers/thermal/intel/int340x_thermal/acpi_thermal_rel.c
@@ -19,6 +19,7 @@
 #include <linux/acpi.h>
 #include <linux/uaccess.h>
 #include <linux/miscdevice.h>
+#include <linux/fs.h>
 #include "acpi_thermal_rel.h"
 
 static acpi_handle acpi_thermal_rel_handle;
--- a/include/acpi/acpi_bus.h
+++ b/include/acpi/acpi_bus.h
@@ -80,7 +80,7 @@ bool acpi_dev_present(const char *hid, c
 
 #ifdef CONFIG_ACPI
 
-#include <linux/proc_fs.h>
+struct proc_dir_entry;
 
 #define ACPI_BUS_FILE_ROOT	"acpi"
 extern struct proc_dir_entry *acpi_root_dir;



^ permalink raw reply	[flat|nested] 38+ messages in thread

* [patch V3 06/20] nds32: Remove mm.h from asm/uaccess.h
  2020-03-21 11:25 [patch V3 00/20] Lock ordering documentation and annotation for lockdep Thomas Gleixner
                   ` (4 preceding siblings ...)
  2020-03-21 11:25 ` [patch V3 05/20] acpi: Remove header dependency Thomas Gleixner
@ 2020-03-21 11:25 ` Thomas Gleixner
  2020-03-21 11:25 ` [patch V3 07/20] csky: " Thomas Gleixner
                   ` (14 subsequent siblings)
  20 siblings, 0 replies; 38+ messages in thread
From: Thomas Gleixner @ 2020-03-21 11:25 UTC (permalink / raw)
  To: LKML
  Cc: Peter Zijlstra, Ingo Molnar, Sebastian Siewior, Linus Torvalds,
	Joel Fernandes, Oleg Nesterov, Davidlohr Bueso,
	kbuild test robot, Nick Hu, Greentime Hu, Vincent Chen,
	Logan Gunthorpe, Bjorn Helgaas, Kurt Schwemmer, linux-pci,
	Greg Kroah-Hartman, Felipe Balbi, linux-usb, Kalle Valo,
	David S. Miller, linux-wireless, netdev, Darren Hart,
	Andy Shevchenko, platform-driver-x86, Zhang Rui,
	Rafael J. Wysocki, linux-pm, Len Brown, linux-acpi, Guo Ren,
	linux-csky, Brian Cain, linux-hexagon, Tony Luck, Fenghua Yu,
	linux-ia64, Michal Simek, Michael Ellerman, Arnd Bergmann,
	Geoff Levand, linuxppc-dev, Paul E . McKenney, Jonathan Corbet,
	Randy Dunlap, Davidlohr Bueso

From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

The defconfig compiles without linux/mm.h. With mm.h included the
include chain leands to:
|   CC      kernel/locking/percpu-rwsem.o
| In file included from include/linux/huge_mm.h:8,
|                  from include/linux/mm.h:567,
|                  from arch/nds32/include/asm/uaccess.h:,
|                  from include/linux/uaccess.h:11,
|                  from include/linux/sched/task.h:11,
|                  from include/linux/sched/signal.h:9,
|                  from include/linux/rcuwait.h:6,
|                  from include/linux/percpu-rwsem.h:8,
|                  from kernel/locking/percpu-rwsem.c:6:
| include/linux/fs.h:1422:29: error: array type has incomplete element type 'struct percpu_rw_semaphore'
|  1422 |  struct percpu_rw_semaphore rw_sem[SB_FREEZE_LEVELS];

once rcuwait.h includes linux/sched/signal.h.

Remove the linux/mm.h include.

Reported-by: kbuild test robot <lkp@intel.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Nick Hu <nickhu@andestech.com>
Cc: Greentime Hu <green.hu@gmail.com>
Cc: Vincent Chen <deanbo422@gmail.com>
---
V3: New patch
---
 arch/nds32/include/asm/uaccess.h | 1 -
 1 file changed, 1 deletion(-)

diff --git a/arch/nds32/include/asm/uaccess.h b/arch/nds32/include/asm/uaccess.h
index 8916ad9f9f139..3a9219f53ee0d 100644
--- a/arch/nds32/include/asm/uaccess.h
+++ b/arch/nds32/include/asm/uaccess.h
@@ -11,7 +11,6 @@
 #include <asm/errno.h>
 #include <asm/memory.h>
 #include <asm/types.h>
-#include <linux/mm.h>
 
 #define __asmeq(x, y)  ".ifnc " x "," y " ; .err ; .endif\n\t"
 
-- 
2.26.0.rc2



^ permalink raw reply	[flat|nested] 38+ messages in thread

* [patch V3 07/20] csky: Remove mm.h from asm/uaccess.h
  2020-03-21 11:25 [patch V3 00/20] Lock ordering documentation and annotation for lockdep Thomas Gleixner
                   ` (5 preceding siblings ...)
  2020-03-21 11:25 ` [patch V3 06/20] nds32: Remove mm.h from asm/uaccess.h Thomas Gleixner
@ 2020-03-21 11:25 ` " Thomas Gleixner
  2020-03-21 11:25 ` [patch V3 08/20] hexagon: " Thomas Gleixner
                   ` (13 subsequent siblings)
  20 siblings, 0 replies; 38+ messages in thread
From: Thomas Gleixner @ 2020-03-21 11:25 UTC (permalink / raw)
  To: LKML
  Cc: Peter Zijlstra, Ingo Molnar, Sebastian Siewior, Linus Torvalds,
	Joel Fernandes, Oleg Nesterov, Davidlohr Bueso,
	kbuild test robot, Guo Ren, linux-csky, Logan Gunthorpe,
	Bjorn Helgaas, Kurt Schwemmer, linux-pci, Greg Kroah-Hartman,
	Felipe Balbi, linux-usb, Kalle Valo, David S. Miller,
	linux-wireless, netdev, Darren Hart, Andy Shevchenko,
	platform-driver-x86, Zhang Rui, Rafael J. Wysocki, linux-pm,
	Len Brown, linux-acpi, Nick Hu, Greentime Hu, Vincent Chen,
	Brian Cain, linux-hexagon, Tony Luck, Fenghua Yu, linux-ia64,
	Michal Simek, Michael Ellerman, Arnd Bergmann, Geoff Levand,
	linuxppc-dev, Paul E . McKenney, Jonathan Corbet, Randy Dunlap,
	Davidlohr Bueso

From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

The defconfig compiles without linux/mm.h. With mm.h included the
include chain leands to:
|   CC      kernel/locking/percpu-rwsem.o
| In file included from include/linux/huge_mm.h:8,
|                  from include/linux/mm.h:567,
|                  from arch/csky/include/asm/uaccess.h:,
|                  from include/linux/uaccess.h:11,
|                  from include/linux/sched/task.h:11,
|                  from include/linux/sched/signal.h:9,
|                  from include/linux/rcuwait.h:6,
|                  from include/linux/percpu-rwsem.h:8,
|                  from kernel/locking/percpu-rwsem.c:6:
| include/linux/fs.h:1422:29: error: array type has incomplete element type 'struct percpu_rw_semaphore'
|  1422 |  struct percpu_rw_semaphore rw_sem[SB_FREEZE_LEVELS];

once rcuwait.h includes linux/sched/signal.h.

Remove the linux/mm.h include.

Reported-by: kbuild test robot <lkp@intel.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Guo Ren <guoren@kernel.org>
Cc: linux-csky@vger.kernel.org
---
V3: New patch
---
 arch/csky/include/asm/uaccess.h | 1 -
 1 file changed, 1 deletion(-)

diff --git a/arch/csky/include/asm/uaccess.h b/arch/csky/include/asm/uaccess.h
index eaa1c3403a424..abefa125b93cf 100644
--- a/arch/csky/include/asm/uaccess.h
+++ b/arch/csky/include/asm/uaccess.h
@@ -11,7 +11,6 @@
 #include <linux/errno.h>
 #include <linux/types.h>
 #include <linux/sched.h>
-#include <linux/mm.h>
 #include <linux/string.h>
 #include <linux/version.h>
 #include <asm/segment.h>
-- 
2.26.0.rc2



^ permalink raw reply	[flat|nested] 38+ messages in thread

* [patch V3 08/20] hexagon: Remove mm.h from asm/uaccess.h
  2020-03-21 11:25 [patch V3 00/20] Lock ordering documentation and annotation for lockdep Thomas Gleixner
                   ` (6 preceding siblings ...)
  2020-03-21 11:25 ` [patch V3 07/20] csky: " Thomas Gleixner
@ 2020-03-21 11:25 ` " Thomas Gleixner
  2020-03-23 21:46   ` Brian Cain
  2020-03-21 11:25 ` [patch V3 09/20] ia64: " Thomas Gleixner
                   ` (12 subsequent siblings)
  20 siblings, 1 reply; 38+ messages in thread
From: Thomas Gleixner @ 2020-03-21 11:25 UTC (permalink / raw)
  To: LKML
  Cc: Peter Zijlstra, Ingo Molnar, Sebastian Siewior, Linus Torvalds,
	Joel Fernandes, Oleg Nesterov, Davidlohr Bueso,
	kbuild test robot, Brian Cain, linux-hexagon, Logan Gunthorpe,
	Bjorn Helgaas, Kurt Schwemmer, linux-pci, Greg Kroah-Hartman,
	Felipe Balbi, linux-usb, Kalle Valo, David S. Miller,
	linux-wireless, netdev, Darren Hart, Andy Shevchenko,
	platform-driver-x86, Zhang Rui, Rafael J. Wysocki, linux-pm,
	Len Brown, linux-acpi, Nick Hu, Greentime Hu, Vincent Chen,
	Guo Ren, linux-csky, Tony Luck, Fenghua Yu, linux-ia64,
	Michal Simek, Michael Ellerman, Arnd Bergmann, Geoff Levand,
	linuxppc-dev, Paul E . McKenney, Jonathan Corbet, Randy Dunlap,
	Davidlohr Bueso

From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

The defconfig compiles without linux/mm.h. With mm.h included the
include chain leands to:
|   CC      kernel/locking/percpu-rwsem.o
| In file included from include/linux/huge_mm.h:8,
|                  from include/linux/mm.h:567,
|                  from arch/hexagon/include/asm/uaccess.h:,
|                  from include/linux/uaccess.h:11,
|                  from include/linux/sched/task.h:11,
|                  from include/linux/sched/signal.h:9,
|                  from include/linux/rcuwait.h:6,
|                  from include/linux/percpu-rwsem.h:8,
|                  from kernel/locking/percpu-rwsem.c:6:
| include/linux/fs.h:1422:29: error: array type has incomplete element type 'struct percpu_rw_semaphore'
|  1422 |  struct percpu_rw_semaphore rw_sem[SB_FREEZE_LEVELS];

once rcuwait.h includes linux/sched/signal.h.

Remove the linux/mm.h include.

Reported-by: kbuild test robot <lkp@intel.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Brian Cain <bcain@codeaurora.org>
Cc: linux-hexagon@vger.kernel.org
---
V3: New patch
---
 arch/hexagon/include/asm/uaccess.h | 1 -
 1 file changed, 1 deletion(-)

diff --git a/arch/hexagon/include/asm/uaccess.h b/arch/hexagon/include/asm/uaccess.h
index 00cb38faad0c4..c1019a736ff13 100644
--- a/arch/hexagon/include/asm/uaccess.h
+++ b/arch/hexagon/include/asm/uaccess.h
@@ -10,7 +10,6 @@
 /*
  * User space memory access functions
  */
-#include <linux/mm.h>
 #include <asm/sections.h>
 
 /*
-- 
2.26.0.rc2



^ permalink raw reply	[flat|nested] 38+ messages in thread

* [patch V3 09/20] ia64: Remove mm.h from asm/uaccess.h
  2020-03-21 11:25 [patch V3 00/20] Lock ordering documentation and annotation for lockdep Thomas Gleixner
                   ` (7 preceding siblings ...)
  2020-03-21 11:25 ` [patch V3 08/20] hexagon: " Thomas Gleixner
@ 2020-03-21 11:25 ` " Thomas Gleixner
  2020-03-21 11:25 ` [patch V3 10/20] microblaze: " Thomas Gleixner
                   ` (11 subsequent siblings)
  20 siblings, 0 replies; 38+ messages in thread
From: Thomas Gleixner @ 2020-03-21 11:25 UTC (permalink / raw)
  To: LKML
  Cc: Peter Zijlstra, Ingo Molnar, Sebastian Siewior, Linus Torvalds,
	Joel Fernandes, Oleg Nesterov, Davidlohr Bueso,
	kbuild test robot, Tony Luck, Fenghua Yu, linux-ia64,
	Logan Gunthorpe, Bjorn Helgaas, Kurt Schwemmer, linux-pci,
	Greg Kroah-Hartman, Felipe Balbi, linux-usb, Kalle Valo,
	David S. Miller, linux-wireless, netdev, Darren Hart,
	Andy Shevchenko, platform-driver-x86, Zhang Rui,
	Rafael J. Wysocki, linux-pm, Len Brown, linux-acpi, Nick Hu,
	Greentime Hu, Vincent Chen, Guo Ren, linux-csky, Brian Cain,
	linux-hexagon, Michal Simek, Michael Ellerman, Arnd Bergmann,
	Geoff Levand, linuxppc-dev, Paul E . McKenney, Jonathan Corbet,
	Randy Dunlap, Davidlohr Bueso

From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

The defconfig compiles without linux/mm.h. With mm.h included the
include chain leands to:
|   CC      kernel/locking/percpu-rwsem.o
| In file included from include/linux/huge_mm.h:8,
|                  from include/linux/mm.h:567,
|                  from arch/ia64/include/asm/uaccess.h:,
|                  from include/linux/uaccess.h:11,
|                  from include/linux/sched/task.h:11,
|                  from include/linux/sched/signal.h:9,
|                  from include/linux/rcuwait.h:6,
|                  from include/linux/percpu-rwsem.h:8,
|                  from kernel/locking/percpu-rwsem.c:6:
| include/linux/fs.h:1422:29: error: array type has incomplete element type 'struct percpu_rw_semaphore'
|  1422 |  struct percpu_rw_semaphore rw_sem[SB_FREEZE_LEVELS];

once rcuwait.h includes linux/sched/signal.h.

Remove the linux/mm.h include.

Reported-by: kbuild test robot <lkp@intel.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: linux-ia64@vger.kernel.org
---
V3: New patch
---
 arch/ia64/include/asm/uaccess.h | 1 -
 arch/ia64/kernel/process.c      | 1 +
 arch/ia64/mm/ioremap.c          | 1 +
 3 files changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/ia64/include/asm/uaccess.h b/arch/ia64/include/asm/uaccess.h
index 89782ad3fb887..5c7e79eccaeed 100644
--- a/arch/ia64/include/asm/uaccess.h
+++ b/arch/ia64/include/asm/uaccess.h
@@ -35,7 +35,6 @@
 
 #include <linux/compiler.h>
 #include <linux/page-flags.h>
-#include <linux/mm.h>
 
 #include <asm/intrinsics.h>
 #include <asm/pgtable.h>
diff --git a/arch/ia64/kernel/process.c b/arch/ia64/kernel/process.c
index 968b5f33e725e..743aaf5283278 100644
--- a/arch/ia64/kernel/process.c
+++ b/arch/ia64/kernel/process.c
@@ -681,3 +681,4 @@ machine_power_off (void)
 	machine_halt();
 }
 
+EXPORT_SYMBOL(ia64_delay_loop);
diff --git a/arch/ia64/mm/ioremap.c b/arch/ia64/mm/ioremap.c
index a09cfa0645369..55fd3eb753ff9 100644
--- a/arch/ia64/mm/ioremap.c
+++ b/arch/ia64/mm/ioremap.c
@@ -8,6 +8,7 @@
 #include <linux/module.h>
 #include <linux/efi.h>
 #include <linux/io.h>
+#include <linux/mm.h>
 #include <linux/vmalloc.h>
 #include <asm/io.h>
 #include <asm/meminit.h>
-- 
2.26.0.rc2



^ permalink raw reply	[flat|nested] 38+ messages in thread

* [patch V3 10/20] microblaze: Remove mm.h from asm/uaccess.h
  2020-03-21 11:25 [patch V3 00/20] Lock ordering documentation and annotation for lockdep Thomas Gleixner
                   ` (8 preceding siblings ...)
  2020-03-21 11:25 ` [patch V3 09/20] ia64: " Thomas Gleixner
@ 2020-03-21 11:25 ` " Thomas Gleixner
  2020-03-21 11:25 ` [patch V3 11/20] rcuwait: Add @state argument to rcuwait_wait_event() Thomas Gleixner
                   ` (10 subsequent siblings)
  20 siblings, 0 replies; 38+ messages in thread
From: Thomas Gleixner @ 2020-03-21 11:25 UTC (permalink / raw)
  To: LKML
  Cc: Peter Zijlstra, Ingo Molnar, Sebastian Siewior, Linus Torvalds,
	Joel Fernandes, Oleg Nesterov, Davidlohr Bueso,
	kbuild test robot, Michal Simek, Logan Gunthorpe, Bjorn Helgaas,
	Kurt Schwemmer, linux-pci, Greg Kroah-Hartman, Felipe Balbi,
	linux-usb, Kalle Valo, David S. Miller, linux-wireless, netdev,
	Darren Hart, Andy Shevchenko, platform-driver-x86, Zhang Rui,
	Rafael J. Wysocki, linux-pm, Len Brown, linux-acpi, Nick Hu,
	Greentime Hu, Vincent Chen, Guo Ren, linux-csky, Brian Cain,
	linux-hexagon, Tony Luck, Fenghua Yu, linux-ia64,
	Michael Ellerman, Arnd Bergmann, Geoff Levand, linuxppc-dev,
	Paul E . McKenney, Jonathan Corbet, Randy Dunlap,
	Davidlohr Bueso

From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

The defconfig compiles without linux/mm.h. With mm.h included the
include chain leands to:
|   CC      kernel/locking/percpu-rwsem.o
| In file included from include/linux/huge_mm.h:8,
|                  from include/linux/mm.h:567,
|                  from arch/microblaze/include/asm/uaccess.h:,
|                  from include/linux/uaccess.h:11,
|                  from include/linux/sched/task.h:11,
|                  from include/linux/sched/signal.h:9,
|                  from include/linux/rcuwait.h:6,
|                  from include/linux/percpu-rwsem.h:8,
|                  from kernel/locking/percpu-rwsem.c:6:
| include/linux/fs.h:1422:29: error: array type has incomplete element type 'struct percpu_rw_semaphore'
|  1422 |  struct percpu_rw_semaphore rw_sem[SB_FREEZE_LEVELS];

once rcuwait.h includes linux/sched/signal.h.

Remove the linux/mm.h include.

Reported-by: kbuild test robot <lkp@intel.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Michal Simek <monstr@monstr.eu>
---
V3; New patch
---
 arch/microblaze/include/asm/uaccess.h | 1 -
 1 file changed, 1 deletion(-)

diff --git a/arch/microblaze/include/asm/uaccess.h b/arch/microblaze/include/asm/uaccess.h
index a1f206b90753a..4916d5fbea5e3 100644
--- a/arch/microblaze/include/asm/uaccess.h
+++ b/arch/microblaze/include/asm/uaccess.h
@@ -12,7 +12,6 @@
 #define _ASM_MICROBLAZE_UACCESS_H
 
 #include <linux/kernel.h>
-#include <linux/mm.h>
 
 #include <asm/mmu.h>
 #include <asm/page.h>
-- 
2.26.0.rc2



^ permalink raw reply	[flat|nested] 38+ messages in thread

* [patch V3 11/20] rcuwait: Add @state argument to rcuwait_wait_event()
  2020-03-21 11:25 [patch V3 00/20] Lock ordering documentation and annotation for lockdep Thomas Gleixner
                   ` (9 preceding siblings ...)
  2020-03-21 11:25 ` [patch V3 10/20] microblaze: " Thomas Gleixner
@ 2020-03-21 11:25 ` Thomas Gleixner
  2020-03-21 11:25 ` [patch V3 12/20] powerpc/ps3: Convert half completion to rcuwait Thomas Gleixner
                   ` (9 subsequent siblings)
  20 siblings, 0 replies; 38+ messages in thread
From: Thomas Gleixner @ 2020-03-21 11:25 UTC (permalink / raw)
  To: LKML
  Cc: Peter Zijlstra, Ingo Molnar, Sebastian Siewior, Linus Torvalds,
	Joel Fernandes, Oleg Nesterov, Davidlohr Bueso, Logan Gunthorpe,
	Bjorn Helgaas, Kurt Schwemmer, linux-pci, Greg Kroah-Hartman,
	Felipe Balbi, linux-usb, Kalle Valo, David S. Miller,
	linux-wireless, netdev, Darren Hart, Andy Shevchenko,
	platform-driver-x86, Zhang Rui, Rafael J. Wysocki, linux-pm,
	Len Brown, linux-acpi, kbuild test robot, Nick Hu, Greentime Hu,
	Vincent Chen, Guo Ren, linux-csky, Brian Cain, linux-hexagon,
	Tony Luck, Fenghua Yu, linux-ia64, Michal Simek,
	Michael Ellerman, Arnd Bergmann, Geoff Levand, linuxppc-dev,
	Paul E . McKenney, Jonathan Corbet, Randy Dunlap,
	Davidlohr Bueso

From: Peter Zijlstra (Intel) <peterz@infradead.org>

Extend rcuwait_wait_event() with a state variable so that it is not
restricted to UNINTERRUPTIBLE waits.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Davidlohr Bueso <dave@stgolabs.net>

---
 include/linux/rcuwait.h       |   12 ++++++++++--
 kernel/locking/percpu-rwsem.c |    2 +-
 2 files changed, 11 insertions(+), 3 deletions(-)

--- a/include/linux/rcuwait.h
+++ b/include/linux/rcuwait.h
@@ -3,6 +3,7 @@
 #define _LINUX_RCUWAIT_H_
 
 #include <linux/rcupdate.h>
+#include <linux/sched/signal.h>
 
 /*
  * rcuwait provides a way of blocking and waking up a single
@@ -30,23 +31,30 @@ extern void rcuwait_wake_up(struct rcuwa
  * The caller is responsible for locking around rcuwait_wait_event(),
  * such that writes to @task are properly serialized.
  */
-#define rcuwait_wait_event(w, condition)				\
+#define rcuwait_wait_event(w, condition, state)				\
 ({									\
+	int __ret = 0;							\
 	rcu_assign_pointer((w)->task, current);				\
 	for (;;) {							\
 		/*							\
 		 * Implicit barrier (A) pairs with (B) in		\
 		 * rcuwait_wake_up().					\
 		 */							\
-		set_current_state(TASK_UNINTERRUPTIBLE);		\
+		set_current_state(state);				\
 		if (condition)						\
 			break;						\
 									\
+		if (signal_pending_state(state, current)) {		\
+			__ret = -EINTR;					\
+			break;						\
+		}							\
+									\
 		schedule();						\
 	}								\
 									\
 	WRITE_ONCE((w)->task, NULL);					\
 	__set_current_state(TASK_RUNNING);				\
+	__ret;								\
 })
 
 #endif /* _LINUX_RCUWAIT_H_ */
--- a/kernel/locking/percpu-rwsem.c
+++ b/kernel/locking/percpu-rwsem.c
@@ -162,7 +162,7 @@ void percpu_down_write(struct percpu_rw_
 	 */
 
 	/* Wait for all now active readers to complete. */
-	rcuwait_wait_event(&sem->writer, readers_active_check(sem));
+	rcuwait_wait_event(&sem->writer, readers_active_check(sem), TASK_UNINTERRUPTIBLE);
 }
 EXPORT_SYMBOL_GPL(percpu_down_write);
 



^ permalink raw reply	[flat|nested] 38+ messages in thread

* [patch V3 12/20] powerpc/ps3: Convert half completion to rcuwait
  2020-03-21 11:25 [patch V3 00/20] Lock ordering documentation and annotation for lockdep Thomas Gleixner
                   ` (10 preceding siblings ...)
  2020-03-21 11:25 ` [patch V3 11/20] rcuwait: Add @state argument to rcuwait_wait_event() Thomas Gleixner
@ 2020-03-21 11:25 ` Thomas Gleixner
  2020-03-21 13:22   ` Thomas Gleixner
  2020-03-27 19:14   ` Geoff Levand
  2020-03-21 11:25 ` [patch V3 13/20] Documentation: Add lock ordering and nesting documentation Thomas Gleixner
                   ` (8 subsequent siblings)
  20 siblings, 2 replies; 38+ messages in thread
From: Thomas Gleixner @ 2020-03-21 11:25 UTC (permalink / raw)
  To: LKML
  Cc: Peter Zijlstra, Ingo Molnar, Sebastian Siewior, Linus Torvalds,
	Joel Fernandes, Oleg Nesterov, Davidlohr Bueso, Michael Ellerman,
	Arnd Bergmann, Geoff Levand, linuxppc-dev, Logan Gunthorpe,
	Bjorn Helgaas, Kurt Schwemmer, linux-pci, Greg Kroah-Hartman,
	Felipe Balbi, linux-usb, Kalle Valo, David S. Miller,
	linux-wireless, netdev, Darren Hart, Andy Shevchenko,
	platform-driver-x86, Zhang Rui, Rafael J. Wysocki, linux-pm,
	Len Brown, linux-acpi, kbuild test robot, Nick Hu, Greentime Hu,
	Vincent Chen, Guo Ren, linux-csky, Brian Cain, linux-hexagon,
	Tony Luck, Fenghua Yu, linux-ia64, Michal Simek,
	Paul E . McKenney, Jonathan Corbet, Randy Dunlap,
	Davidlohr Bueso

From: Thomas Gleixner <tglx@linutronix.de>

The PS3 notification interrupt and kthread use a hacked up completion to
communicate. Since we're wanting to change the completion implementation and
this is abuse anyway, replace it with a simple rcuwait since there is only ever
the one waiter.

AFAICT the kthread uses TASK_INTERRUPTIBLE to not increase loadavg, kthreads
cannot receive signals by default and this one doesn't look different. Use
TASK_IDLE instead.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Geoff Levand <geoff@infradead.org>
Cc: linuxppc-dev@lists.ozlabs.org
---
V3: Folded the init fix from bigeasy
V2: New patch to avoid the magic completion wait variant
---
 arch/powerpc/platforms/ps3/device-init.c |   18 +++++++++---------
 1 file changed, 9 insertions(+), 9 deletions(-)

--- a/arch/powerpc/platforms/ps3/device-init.c
+++ b/arch/powerpc/platforms/ps3/device-init.c
@@ -13,6 +13,7 @@
 #include <linux/init.h>
 #include <linux/slab.h>
 #include <linux/reboot.h>
+#include <linux/rcuwait.h>
 
 #include <asm/firmware.h>
 #include <asm/lv1call.h>
@@ -670,7 +671,8 @@ struct ps3_notification_device {
 	spinlock_t lock;
 	u64 tag;
 	u64 lv1_status;
-	struct completion done;
+	struct rcuwait wait;
+	bool done;
 };
 
 enum ps3_notify_type {
@@ -712,7 +714,8 @@ static irqreturn_t ps3_notification_inte
 		pr_debug("%s:%u: completed, status 0x%llx\n", __func__,
 			 __LINE__, status);
 		dev->lv1_status = status;
-		complete(&dev->done);
+		dev->done = true;
+		rcuwait_wake_up(&dev->wait);
 	}
 	spin_unlock(&dev->lock);
 	return IRQ_HANDLED;
@@ -725,12 +728,12 @@ static int ps3_notification_read_write(s
 	unsigned long flags;
 	int res;
 
-	init_completion(&dev->done);
 	spin_lock_irqsave(&dev->lock, flags);
 	res = write ? lv1_storage_write(dev->sbd.dev_id, 0, 0, 1, 0, lpar,
 					&dev->tag)
 		    : lv1_storage_read(dev->sbd.dev_id, 0, 0, 1, 0, lpar,
 				       &dev->tag);
+	dev->done = false;
 	spin_unlock_irqrestore(&dev->lock, flags);
 	if (res) {
 		pr_err("%s:%u: %s failed %d\n", __func__, __LINE__, op, res);
@@ -738,14 +741,10 @@ static int ps3_notification_read_write(s
 	}
 	pr_debug("%s:%u: notification %s issued\n", __func__, __LINE__, op);
 
-	res = wait_event_interruptible(dev->done.wait,
-				       dev->done.done || kthread_should_stop());
+	rcuwait_wait_event(&dev->wait, dev->done || kthread_should_stop(), TASK_IDLE);
+
 	if (kthread_should_stop())
 		res = -EINTR;
-	if (res) {
-		pr_debug("%s:%u: interrupted %s\n", __func__, __LINE__, op);
-		return res;
-	}
 
 	if (dev->lv1_status) {
 		pr_err("%s:%u: %s not completed, status 0x%llx\n", __func__,
@@ -810,6 +809,7 @@ static int ps3_probe_thread(void *data)
 	}
 
 	spin_lock_init(&dev.lock);
+	rcuwait_init(&dev.wait);
 
 	res = request_irq(irq, ps3_notification_interrupt, 0,
 			  "ps3_notification", &dev);


^ permalink raw reply	[flat|nested] 38+ messages in thread

* [patch V3 13/20] Documentation: Add lock ordering and nesting documentation
  2020-03-21 11:25 [patch V3 00/20] Lock ordering documentation and annotation for lockdep Thomas Gleixner
                   ` (11 preceding siblings ...)
  2020-03-21 11:25 ` [patch V3 12/20] powerpc/ps3: Convert half completion to rcuwait Thomas Gleixner
@ 2020-03-21 11:25 ` Thomas Gleixner
  2020-03-23  2:55   ` Paul E. McKenney
  2020-03-21 11:25 ` [patch V3 14/20] timekeeping: Split jiffies seqlock Thomas Gleixner
                   ` (7 subsequent siblings)
  20 siblings, 1 reply; 38+ messages in thread
From: Thomas Gleixner @ 2020-03-21 11:25 UTC (permalink / raw)
  To: LKML
  Cc: Peter Zijlstra, Ingo Molnar, Sebastian Siewior, Linus Torvalds,
	Joel Fernandes, Oleg Nesterov, Davidlohr Bueso,
	Paul E . McKenney, Jonathan Corbet, Randy Dunlap,
	Logan Gunthorpe, Bjorn Helgaas, Kurt Schwemmer, linux-pci,
	Greg Kroah-Hartman, Felipe Balbi, linux-usb, Kalle Valo,
	David S. Miller, linux-wireless, netdev, Darren Hart,
	Andy Shevchenko, platform-driver-x86, Zhang Rui,
	Rafael J. Wysocki, linux-pm, Len Brown, linux-acpi,
	kbuild test robot, Nick Hu, Greentime Hu, Vincent Chen, Guo Ren,
	linux-csky, Brian Cain, linux-hexagon, Tony Luck, Fenghua Yu,
	linux-ia64, Michal Simek, Michael Ellerman, Arnd Bergmann,
	Geoff Levand, linuxppc-dev, Davidlohr Bueso

From: Thomas Gleixner <tglx@linutronix.de>

The kernel provides a variety of locking primitives. The nesting of these
lock types and the implications of them on RT enabled kernels is nowhere
documented.

Add initial documentation.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: "Paul E . McKenney" <paulmck@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Randy Dunlap <rdunlap@infradead.org>
---
V3: Addressed review comments from Paul, Jonathan, Davidlohr
V2: Addressed review comments from Randy
---
 Documentation/locking/index.rst     |    1 
 Documentation/locking/locktypes.rst |  299 ++++++++++++++++++++++++++++++++++++
 2 files changed, 300 insertions(+)
 create mode 100644 Documentation/locking/locktypes.rst

--- a/Documentation/locking/index.rst
+++ b/Documentation/locking/index.rst
@@ -7,6 +7,7 @@ locking
 .. toctree::
     :maxdepth: 1
 
+    locktypes
     lockdep-design
     lockstat
     locktorture
--- /dev/null
+++ b/Documentation/locking/locktypes.rst
@@ -0,0 +1,299 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+.. _kernel_hacking_locktypes:
+
+==========================
+Lock types and their rules
+==========================
+
+Introduction
+============
+
+The kernel provides a variety of locking primitives which can be divided
+into two categories:
+
+ - Sleeping locks
+ - Spinning locks
+
+This document conceptually describes these lock types and provides rules
+for their nesting, including the rules for use under PREEMPT_RT.
+
+
+Lock categories
+===============
+
+Sleeping locks
+--------------
+
+Sleeping locks can only be acquired in preemptible task context.
+
+Although implementations allow try_lock() from other contexts, it is
+necessary to carefully evaluate the safety of unlock() as well as of
+try_lock().  Furthermore, it is also necessary to evaluate the debugging
+versions of these primitives.  In short, don't acquire sleeping locks from
+other contexts unless there is no other option.
+
+Sleeping lock types:
+
+ - mutex
+ - rt_mutex
+ - semaphore
+ - rw_semaphore
+ - ww_mutex
+ - percpu_rw_semaphore
+
+On PREEMPT_RT kernels, these lock types are converted to sleeping locks:
+
+ - spinlock_t
+ - rwlock_t
+
+Spinning locks
+--------------
+
+ - raw_spinlock_t
+ - bit spinlocks
+
+On non-PREEMPT_RT kernels, these lock types are also spinning locks:
+
+ - spinlock_t
+ - rwlock_t
+
+Spinning locks implicitly disable preemption and the lock / unlock functions
+can have suffixes which apply further protections:
+
+ ===================  ====================================================
+ _bh()                Disable / enable bottom halves (soft interrupts)
+ _irq()               Disable / enable interrupts
+ _irqsave/restore()   Save and disable / restore interrupt disabled state
+ ===================  ====================================================
+
+
+rtmutex
+=======
+
+RT-mutexes are mutexes with support for priority inheritance (PI).
+
+PI has limitations on non PREEMPT_RT enabled kernels due to preemption and
+interrupt disabled sections.
+
+PI clearly cannot preempt preemption-disabled or interrupt-disabled
+regions of code, even on PREEMPT_RT kernels.  Instead, PREEMPT_RT kernels
+execute most such regions of code in preemptible task context, especially
+interrupt handlers and soft interrupts.  This conversion allows spinlock_t
+and rwlock_t to be implemented via RT-mutexes.
+
+
+raw_spinlock_t and spinlock_t
+=============================
+
+raw_spinlock_t
+--------------
+
+raw_spinlock_t is a strict spinning lock implementation regardless of the
+kernel configuration including PREEMPT_RT enabled kernels.
+
+raw_spinlock_t is a strict spinning lock implementation in all kernels,
+including PREEMPT_RT kernels.  Use raw_spinlock_t only in real critical
+core code, low level interrupt handling and places where disabling
+preemption or interrupts is required, for example, to safely access
+hardware state.  raw_spinlock_t can sometimes also be used when the
+critical section is tiny, thus avoiding RT-mutex overhead.
+
+spinlock_t
+----------
+
+The semantics of spinlock_t change with the state of CONFIG_PREEMPT_RT.
+
+On a non PREEMPT_RT enabled kernel spinlock_t is mapped to raw_spinlock_t
+and has exactly the same semantics.
+
+spinlock_t and PREEMPT_RT
+-------------------------
+
+On a PREEMPT_RT enabled kernel spinlock_t is mapped to a separate
+implementation based on rt_mutex which changes the semantics:
+
+ - Preemption is not disabled
+
+ - The hard interrupt related suffixes for spin_lock / spin_unlock
+   operations (_irq, _irqsave / _irqrestore) do not affect the CPUs
+   interrupt disabled state
+
+ - The soft interrupt related suffix (_bh()) still disables softirq
+   handlers.
+
+   Non-PREEMPT_RT kernels disable preemption to get this effect.
+
+   PREEMPT_RT kernels use a per-CPU lock for serialization which keeps
+   preemption disabled. The lock disables softirq handlers and also
+   prevents reentrancy due to task preemption.
+
+PREEMPT_RT kernels preserve all other spinlock_t semantics:
+
+ - Tasks holding a spinlock_t do not migrate.  Non-PREEMPT_RT kernels
+   avoid migration by disabling preemption.  PREEMPT_RT kernels instead
+   disable migration, which ensures that pointers to per-CPU variables
+   remain valid even if the task is preempted.
+
+ - Task state is preserved across spinlock acquisition, ensuring that the
+   task-state rules apply to all kernel configurations.  Non-PREEMPT_RT
+   kernels leave task state untouched.  However, PREEMPT_RT must change
+   task state if the task blocks during acquisition.  Therefore, it saves
+   the current task state before blocking and the corresponding lock wakeup
+   restores it.
+
+   Other types of wakeups would normally unconditionally set the task state
+   to RUNNING, but that does not work here because the task must remain
+   blocked until the lock becomes available.  Therefore, when a non-lock
+   wakeup attempts to awaken a task blocked waiting for a spinlock, it
+   instead sets the saved state to RUNNING.  Then, when the lock
+   acquisition completes, the lock wakeup sets the task state to the saved
+   state, in this case setting it to RUNNING.
+
+rwlock_t
+========
+
+rwlock_t is a multiple readers and single writer lock mechanism.
+
+Non-PREEMPT_RT kernels implement rwlock_t as a spinning lock and the
+suffix rules of spinlock_t apply accordingly. The implementation is fair,
+thus preventing writer starvation.
+
+rwlock_t and PREEMPT_RT
+-----------------------
+
+PREEMPT_RT kernels map rwlock_t to a separate rt_mutex-based
+implementation, thus changing semantics:
+
+ - All the spinlock_t changes also apply to rwlock_t.
+
+ - Because an rwlock_t writer cannot grant its priority to multiple
+   readers, a preempted low-priority reader will continue holding its lock,
+   thus starving even high-priority writers.  In contrast, because readers
+   can grant their priority to a writer, a preempted low-priority writer
+   will have its priority boosted until it releases the lock, thus
+   preventing that writer from starving readers.
+
+
+PREEMPT_RT caveats
+==================
+
+spinlock_t and rwlock_t
+-----------------------
+
+These changes in spinlock_t and rwlock_t semantics on PREEMPT_RT kernels
+have a few implications.  For example, on a non-PREEMPT_RT kernel the
+following code sequence works as expected::
+
+   local_irq_disable();
+   spin_lock(&lock);
+
+and is fully equivalent to::
+
+   spin_lock_irq(&lock);
+
+Same applies to rwlock_t and the _irqsave() suffix variants.
+
+On PREEMPT_RT kernel this code sequence breaks because RT-mutex requires a
+fully preemptible context.  Instead, use spin_lock_irq() or
+spin_lock_irqsave() and their unlock counterparts.  In cases where the
+interrupt disabling and locking must remain separate, PREEMPT_RT offers a
+local_lock mechanism.  Acquiring the local_lock pins the task to a CPU,
+allowing things like per-CPU irq-disabled locks to be acquired.  However,
+this approach should be used only where absolutely necessary.
+
+
+raw_spinlock_t
+--------------
+
+Acquiring a raw_spinlock_t disables preemption and possibly also
+interrupts, so the critical section must avoid acquiring a regular
+spinlock_t or rwlock_t, for example, the critical section must avoid
+allocating memory.  Thus, on a non-PREEMPT_RT kernel the following code
+works perfectly::
+
+  raw_spin_lock(&lock);
+  p = kmalloc(sizeof(*p), GFP_ATOMIC);
+
+But this code fails on PREEMPT_RT kernels because the memory allocator is
+fully preemptible and therefore cannot be invoked from truly atomic
+contexts.  However, it is perfectly fine to invoke the memory allocator
+while holding normal non-raw spinlocks because they do not disable
+preemption on PREEMPT_RT kernels::
+
+  spin_lock(&lock);
+  p = kmalloc(sizeof(*p), GFP_ATOMIC);
+
+
+bit spinlocks
+-------------
+
+Bit spinlocks are problematic for PREEMPT_RT as they cannot be easily
+substituted by an RT-mutex based implementation for obvious reasons.
+
+The semantics of bit spinlocks are preserved on PREEMPT_RT kernels and the
+caveats vs. raw_spinlock_t apply.
+
+Some bit spinlocks are substituted by regular spinlock_t for PREEMPT_RT but
+this requires conditional (#ifdef'ed) code changes at the usage site while
+the spinlock_t substitution is simply done by the compiler and the
+conditionals are restricted to header files and core implementation of the
+locking primitives and the usage sites do not require any changes.
+
+
+Lock type nesting rules
+=======================
+
+The most basic rules are:
+
+  - Lock types of the same lock category (sleeping, spinning) can nest
+    arbitrarily as long as they respect the general lock ordering rules to
+    prevent deadlocks.
+
+  - Sleeping lock types cannot nest inside spinning lock types.
+
+  - Spinning lock types can nest inside sleeping lock types.
+
+These rules apply in general independent of CONFIG_PREEMPT_RT.
+
+As PREEMPT_RT changes the lock category of spinlock_t and rwlock_t from
+spinning to sleeping this has obviously restrictions how they can nest with
+raw_spinlock_t.
+
+This results in the following nest ordering:
+
+  1) Sleeping locks
+  2) spinlock_t and rwlock_t
+  3) raw_spinlock_t and bit spinlocks
+
+Lockdep is aware of these constraints to ensure that they are respected.
+
+
+Owner semantics
+===============
+
+Most lock types in the Linux kernel have strict owner semantics, i.e. the
+context (task) which acquires a lock has to release it.
+
+There are two exceptions:
+
+  - semaphores
+  - rwsems
+
+semaphores have no owner semantics for historical reason, and as such
+trylock and release operations can be called from any context. They are
+often used for both serialization and waiting purposes. That's generally
+discouraged and should be replaced by separate serialization and wait
+mechanisms, such as mutexes and completions.
+
+rwsems have grown interfaces which allow non owner release for special
+purposes. This usage is problematic on PREEMPT_RT because PREEMPT_RT
+substitutes all locking primitives except semaphores with RT-mutex based
+implementations to provide priority inheritance for all lock types except
+the truly spinning ones. Priority inheritance on ownerless locks is
+obviously impossible.
+
+For now the rwsem non-owner release excludes code which utilizes it from
+being used on PREEMPT_RT enabled kernels. In same cases this can be
+mitigated by disabling portions of the code, in other cases the complete
+functionality has to be disabled until a workable solution has been found.


^ permalink raw reply	[flat|nested] 38+ messages in thread

* [patch V3 14/20] timekeeping: Split jiffies seqlock
  2020-03-21 11:25 [patch V3 00/20] Lock ordering documentation and annotation for lockdep Thomas Gleixner
                   ` (12 preceding siblings ...)
  2020-03-21 11:25 ` [patch V3 13/20] Documentation: Add lock ordering and nesting documentation Thomas Gleixner
@ 2020-03-21 11:25 ` Thomas Gleixner
  2020-03-21 11:25 ` [patch V3 15/20] sched/swait: Prepare usage in completions Thomas Gleixner
                   ` (6 subsequent siblings)
  20 siblings, 0 replies; 38+ messages in thread
From: Thomas Gleixner @ 2020-03-21 11:25 UTC (permalink / raw)
  To: LKML
  Cc: Peter Zijlstra, Ingo Molnar, Sebastian Siewior, Linus Torvalds,
	Joel Fernandes, Oleg Nesterov, Davidlohr Bueso, Logan Gunthorpe,
	Bjorn Helgaas, Kurt Schwemmer, linux-pci, Greg Kroah-Hartman,
	Felipe Balbi, linux-usb, Kalle Valo, David S. Miller,
	linux-wireless, netdev, Darren Hart, Andy Shevchenko,
	platform-driver-x86, Zhang Rui, Rafael J. Wysocki, linux-pm,
	Len Brown, linux-acpi, kbuild test robot, Nick Hu, Greentime Hu,
	Vincent Chen, Guo Ren, linux-csky, Brian Cain, linux-hexagon,
	Tony Luck, Fenghua Yu, linux-ia64, Michal Simek,
	Michael Ellerman, Arnd Bergmann, Geoff Levand, linuxppc-dev,
	Paul E . McKenney, Jonathan Corbet, Randy Dunlap,
	Davidlohr Bueso

From: Thomas Gleixner <tglx@linutronix.de>

seqlock consists of a sequence counter and a spinlock_t which is used to
serialize the writers. spinlock_t is substituted by a "sleeping" spinlock
on PREEMPT_RT enabled kernels which breaks the usage in the timekeeping
code as the writers are executed in hard interrupt and therefore
non-preemptible context even on PREEMPT_RT.

The spinlock in seqlock cannot be unconditionally replaced by a
raw_spinlock_t as many seqlock users have nesting spinlock sections or
other code which is not suitable to run in truly atomic context on RT.

Instead of providing a raw_seqlock API for a single use case, open code the
seqlock for the jiffies use case and implement it with a raw_spinlock_t and
a sequence counter.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

---
 kernel/time/jiffies.c     |    7 ++++---
 kernel/time/tick-common.c |   10 ++++++----
 kernel/time/tick-sched.c  |   19 ++++++++++++-------
 kernel/time/timekeeping.c |    6 ++++--
 kernel/time/timekeeping.h |    3 ++-
 5 files changed, 28 insertions(+), 17 deletions(-)

--- a/kernel/time/jiffies.c
+++ b/kernel/time/jiffies.c
@@ -58,7 +58,8 @@ static struct clocksource clocksource_ji
 	.max_cycles	= 10,
 };
 
-__cacheline_aligned_in_smp DEFINE_SEQLOCK(jiffies_lock);
+__cacheline_aligned_in_smp DEFINE_RAW_SPINLOCK(jiffies_lock);
+__cacheline_aligned_in_smp seqcount_t jiffies_seq;
 
 #if (BITS_PER_LONG < 64)
 u64 get_jiffies_64(void)
@@ -67,9 +68,9 @@ u64 get_jiffies_64(void)
 	u64 ret;
 
 	do {
-		seq = read_seqbegin(&jiffies_lock);
+		seq = read_seqcount_begin(&jiffies_seq);
 		ret = jiffies_64;
-	} while (read_seqretry(&jiffies_lock, seq));
+	} while (read_seqcount_retry(&jiffies_seq, seq));
 	return ret;
 }
 EXPORT_SYMBOL(get_jiffies_64);
--- a/kernel/time/tick-common.c
+++ b/kernel/time/tick-common.c
@@ -84,13 +84,15 @@ int tick_is_oneshot_available(void)
 static void tick_periodic(int cpu)
 {
 	if (tick_do_timer_cpu == cpu) {
-		write_seqlock(&jiffies_lock);
+		raw_spin_lock(&jiffies_lock);
+		write_seqcount_begin(&jiffies_seq);
 
 		/* Keep track of the next tick event */
 		tick_next_period = ktime_add(tick_next_period, tick_period);
 
 		do_timer(1);
-		write_sequnlock(&jiffies_lock);
+		write_seqcount_end(&jiffies_seq);
+		raw_spin_unlock(&jiffies_lock);
 		update_wall_time();
 	}
 
@@ -162,9 +164,9 @@ void tick_setup_periodic(struct clock_ev
 		ktime_t next;
 
 		do {
-			seq = read_seqbegin(&jiffies_lock);
+			seq = read_seqcount_begin(&jiffies_seq);
 			next = tick_next_period;
-		} while (read_seqretry(&jiffies_lock, seq));
+		} while (read_seqcount_retry(&jiffies_seq, seq));
 
 		clockevents_switch_state(dev, CLOCK_EVT_STATE_ONESHOT);
 
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -65,7 +65,8 @@ static void tick_do_update_jiffies64(kti
 		return;
 
 	/* Reevaluate with jiffies_lock held */
-	write_seqlock(&jiffies_lock);
+	raw_spin_lock(&jiffies_lock);
+	write_seqcount_begin(&jiffies_seq);
 
 	delta = ktime_sub(now, last_jiffies_update);
 	if (delta >= tick_period) {
@@ -91,10 +92,12 @@ static void tick_do_update_jiffies64(kti
 		/* Keep the tick_next_period variable up to date */
 		tick_next_period = ktime_add(last_jiffies_update, tick_period);
 	} else {
-		write_sequnlock(&jiffies_lock);
+		write_seqcount_end(&jiffies_seq);
+		raw_spin_unlock(&jiffies_lock);
 		return;
 	}
-	write_sequnlock(&jiffies_lock);
+	write_seqcount_end(&jiffies_seq);
+	raw_spin_unlock(&jiffies_lock);
 	update_wall_time();
 }
 
@@ -105,12 +108,14 @@ static ktime_t tick_init_jiffy_update(vo
 {
 	ktime_t period;
 
-	write_seqlock(&jiffies_lock);
+	raw_spin_lock(&jiffies_lock);
+	write_seqcount_begin(&jiffies_seq);
 	/* Did we start the jiffies update yet ? */
 	if (last_jiffies_update == 0)
 		last_jiffies_update = tick_next_period;
 	period = last_jiffies_update;
-	write_sequnlock(&jiffies_lock);
+	write_seqcount_end(&jiffies_seq);
+	raw_spin_unlock(&jiffies_lock);
 	return period;
 }
 
@@ -676,10 +681,10 @@ static ktime_t tick_nohz_next_event(stru
 
 	/* Read jiffies and the time when jiffies were updated last */
 	do {
-		seq = read_seqbegin(&jiffies_lock);
+		seq = read_seqcount_begin(&jiffies_seq);
 		basemono = last_jiffies_update;
 		basejiff = jiffies;
-	} while (read_seqretry(&jiffies_lock, seq));
+	} while (read_seqcount_retry(&jiffies_seq, seq));
 	ts->last_jiffies = basejiff;
 	ts->timer_expires_base = basemono;
 
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -2397,8 +2397,10 @@ EXPORT_SYMBOL(hardpps);
  */
 void xtime_update(unsigned long ticks)
 {
-	write_seqlock(&jiffies_lock);
+	raw_spin_lock(&jiffies_lock);
+	write_seqcount_begin(&jiffies_seq);
 	do_timer(ticks);
-	write_sequnlock(&jiffies_lock);
+	write_seqcount_end(&jiffies_seq);
+	raw_spin_unlock(&jiffies_lock);
 	update_wall_time();
 }
--- a/kernel/time/timekeeping.h
+++ b/kernel/time/timekeeping.h
@@ -25,7 +25,8 @@ static inline void sched_clock_resume(vo
 extern void do_timer(unsigned long ticks);
 extern void update_wall_time(void);
 
-extern seqlock_t jiffies_lock;
+extern raw_spinlock_t jiffies_lock;
+extern seqcount_t jiffies_seq;
 
 #define CS_NAME_LEN	32
 



^ permalink raw reply	[flat|nested] 38+ messages in thread

* [patch V3 15/20] sched/swait: Prepare usage in completions
  2020-03-21 11:25 [patch V3 00/20] Lock ordering documentation and annotation for lockdep Thomas Gleixner
                   ` (13 preceding siblings ...)
  2020-03-21 11:25 ` [patch V3 14/20] timekeeping: Split jiffies seqlock Thomas Gleixner
@ 2020-03-21 11:25 ` Thomas Gleixner
  2020-03-21 11:26 ` [patch V3 16/20] completion: Use simple wait queues Thomas Gleixner
                   ` (5 subsequent siblings)
  20 siblings, 0 replies; 38+ messages in thread
From: Thomas Gleixner @ 2020-03-21 11:25 UTC (permalink / raw)
  To: LKML
  Cc: Peter Zijlstra, Ingo Molnar, Sebastian Siewior, Linus Torvalds,
	Joel Fernandes, Oleg Nesterov, Davidlohr Bueso, Logan Gunthorpe,
	Bjorn Helgaas, Kurt Schwemmer, linux-pci, Greg Kroah-Hartman,
	Felipe Balbi, linux-usb, Kalle Valo, David S. Miller,
	linux-wireless, netdev, Darren Hart, Andy Shevchenko,
	platform-driver-x86, Zhang Rui, Rafael J. Wysocki, linux-pm,
	Len Brown, linux-acpi, kbuild test robot, Nick Hu, Greentime Hu,
	Vincent Chen, Guo Ren, linux-csky, Brian Cain, linux-hexagon,
	Tony Luck, Fenghua Yu, linux-ia64, Michal Simek,
	Michael Ellerman, Arnd Bergmann, Geoff Levand, linuxppc-dev,
	Paul E . McKenney, Jonathan Corbet, Randy Dunlap,
	Davidlohr Bueso

From: Thomas Gleixner <tglx@linutronix.de>

As a preparation to use simple wait queues for completions:

  - Provide swake_up_all_locked() to support complete_all()
  - Make __prepare_to_swait() public available

This is done to enable the usage of complete() within truly atomic contexts
on a PREEMPT_RT enabled kernel.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
---
V2: Add comment to swake_up_all_locked()
---
 kernel/sched/sched.h |    3 +++
 kernel/sched/swait.c |   15 ++++++++++++++-
 2 files changed, 17 insertions(+), 1 deletion(-)

--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -2492,3 +2492,6 @@ static inline bool is_per_cpu_kthread(st
 	return true;
 }
 #endif
+
+void swake_up_all_locked(struct swait_queue_head *q);
+void __prepare_to_swait(struct swait_queue_head *q, struct swait_queue *wait);
--- a/kernel/sched/swait.c
+++ b/kernel/sched/swait.c
@@ -32,6 +32,19 @@ void swake_up_locked(struct swait_queue_
 }
 EXPORT_SYMBOL(swake_up_locked);
 
+/*
+ * Wake up all waiters. This is an interface which is solely exposed for
+ * completions and not for general usage.
+ *
+ * It is intentionally different from swake_up_all() to allow usage from
+ * hard interrupt context and interrupt disabled regions.
+ */
+void swake_up_all_locked(struct swait_queue_head *q)
+{
+	while (!list_empty(&q->task_list))
+		swake_up_locked(q);
+}
+
 void swake_up_one(struct swait_queue_head *q)
 {
 	unsigned long flags;
@@ -69,7 +82,7 @@ void swake_up_all(struct swait_queue_hea
 }
 EXPORT_SYMBOL(swake_up_all);
 
-static void __prepare_to_swait(struct swait_queue_head *q, struct swait_queue *wait)
+void __prepare_to_swait(struct swait_queue_head *q, struct swait_queue *wait)
 {
 	wait->task = current;
 	if (list_empty(&wait->task_list))



^ permalink raw reply	[flat|nested] 38+ messages in thread

* [patch V3 16/20] completion: Use simple wait queues
  2020-03-21 11:25 [patch V3 00/20] Lock ordering documentation and annotation for lockdep Thomas Gleixner
                   ` (14 preceding siblings ...)
  2020-03-21 11:25 ` [patch V3 15/20] sched/swait: Prepare usage in completions Thomas Gleixner
@ 2020-03-21 11:26 ` Thomas Gleixner
  2020-03-23 15:20   ` [PATCH] completion: Use lockdep_assert_RT_in_threaded_ctx() in complete_all() Sebastian Siewior
  2020-03-21 11:26 ` [patch V3 17/20] lockdep: Introduce wait-type checks Thomas Gleixner
                   ` (4 subsequent siblings)
  20 siblings, 1 reply; 38+ messages in thread
From: Thomas Gleixner @ 2020-03-21 11:26 UTC (permalink / raw)
  To: LKML
  Cc: Peter Zijlstra, Ingo Molnar, Sebastian Siewior, Linus Torvalds,
	Joel Fernandes, Oleg Nesterov, Davidlohr Bueso, Davidlohr Bueso,
	Greg Kroah-Hartman, Logan Gunthorpe, Bjorn Helgaas,
	Kurt Schwemmer, linux-pci, Felipe Balbi, linux-usb, Kalle Valo,
	David S. Miller, linux-wireless, netdev, Darren Hart,
	Andy Shevchenko, platform-driver-x86, Zhang Rui,
	Rafael J. Wysocki, linux-pm, Len Brown, linux-acpi,
	kbuild test robot, Nick Hu, Greentime Hu, Vincent Chen, Guo Ren,
	linux-csky, Brian Cain, linux-hexagon, Tony Luck, Fenghua Yu,
	linux-ia64, Michal Simek, Michael Ellerman, Arnd Bergmann,
	Geoff Levand, linuxppc-dev, Paul E . McKenney, Jonathan Corbet,
	Randy Dunlap

From: Thomas Gleixner <tglx@linutronix.de>

completion uses a wait_queue_head_t to enqueue waiters.

wait_queue_head_t contains a spinlock_t to protect the list of waiters
which excludes it from being used in truly atomic context on a PREEMPT_RT
enabled kernel.

The spinlock in the wait queue head cannot be replaced by a raw_spinlock
because:

  - wait queues can have custom wakeup callbacks, which acquire other
    spinlock_t locks and have potentially long execution times

  - wake_up() walks an unbounded number of list entries during the wake up
    and may wake an unbounded number of waiters.

For simplicity and performance reasons complete() should be usable on
PREEMPT_RT enabled kernels.

completions do not use custom wakeup callbacks and are usually single
waiter, except for a few corner cases.

Replace the wait queue in the completion with a simple wait queue (swait),
which uses a raw_spinlock_t for protecting the waiter list and therefore is
safe to use inside truly atomic regions on PREEMPT_RT.

There is no semantical or functional change:

  - completions use the exclusive wait mode which is what swait provides

  - complete() wakes one exclusive waiter

  - complete_all() wakes all waiters while holding the lock which protects
    the wait queue against newly incoming waiters. The conversion to swait
    preserves this behaviour.

complete_all() might cause unbound latencies with a large number of waiters
being woken at once, but most complete_all() usage sites are either in
testing or initialization code or have only a really small number of
concurrent waiters which for now does not cause a latency problem. Keep it
simple for now.

The fixup of the warning check in the USB gadget driver is just a straight
forward conversion of the lockless waiter check from one waitqueue type to
the other.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Reviewed-by: Davidlohr Bueso <dbueso@suse.de>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
---
V2: Split out the orinoco and usb gadget parts and amended change log
---
 drivers/usb/gadget/function/f_fs.c |    2 +-
 include/linux/completion.h         |    8 ++++----
 kernel/sched/completion.c          |   36 +++++++++++++++++++-----------------
 3 files changed, 24 insertions(+), 22 deletions(-)

--- a/drivers/usb/gadget/function/f_fs.c
+++ b/drivers/usb/gadget/function/f_fs.c
@@ -1703,7 +1703,7 @@ static void ffs_data_put(struct ffs_data
 		pr_info("%s(): freeing\n", __func__);
 		ffs_data_clear(ffs);
 		BUG_ON(waitqueue_active(&ffs->ev.waitq) ||
-		       waitqueue_active(&ffs->ep0req_completion.wait) ||
+		       swait_active(&ffs->ep0req_completion.wait) ||
 		       waitqueue_active(&ffs->wait));
 		destroy_workqueue(ffs->io_completion_wq);
 		kfree(ffs->dev_name);
--- a/include/linux/completion.h
+++ b/include/linux/completion.h
@@ -9,7 +9,7 @@
  * See kernel/sched/completion.c for details.
  */
 
-#include <linux/wait.h>
+#include <linux/swait.h>
 
 /*
  * struct completion - structure used to maintain state for a "completion"
@@ -25,7 +25,7 @@
  */
 struct completion {
 	unsigned int done;
-	wait_queue_head_t wait;
+	struct swait_queue_head wait;
 };
 
 #define init_completion_map(x, m) __init_completion(x)
@@ -34,7 +34,7 @@ static inline void complete_acquire(stru
 static inline void complete_release(struct completion *x) {}
 
 #define COMPLETION_INITIALIZER(work) \
-	{ 0, __WAIT_QUEUE_HEAD_INITIALIZER((work).wait) }
+	{ 0, __SWAIT_QUEUE_HEAD_INITIALIZER((work).wait) }
 
 #define COMPLETION_INITIALIZER_ONSTACK_MAP(work, map) \
 	(*({ init_completion_map(&(work), &(map)); &(work); }))
@@ -85,7 +85,7 @@ static inline void complete_release(stru
 static inline void __init_completion(struct completion *x)
 {
 	x->done = 0;
-	init_waitqueue_head(&x->wait);
+	init_swait_queue_head(&x->wait);
 }
 
 /**
--- a/kernel/sched/completion.c
+++ b/kernel/sched/completion.c
@@ -29,12 +29,12 @@ void complete(struct completion *x)
 {
 	unsigned long flags;
 
-	spin_lock_irqsave(&x->wait.lock, flags);
+	raw_spin_lock_irqsave(&x->wait.lock, flags);
 
 	if (x->done != UINT_MAX)
 		x->done++;
-	__wake_up_locked(&x->wait, TASK_NORMAL, 1);
-	spin_unlock_irqrestore(&x->wait.lock, flags);
+	swake_up_locked(&x->wait);
+	raw_spin_unlock_irqrestore(&x->wait.lock, flags);
 }
 EXPORT_SYMBOL(complete);
 
@@ -58,10 +58,12 @@ void complete_all(struct completion *x)
 {
 	unsigned long flags;
 
-	spin_lock_irqsave(&x->wait.lock, flags);
+	WARN_ON(irqs_disabled());
+
+	raw_spin_lock_irqsave(&x->wait.lock, flags);
 	x->done = UINT_MAX;
-	__wake_up_locked(&x->wait, TASK_NORMAL, 0);
-	spin_unlock_irqrestore(&x->wait.lock, flags);
+	swake_up_all_locked(&x->wait);
+	raw_spin_unlock_irqrestore(&x->wait.lock, flags);
 }
 EXPORT_SYMBOL(complete_all);
 
@@ -70,20 +72,20 @@ do_wait_for_common(struct completion *x,
 		   long (*action)(long), long timeout, int state)
 {
 	if (!x->done) {
-		DECLARE_WAITQUEUE(wait, current);
+		DECLARE_SWAITQUEUE(wait);
 
-		__add_wait_queue_entry_tail_exclusive(&x->wait, &wait);
 		do {
 			if (signal_pending_state(state, current)) {
 				timeout = -ERESTARTSYS;
 				break;
 			}
+			__prepare_to_swait(&x->wait, &wait);
 			__set_current_state(state);
-			spin_unlock_irq(&x->wait.lock);
+			raw_spin_unlock_irq(&x->wait.lock);
 			timeout = action(timeout);
-			spin_lock_irq(&x->wait.lock);
+			raw_spin_lock_irq(&x->wait.lock);
 		} while (!x->done && timeout);
-		__remove_wait_queue(&x->wait, &wait);
+		__finish_swait(&x->wait, &wait);
 		if (!x->done)
 			return timeout;
 	}
@@ -100,9 +102,9 @@ static inline long __sched
 
 	complete_acquire(x);
 
-	spin_lock_irq(&x->wait.lock);
+	raw_spin_lock_irq(&x->wait.lock);
 	timeout = do_wait_for_common(x, action, timeout, state);
-	spin_unlock_irq(&x->wait.lock);
+	raw_spin_unlock_irq(&x->wait.lock);
 
 	complete_release(x);
 
@@ -291,12 +293,12 @@ bool try_wait_for_completion(struct comp
 	if (!READ_ONCE(x->done))
 		return false;
 
-	spin_lock_irqsave(&x->wait.lock, flags);
+	raw_spin_lock_irqsave(&x->wait.lock, flags);
 	if (!x->done)
 		ret = false;
 	else if (x->done != UINT_MAX)
 		x->done--;
-	spin_unlock_irqrestore(&x->wait.lock, flags);
+	raw_spin_unlock_irqrestore(&x->wait.lock, flags);
 	return ret;
 }
 EXPORT_SYMBOL(try_wait_for_completion);
@@ -322,8 +324,8 @@ bool completion_done(struct completion *
 	 * otherwise we can end up freeing the completion before complete()
 	 * is done referencing it.
 	 */
-	spin_lock_irqsave(&x->wait.lock, flags);
-	spin_unlock_irqrestore(&x->wait.lock, flags);
+	raw_spin_lock_irqsave(&x->wait.lock, flags);
+	raw_spin_unlock_irqrestore(&x->wait.lock, flags);
 	return true;
 }
 EXPORT_SYMBOL(completion_done);



^ permalink raw reply	[flat|nested] 38+ messages in thread

* [patch V3 17/20] lockdep: Introduce wait-type checks
  2020-03-21 11:25 [patch V3 00/20] Lock ordering documentation and annotation for lockdep Thomas Gleixner
                   ` (15 preceding siblings ...)
  2020-03-21 11:26 ` [patch V3 16/20] completion: Use simple wait queues Thomas Gleixner
@ 2020-03-21 11:26 ` Thomas Gleixner
  2020-03-21 11:26 ` [patch V3 18/20] lockdep: Add hrtimer context tracing bits Thomas Gleixner
                   ` (3 subsequent siblings)
  20 siblings, 0 replies; 38+ messages in thread
From: Thomas Gleixner @ 2020-03-21 11:26 UTC (permalink / raw)
  To: LKML
  Cc: Peter Zijlstra, Ingo Molnar, Sebastian Siewior, Linus Torvalds,
	Joel Fernandes, Oleg Nesterov, Davidlohr Bueso, Logan Gunthorpe,
	Bjorn Helgaas, Kurt Schwemmer, linux-pci, Greg Kroah-Hartman,
	Felipe Balbi, linux-usb, Kalle Valo, David S. Miller,
	linux-wireless, netdev, Darren Hart, Andy Shevchenko,
	platform-driver-x86, Zhang Rui, Rafael J. Wysocki, linux-pm,
	Len Brown, linux-acpi, kbuild test robot, Nick Hu, Greentime Hu,
	Vincent Chen, Guo Ren, linux-csky, Brian Cain, linux-hexagon,
	Tony Luck, Fenghua Yu, linux-ia64, Michal Simek,
	Michael Ellerman, Arnd Bergmann, Geoff Levand, linuxppc-dev,
	Paul E . McKenney, Jonathan Corbet, Randy Dunlap,
	Davidlohr Bueso

From: Peter Zijlstra <peterz@infradead.org>

Extend lockdep to validate lock wait-type context.

The current wait-types are:

	LD_WAIT_FREE,		/* wait free, rcu etc.. */
	LD_WAIT_SPIN,		/* spin loops, raw_spinlock_t etc.. */
	LD_WAIT_CONFIG,		/* CONFIG_PREEMPT_LOCK, spinlock_t etc.. */
	LD_WAIT_SLEEP,		/* sleeping locks, mutex_t etc.. */

Where lockdep validates that the current lock (the one being acquired)
fits in the current wait-context (as generated by the held stack).

This ensures that there is no attempt to acquire mutexes while holding
spinlocks, to acquire spinlocks while holding raw_spinlocks and so on. In
other words, its a more fancy might_sleep().

Obviously RCU made the entire ordeal more complex than a simple single
value test because RCU can be acquired in (pretty much) any context and
while it presents a context to nested locks it is not the same as it
got acquired in.

Therefore its necessary to split the wait_type into two values, one
representing the acquire (outer) and one representing the nested context
(inner). For most 'normal' locks these two are the same.

[ To make static initialization easier we have the rule that:
  .outer == INV means .outer == .inner; because INV == 0. ]

It further means that its required to find the minimal .inner of the held
stack to compare against the outer of the new lock; because while 'normal'
RCU presents a CONFIG type to nested locks, if it is taken while already
holding a SPIN type it obviously doesn't relax the rules.

Below is an example output generated by the trivial test code:

  raw_spin_lock(&foo);
  spin_lock(&bar);
  spin_unlock(&bar);
  raw_spin_unlock(&foo);

 [ BUG: Invalid wait context ]
 -----------------------------
 swapper/0/1 is trying to lock:
 ffffc90000013f20 (&bar){....}-{3:3}, at: kernel_init+0xdb/0x187
 other info that might help us debug this:
 1 lock held by swapper/0/1:
  #0: ffffc90000013ee0 (&foo){+.+.}-{2:2}, at: kernel_init+0xd1/0x187

The way to read it is to look at the new -{n,m} part in the lock
description; -{3:3} for the attempted lock, and try and match that up to
the held locks, which in this case is the one: -{2,2}.

This tells that the acquiring lock requires a more relaxed environment than
presented by the lock stack.

Currently only the normal locks and RCU are converted, the rest of the
lockdep users defaults to .inner = INV which is ignored. More conversions
can be done when desired.

The check for spinlock_t nesting is not enabled by default. It's a separate
config option for now as there are known problems which are currently
addressed. The config option allows to identify these problems and to
verify that the solutions found are indeed solving them.

The config switch will be removed and the checks will permanently enabled
once the vast majority of issues has been addressed.

[ bigeasy: Move LD_WAIT_FREE,… out of CONFIG_LOCKDEP to avoid compile
	   failure with CONFIG_DEBUG_SPINLOCK + !CONFIG_LOCKDEP]
[ tglx: Add the config option ]

Requested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
V2: Fix the LOCKDEP=y && LOCK_PROVE=n case
---
 include/linux/irqflags.h        |    8 ++
 include/linux/lockdep.h         |   71 +++++++++++++++++---
 include/linux/mutex.h           |    7 +-
 include/linux/rwlock_types.h    |    6 +
 include/linux/rwsem.h           |    6 +
 include/linux/sched.h           |    1 
 include/linux/spinlock.h        |   35 +++++++---
 include/linux/spinlock_types.h  |   24 +++++-
 kernel/irq/handle.c             |    7 ++
 kernel/locking/lockdep.c        |  138 ++++++++++++++++++++++++++++++++++++++--
 kernel/locking/mutex-debug.c    |    2 
 kernel/locking/rwsem.c          |    2 
 kernel/locking/spinlock_debug.c |    6 -
 kernel/rcu/update.c             |   24 +++++-
 lib/Kconfig.debug               |   17 ++++
 15 files changed, 307 insertions(+), 47 deletions(-)

--- a/include/linux/irqflags.h
+++ b/include/linux/irqflags.h
@@ -37,7 +37,12 @@
 # define trace_softirqs_enabled(p)	((p)->softirqs_enabled)
 # define trace_hardirq_enter()			\
 do {						\
-	current->hardirq_context++;		\
+	if (!current->hardirq_context++)	\
+		current->hardirq_threaded = 0;	\
+} while (0)
+# define trace_hardirq_threaded()		\
+do {						\
+	current->hardirq_threaded = 1;		\
 } while (0)
 # define trace_hardirq_exit()			\
 do {						\
@@ -59,6 +64,7 @@ do {						\
 # define trace_hardirqs_enabled(p)	0
 # define trace_softirqs_enabled(p)	0
 # define trace_hardirq_enter()		do { } while (0)
+# define trace_hardirq_threaded()	do { } while (0)
 # define trace_hardirq_exit()		do { } while (0)
 # define lockdep_softirq_enter()	do { } while (0)
 # define lockdep_softirq_exit()		do { } while (0)
--- a/include/linux/lockdep.h
+++ b/include/linux/lockdep.h
@@ -21,6 +21,22 @@ extern int lock_stat;
 
 #include <linux/types.h>
 
+enum lockdep_wait_type {
+	LD_WAIT_INV = 0,	/* not checked, catch all */
+
+	LD_WAIT_FREE,		/* wait free, rcu etc.. */
+	LD_WAIT_SPIN,		/* spin loops, raw_spinlock_t etc.. */
+
+#ifdef CONFIG_PROVE_RAW_LOCK_NESTING
+	LD_WAIT_CONFIG,		/* CONFIG_PREEMPT_LOCK, spinlock_t etc.. */
+#else
+	LD_WAIT_CONFIG = LD_WAIT_SPIN,
+#endif
+	LD_WAIT_SLEEP,		/* sleeping locks, mutex_t etc.. */
+
+	LD_WAIT_MAX,		/* must be last */
+};
+
 #ifdef CONFIG_LOCKDEP
 
 #include <linux/linkage.h>
@@ -111,6 +127,9 @@ struct lock_class {
 	int				name_version;
 	const char			*name;
 
+	short				wait_type_inner;
+	short				wait_type_outer;
+
 #ifdef CONFIG_LOCK_STAT
 	unsigned long			contention_point[LOCKSTAT_POINTS];
 	unsigned long			contending_point[LOCKSTAT_POINTS];
@@ -158,6 +177,8 @@ struct lockdep_map {
 	struct lock_class_key		*key;
 	struct lock_class		*class_cache[NR_LOCKDEP_CACHING_CLASSES];
 	const char			*name;
+	short				wait_type_outer; /* can be taken in this context */
+	short				wait_type_inner; /* presents this context */
 #ifdef CONFIG_LOCK_STAT
 	int				cpu;
 	unsigned long			ip;
@@ -299,8 +320,21 @@ extern void lockdep_unregister_key(struc
  * to lockdep:
  */
 
-extern void lockdep_init_map(struct lockdep_map *lock, const char *name,
-			     struct lock_class_key *key, int subclass);
+extern void lockdep_init_map_waits(struct lockdep_map *lock, const char *name,
+	struct lock_class_key *key, int subclass, short inner, short outer);
+
+static inline void
+lockdep_init_map_wait(struct lockdep_map *lock, const char *name,
+		      struct lock_class_key *key, int subclass, short inner)
+{
+	lockdep_init_map_waits(lock, name, key, subclass, inner, LD_WAIT_INV);
+}
+
+static inline void lockdep_init_map(struct lockdep_map *lock, const char *name,
+			     struct lock_class_key *key, int subclass)
+{
+	lockdep_init_map_wait(lock, name, key, subclass, LD_WAIT_INV);
+}
 
 /*
  * Reinitialize a lock key - for cases where there is special locking or
@@ -308,18 +342,29 @@ extern void lockdep_init_map(struct lock
  * of dependencies wrong: they are either too broad (they need a class-split)
  * or they are too narrow (they suffer from a false class-split):
  */
-#define lockdep_set_class(lock, key) \
-		lockdep_init_map(&(lock)->dep_map, #key, key, 0)
-#define lockdep_set_class_and_name(lock, key, name) \
-		lockdep_init_map(&(lock)->dep_map, name, key, 0)
-#define lockdep_set_class_and_subclass(lock, key, sub) \
-		lockdep_init_map(&(lock)->dep_map, #key, key, sub)
-#define lockdep_set_subclass(lock, sub)	\
-		lockdep_init_map(&(lock)->dep_map, #lock, \
-				 (lock)->dep_map.key, sub)
+#define lockdep_set_class(lock, key)				\
+	lockdep_init_map_waits(&(lock)->dep_map, #key, key, 0,	\
+			       (lock)->dep_map.wait_type_inner,	\
+			       (lock)->dep_map.wait_type_outer)
+
+#define lockdep_set_class_and_name(lock, key, name)		\
+	lockdep_init_map_waits(&(lock)->dep_map, name, key, 0,	\
+			       (lock)->dep_map.wait_type_inner,	\
+			       (lock)->dep_map.wait_type_outer)
+
+#define lockdep_set_class_and_subclass(lock, key, sub)		\
+	lockdep_init_map_waits(&(lock)->dep_map, #key, key, sub,\
+			       (lock)->dep_map.wait_type_inner,	\
+			       (lock)->dep_map.wait_type_outer)
+
+#define lockdep_set_subclass(lock, sub)					\
+	lockdep_init_map_waits(&(lock)->dep_map, #lock, (lock)->dep_map.key, sub,\
+			       (lock)->dep_map.wait_type_inner,		\
+			       (lock)->dep_map.wait_type_outer)
 
 #define lockdep_set_novalidate_class(lock) \
 	lockdep_set_class_and_name(lock, &__lockdep_no_validate__, #lock)
+
 /*
  * Compare locking classes
  */
@@ -432,6 +477,10 @@ static inline void lockdep_set_selftest_
 # define lock_set_class(l, n, k, s, i)		do { } while (0)
 # define lock_set_subclass(l, s, i)		do { } while (0)
 # define lockdep_init()				do { } while (0)
+# define lockdep_init_map_waits(lock, name, key, sub, inner, outer) \
+		do { (void)(name); (void)(key); } while (0)
+# define lockdep_init_map_wait(lock, name, key, sub, inner) \
+		do { (void)(name); (void)(key); } while (0)
 # define lockdep_init_map(lock, name, key, sub) \
 		do { (void)(name); (void)(key); } while (0)
 # define lockdep_set_class(lock, key)		do { (void)(key); } while (0)
--- a/include/linux/mutex.h
+++ b/include/linux/mutex.h
@@ -109,8 +109,11 @@ do {									\
 } while (0)
 
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
-# define __DEP_MAP_MUTEX_INITIALIZER(lockname) \
-		, .dep_map = { .name = #lockname }
+# define __DEP_MAP_MUTEX_INITIALIZER(lockname)			\
+		, .dep_map = {					\
+			.name = #lockname,			\
+			.wait_type_inner = LD_WAIT_SLEEP,	\
+		}
 #else
 # define __DEP_MAP_MUTEX_INITIALIZER(lockname)
 #endif
--- a/include/linux/rwlock_types.h
+++ b/include/linux/rwlock_types.h
@@ -22,7 +22,11 @@ typedef struct {
 #define RWLOCK_MAGIC		0xdeaf1eed
 
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
-# define RW_DEP_MAP_INIT(lockname)	.dep_map = { .name = #lockname }
+# define RW_DEP_MAP_INIT(lockname)					\
+	.dep_map = {							\
+		.name = #lockname,					\
+		.wait_type_inner = LD_WAIT_CONFIG,			\
+	}
 #else
 # define RW_DEP_MAP_INIT(lockname)
 #endif
--- a/include/linux/rwsem.h
+++ b/include/linux/rwsem.h
@@ -71,7 +71,11 @@ static inline int rwsem_is_locked(struct
 /* Common initializer macros and functions */
 
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
-# define __RWSEM_DEP_MAP_INIT(lockname) , .dep_map = { .name = #lockname }
+# define __RWSEM_DEP_MAP_INIT(lockname)			\
+	, .dep_map = {					\
+		.name = #lockname,			\
+		.wait_type_inner = LD_WAIT_SLEEP,	\
+	}
 #else
 # define __RWSEM_DEP_MAP_INIT(lockname)
 #endif
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -970,6 +970,7 @@ struct task_struct {
 
 #ifdef CONFIG_TRACE_IRQFLAGS
 	unsigned int			irq_events;
+	unsigned int			hardirq_threaded;
 	unsigned long			hardirq_enable_ip;
 	unsigned long			hardirq_disable_ip;
 	unsigned int			hardirq_enable_event;
--- a/include/linux/spinlock.h
+++ b/include/linux/spinlock.h
@@ -93,12 +93,13 @@
 
 #ifdef CONFIG_DEBUG_SPINLOCK
   extern void __raw_spin_lock_init(raw_spinlock_t *lock, const char *name,
-				   struct lock_class_key *key);
-# define raw_spin_lock_init(lock)				\
-do {								\
-	static struct lock_class_key __key;			\
-								\
-	__raw_spin_lock_init((lock), #lock, &__key);		\
+				   struct lock_class_key *key, short inner);
+
+# define raw_spin_lock_init(lock)					\
+do {									\
+	static struct lock_class_key __key;				\
+									\
+	__raw_spin_lock_init((lock), #lock, &__key, LD_WAIT_SPIN);	\
 } while (0)
 
 #else
@@ -327,12 +328,26 @@ static __always_inline raw_spinlock_t *s
 	return &lock->rlock;
 }
 
-#define spin_lock_init(_lock)				\
-do {							\
-	spinlock_check(_lock);				\
-	raw_spin_lock_init(&(_lock)->rlock);		\
+#ifdef CONFIG_DEBUG_SPINLOCK
+
+# define spin_lock_init(lock)					\
+do {								\
+	static struct lock_class_key __key;			\
+								\
+	__raw_spin_lock_init(spinlock_check(lock),		\
+			     #lock, &__key, LD_WAIT_CONFIG);	\
+} while (0)
+
+#else
+
+# define spin_lock_init(_lock)			\
+do {						\
+	spinlock_check(_lock);			\
+	*(_lock) = __SPIN_LOCK_UNLOCKED(_lock);	\
 } while (0)
 
+#endif
+
 static __always_inline void spin_lock(spinlock_t *lock)
 {
 	raw_spin_lock(&lock->rlock);
--- a/include/linux/spinlock_types.h
+++ b/include/linux/spinlock_types.h
@@ -33,8 +33,18 @@ typedef struct raw_spinlock {
 #define SPINLOCK_OWNER_INIT	((void *)-1L)
 
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
-# define SPIN_DEP_MAP_INIT(lockname)	.dep_map = { .name = #lockname }
+# define RAW_SPIN_DEP_MAP_INIT(lockname)		\
+	.dep_map = {					\
+		.name = #lockname,			\
+		.wait_type_inner = LD_WAIT_SPIN,	\
+	}
+# define SPIN_DEP_MAP_INIT(lockname)			\
+	.dep_map = {					\
+		.name = #lockname,			\
+		.wait_type_inner = LD_WAIT_CONFIG,	\
+	}
 #else
+# define RAW_SPIN_DEP_MAP_INIT(lockname)
 # define SPIN_DEP_MAP_INIT(lockname)
 #endif
 
@@ -51,7 +61,7 @@ typedef struct raw_spinlock {
 	{					\
 	.raw_lock = __ARCH_SPIN_LOCK_UNLOCKED,	\
 	SPIN_DEBUG_INIT(lockname)		\
-	SPIN_DEP_MAP_INIT(lockname) }
+	RAW_SPIN_DEP_MAP_INIT(lockname) }
 
 #define __RAW_SPIN_LOCK_UNLOCKED(lockname)	\
 	(raw_spinlock_t) __RAW_SPIN_LOCK_INITIALIZER(lockname)
@@ -72,11 +82,17 @@ typedef struct spinlock {
 	};
 } spinlock_t;
 
+#define ___SPIN_LOCK_INITIALIZER(lockname)	\
+	{					\
+	.raw_lock = __ARCH_SPIN_LOCK_UNLOCKED,	\
+	SPIN_DEBUG_INIT(lockname)		\
+	SPIN_DEP_MAP_INIT(lockname) }
+
 #define __SPIN_LOCK_INITIALIZER(lockname) \
-	{ { .rlock = __RAW_SPIN_LOCK_INITIALIZER(lockname) } }
+	{ { .rlock = ___SPIN_LOCK_INITIALIZER(lockname) } }
 
 #define __SPIN_LOCK_UNLOCKED(lockname) \
-	(spinlock_t ) __SPIN_LOCK_INITIALIZER(lockname)
+	(spinlock_t) __SPIN_LOCK_INITIALIZER(lockname)
 
 #define DEFINE_SPINLOCK(x)	spinlock_t x = __SPIN_LOCK_UNLOCKED(x)
 
--- a/kernel/irq/handle.c
+++ b/kernel/irq/handle.c
@@ -145,6 +145,13 @@ irqreturn_t __handle_irq_event_percpu(st
 	for_each_action_of_desc(desc, action) {
 		irqreturn_t res;
 
+		/*
+		 * If this IRQ would be threaded under force_irqthreads, mark it so.
+		 */
+		if (irq_settings_can_thread(desc) &&
+		    !(action->flags & (IRQF_NO_THREAD | IRQF_PERCPU | IRQF_ONESHOT)))
+			trace_hardirq_threaded();
+
 		trace_irq_handler_entry(irq, action);
 		res = action->handler(irq, action->dev_id);
 		trace_irq_handler_exit(irq, action, res);
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -653,7 +653,9 @@ static void print_lock_name(struct lock_
 
 	printk(KERN_CONT " (");
 	__print_lock_name(class);
-	printk(KERN_CONT "){%s}", usage);
+	printk(KERN_CONT "){%s}-{%hd:%hd}", usage,
+			class->wait_type_outer ?: class->wait_type_inner,
+			class->wait_type_inner);
 }
 
 static void print_lockdep_cache(struct lockdep_map *lock)
@@ -1230,6 +1232,8 @@ register_lock_class(struct lockdep_map *
 	WARN_ON_ONCE(!list_empty(&class->locks_before));
 	WARN_ON_ONCE(!list_empty(&class->locks_after));
 	class->name_version = count_matching_names(class);
+	class->wait_type_inner = lock->wait_type_inner;
+	class->wait_type_outer = lock->wait_type_outer;
 	/*
 	 * We use RCU's safe list-add method to make
 	 * parallel walking of the hash-list safe:
@@ -3682,6 +3686,113 @@ static int mark_lock(struct task_struct
 	return ret;
 }
 
+static int
+print_lock_invalid_wait_context(struct task_struct *curr,
+				struct held_lock *hlock)
+{
+	if (!debug_locks_off())
+		return 0;
+	if (debug_locks_silent)
+		return 0;
+
+	pr_warn("\n");
+	pr_warn("=============================\n");
+	pr_warn("[ BUG: Invalid wait context ]\n");
+	print_kernel_ident();
+	pr_warn("-----------------------------\n");
+
+	pr_warn("%s/%d is trying to lock:\n", curr->comm, task_pid_nr(curr));
+	print_lock(hlock);
+
+	pr_warn("other info that might help us debug this:\n");
+	lockdep_print_held_locks(curr);
+
+	pr_warn("stack backtrace:\n");
+	dump_stack();
+
+	return 0;
+}
+
+/*
+ * Verify the wait_type context.
+ *
+ * This check validates we takes locks in the right wait-type order; that is it
+ * ensures that we do not take mutexes inside spinlocks and do not attempt to
+ * acquire spinlocks inside raw_spinlocks and the sort.
+ *
+ * The entire thing is slightly more complex because of RCU, RCU is a lock that
+ * can be taken from (pretty much) any context but also has constraints.
+ * However when taken in a stricter environment the RCU lock does not loosen
+ * the constraints.
+ *
+ * Therefore we must look for the strictest environment in the lock stack and
+ * compare that to the lock we're trying to acquire.
+ */
+static int check_wait_context(struct task_struct *curr, struct held_lock *next)
+{
+	short next_inner = hlock_class(next)->wait_type_inner;
+	short next_outer = hlock_class(next)->wait_type_outer;
+	short curr_inner;
+	int depth;
+
+	if (!curr->lockdep_depth || !next_inner || next->trylock)
+		return 0;
+
+	if (!next_outer)
+		next_outer = next_inner;
+
+	/*
+	 * Find start of current irq_context..
+	 */
+	for (depth = curr->lockdep_depth - 1; depth >= 0; depth--) {
+		struct held_lock *prev = curr->held_locks + depth;
+		if (prev->irq_context != next->irq_context)
+			break;
+	}
+	depth++;
+
+	/*
+	 * Set appropriate wait type for the context; for IRQs we have to take
+	 * into account force_irqthread as that is implied by PREEMPT_RT.
+	 */
+	if (curr->hardirq_context) {
+		/*
+		 * Check if force_irqthreads will run us threaded.
+		 */
+		if (curr->hardirq_threaded)
+			curr_inner = LD_WAIT_CONFIG;
+		else
+			curr_inner = LD_WAIT_SPIN;
+	} else if (curr->softirq_context) {
+		/*
+		 * Softirqs are always threaded.
+		 */
+		curr_inner = LD_WAIT_CONFIG;
+	} else {
+		curr_inner = LD_WAIT_MAX;
+	}
+
+	for (; depth < curr->lockdep_depth; depth++) {
+		struct held_lock *prev = curr->held_locks + depth;
+		short prev_inner = hlock_class(prev)->wait_type_inner;
+
+		if (prev_inner) {
+			/*
+			 * We can have a bigger inner than a previous one
+			 * when outer is smaller than inner, as with RCU.
+			 *
+			 * Also due to trylocks.
+			 */
+			curr_inner = min(curr_inner, prev_inner);
+		}
+	}
+
+	if (next_outer > curr_inner)
+		return print_lock_invalid_wait_context(curr, next);
+
+	return 0;
+}
+
 #else /* CONFIG_PROVE_LOCKING */
 
 static inline int
@@ -3701,13 +3812,20 @@ static inline int separate_irq_context(s
 	return 0;
 }
 
+static inline int check_wait_context(struct task_struct *curr,
+				     struct held_lock *next)
+{
+	return 0;
+}
+
 #endif /* CONFIG_PROVE_LOCKING */
 
 /*
  * Initialize a lock instance's lock-class mapping info:
  */
-void lockdep_init_map(struct lockdep_map *lock, const char *name,
-		      struct lock_class_key *key, int subclass)
+void lockdep_init_map_waits(struct lockdep_map *lock, const char *name,
+			    struct lock_class_key *key, int subclass,
+			    short inner, short outer)
 {
 	int i;
 
@@ -3728,6 +3846,9 @@ void lockdep_init_map(struct lockdep_map
 
 	lock->name = name;
 
+	lock->wait_type_outer = outer;
+	lock->wait_type_inner = inner;
+
 	/*
 	 * No key, no joy, we need to hash something.
 	 */
@@ -3761,7 +3882,7 @@ void lockdep_init_map(struct lockdep_map
 		raw_local_irq_restore(flags);
 	}
 }
-EXPORT_SYMBOL_GPL(lockdep_init_map);
+EXPORT_SYMBOL_GPL(lockdep_init_map_waits);
 
 struct lock_class_key __lockdep_no_validate__;
 EXPORT_SYMBOL_GPL(__lockdep_no_validate__);
@@ -3862,7 +3983,7 @@ static int __lock_acquire(struct lockdep
 
 	class_idx = class - lock_classes;
 
-	if (depth) {
+	if (depth) { /* we're holding locks */
 		hlock = curr->held_locks + depth - 1;
 		if (hlock->class_idx == class_idx && nest_lock) {
 			if (!references)
@@ -3904,6 +4025,9 @@ static int __lock_acquire(struct lockdep
 #endif
 	hlock->pin_count = pin_count;
 
+	if (check_wait_context(curr, hlock))
+		return 0;
+
 	/* Initialize the lock usage bit */
 	if (!mark_usage(curr, hlock, check))
 		return 0;
@@ -4139,7 +4263,9 @@ static int
 		return 0;
 	}
 
-	lockdep_init_map(lock, name, key, 0);
+	lockdep_init_map_waits(lock, name, key, 0,
+			       lock->wait_type_inner,
+			       lock->wait_type_outer);
 	class = register_lock_class(lock, subclass, 0);
 	hlock->class_idx = class - lock_classes;
 
--- a/kernel/locking/mutex-debug.c
+++ b/kernel/locking/mutex-debug.c
@@ -85,7 +85,7 @@ void debug_mutex_init(struct mutex *lock
 	 * Make sure we are not reinitializing a held lock:
 	 */
 	debug_check_no_locks_freed((void *)lock, sizeof(*lock));
-	lockdep_init_map(&lock->dep_map, name, key, 0);
+	lockdep_init_map_wait(&lock->dep_map, name, key, 0, LD_WAIT_SLEEP);
 #endif
 	lock->magic = lock;
 }
--- a/kernel/locking/rwsem.c
+++ b/kernel/locking/rwsem.c
@@ -329,7 +329,7 @@ void __init_rwsem(struct rw_semaphore *s
 	 * Make sure we are not reinitializing a held semaphore:
 	 */
 	debug_check_no_locks_freed((void *)sem, sizeof(*sem));
-	lockdep_init_map(&sem->dep_map, name, key, 0);
+	lockdep_init_map_wait(&sem->dep_map, name, key, 0, LD_WAIT_SLEEP);
 #endif
 #ifdef CONFIG_DEBUG_RWSEMS
 	sem->magic = sem;
--- a/kernel/locking/spinlock_debug.c
+++ b/kernel/locking/spinlock_debug.c
@@ -14,14 +14,14 @@
 #include <linux/export.h>
 
 void __raw_spin_lock_init(raw_spinlock_t *lock, const char *name,
-			  struct lock_class_key *key)
+			  struct lock_class_key *key, short inner)
 {
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 	/*
 	 * Make sure we are not reinitializing a held lock:
 	 */
 	debug_check_no_locks_freed((void *)lock, sizeof(*lock));
-	lockdep_init_map(&lock->dep_map, name, key, 0);
+	lockdep_init_map_wait(&lock->dep_map, name, key, 0, inner);
 #endif
 	lock->raw_lock = (arch_spinlock_t)__ARCH_SPIN_LOCK_UNLOCKED;
 	lock->magic = SPINLOCK_MAGIC;
@@ -39,7 +39,7 @@ void __rwlock_init(rwlock_t *lock, const
 	 * Make sure we are not reinitializing a held lock:
 	 */
 	debug_check_no_locks_freed((void *)lock, sizeof(*lock));
-	lockdep_init_map(&lock->dep_map, name, key, 0);
+	lockdep_init_map_wait(&lock->dep_map, name, key, 0, LD_WAIT_CONFIG);
 #endif
 	lock->raw_lock = (arch_rwlock_t) __ARCH_RW_LOCK_UNLOCKED;
 	lock->magic = RWLOCK_MAGIC;
--- a/kernel/rcu/update.c
+++ b/kernel/rcu/update.c
@@ -227,18 +227,30 @@ core_initcall(rcu_set_runtime_mode);
 
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 static struct lock_class_key rcu_lock_key;
-struct lockdep_map rcu_lock_map =
-	STATIC_LOCKDEP_MAP_INIT("rcu_read_lock", &rcu_lock_key);
+struct lockdep_map rcu_lock_map = {
+	.name = "rcu_read_lock",
+	.key = &rcu_lock_key,
+	.wait_type_outer = LD_WAIT_FREE,
+	.wait_type_inner = LD_WAIT_CONFIG, /* XXX PREEMPT_RCU ? */
+};
 EXPORT_SYMBOL_GPL(rcu_lock_map);
 
 static struct lock_class_key rcu_bh_lock_key;
-struct lockdep_map rcu_bh_lock_map =
-	STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_bh", &rcu_bh_lock_key);
+struct lockdep_map rcu_bh_lock_map = {
+	.name = "rcu_read_lock_bh",
+	.key = &rcu_bh_lock_key,
+	.wait_type_outer = LD_WAIT_FREE,
+	.wait_type_inner = LD_WAIT_CONFIG, /* PREEMPT_LOCK also makes BH preemptible */
+};
 EXPORT_SYMBOL_GPL(rcu_bh_lock_map);
 
 static struct lock_class_key rcu_sched_lock_key;
-struct lockdep_map rcu_sched_lock_map =
-	STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_sched", &rcu_sched_lock_key);
+struct lockdep_map rcu_sched_lock_map = {
+	.name = "rcu_read_lock_sched",
+	.key = &rcu_sched_lock_key,
+	.wait_type_outer = LD_WAIT_FREE,
+	.wait_type_inner = LD_WAIT_SPIN,
+};
 EXPORT_SYMBOL_GPL(rcu_sched_lock_map);
 
 static struct lock_class_key rcu_callback_key;
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -1086,6 +1086,23 @@ config PROVE_LOCKING
 
 	 For more details, see Documentation/locking/lockdep-design.rst.
 
+config PROVE_RAW_LOCK_NESTING
+	bool "Enable raw_spinlock - spinlock nesting checks"
+	depends on PROVE_LOCKING
+	default n
+	help
+	 Enable the raw_spinlock vs. spinlock nesting checks which ensure
+	 that the lock nesting rules for PREEMPT_RT enabled kernels are
+	 not violated.
+
+	 NOTE: There are known nesting problems. So if you enable this
+	 option expect lockdep splats until these problems have been fully
+	 addressed which is work in progress. This config switch allows to
+	 identify and analyze these problems. It will be removed and the
+	 check permanentely enabled once the main issues have been fixed.
+
+	 If unsure, select N.
+
 config LOCK_STAT
 	bool "Lock usage statistics"
 	depends on DEBUG_KERNEL && LOCK_DEBUGGING_SUPPORT


^ permalink raw reply	[flat|nested] 38+ messages in thread

* [patch V3 18/20] lockdep: Add hrtimer context tracing bits
  2020-03-21 11:25 [patch V3 00/20] Lock ordering documentation and annotation for lockdep Thomas Gleixner
                   ` (16 preceding siblings ...)
  2020-03-21 11:26 ` [patch V3 17/20] lockdep: Introduce wait-type checks Thomas Gleixner
@ 2020-03-21 11:26 ` Thomas Gleixner
  2020-03-21 11:26 ` [patch V3 19/20] lockdep: Annotate irq_work Thomas Gleixner
                   ` (2 subsequent siblings)
  20 siblings, 0 replies; 38+ messages in thread
From: Thomas Gleixner @ 2020-03-21 11:26 UTC (permalink / raw)
  To: LKML
  Cc: Peter Zijlstra, Ingo Molnar, Sebastian Siewior, Linus Torvalds,
	Joel Fernandes, Oleg Nesterov, Davidlohr Bueso, Logan Gunthorpe,
	Bjorn Helgaas, Kurt Schwemmer, linux-pci, Greg Kroah-Hartman,
	Felipe Balbi, linux-usb, Kalle Valo, David S. Miller,
	linux-wireless, netdev, Darren Hart, Andy Shevchenko,
	platform-driver-x86, Zhang Rui, Rafael J. Wysocki, linux-pm,
	Len Brown, linux-acpi, kbuild test robot, Nick Hu, Greentime Hu,
	Vincent Chen, Guo Ren, linux-csky, Brian Cain, linux-hexagon,
	Tony Luck, Fenghua Yu, linux-ia64, Michal Simek,
	Michael Ellerman, Arnd Bergmann, Geoff Levand, linuxppc-dev,
	Paul E . McKenney, Jonathan Corbet, Randy Dunlap,
	Davidlohr Bueso

From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

Set current->irq_config = 1 for hrtimers which are not marked to expire in
hard interrupt context during hrtimer_init(). These timers will expire in
softirq context on PREEMPT_RT.

Setting this allows lockdep to differentiate these timers. If a timer is
marked to expire in hard interrupt context then the timer callback is not
supposed to acquire a regular spinlock instead of a raw_spinlock in the
expiry callback.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
 include/linux/irqflags.h |   15 +++++++++++++++
 include/linux/sched.h    |    1 +
 kernel/locking/lockdep.c |    2 +-
 kernel/time/hrtimer.c    |    6 +++++-
 4 files changed, 22 insertions(+), 2 deletions(-)

--- a/include/linux/irqflags.h
+++ b/include/linux/irqflags.h
@@ -56,6 +56,19 @@ do {						\
 do {						\
 	current->softirq_context--;		\
 } while (0)
+
+# define lockdep_hrtimer_enter(__hrtimer)		\
+	  do {						\
+		  if (!__hrtimer->is_hard)		\
+			current->irq_config = 1;	\
+	  } while (0)
+
+# define lockdep_hrtimer_exit(__hrtimer)		\
+	  do {						\
+		  if (!__hrtimer->is_hard)		\
+			current->irq_config = 0;	\
+	  } while (0)
+
 #else
 # define trace_hardirqs_on()		do { } while (0)
 # define trace_hardirqs_off()		do { } while (0)
@@ -68,6 +81,8 @@ do {						\
 # define trace_hardirq_exit()		do { } while (0)
 # define lockdep_softirq_enter()	do { } while (0)
 # define lockdep_softirq_exit()		do { } while (0)
+# define lockdep_hrtimer_enter(__hrtimer)		do { } while (0)
+# define lockdep_hrtimer_exit(__hrtimer)		do { } while (0)
 #endif
 
 #if defined(CONFIG_IRQSOFF_TRACER) || \
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -983,6 +983,7 @@ struct task_struct {
 	unsigned int			softirq_enable_event;
 	int				softirqs_enabled;
 	int				softirq_context;
+	int				irq_config;
 #endif
 
 #ifdef CONFIG_LOCKDEP
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -3759,7 +3759,7 @@ static int check_wait_context(struct tas
 		/*
 		 * Check if force_irqthreads will run us threaded.
 		 */
-		if (curr->hardirq_threaded)
+		if (curr->hardirq_threaded || curr->irq_config)
 			curr_inner = LD_WAIT_CONFIG;
 		else
 			curr_inner = LD_WAIT_SPIN;
--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -1404,7 +1404,7 @@ static void __hrtimer_init(struct hrtime
 	base = softtimer ? HRTIMER_MAX_CLOCK_BASES / 2 : 0;
 	base += hrtimer_clockid_to_base(clock_id);
 	timer->is_soft = softtimer;
-	timer->is_hard = !softtimer;
+	timer->is_hard = !!(mode & HRTIMER_MODE_HARD);
 	timer->base = &cpu_base->clock_base[base];
 	timerqueue_init(&timer->node);
 }
@@ -1514,7 +1514,11 @@ static void __run_hrtimer(struct hrtimer
 	 */
 	raw_spin_unlock_irqrestore(&cpu_base->lock, flags);
 	trace_hrtimer_expire_entry(timer, now);
+	lockdep_hrtimer_enter(timer);
+
 	restart = fn(timer);
+
+	lockdep_hrtimer_exit(timer);
 	trace_hrtimer_expire_exit(timer);
 	raw_spin_lock_irq(&cpu_base->lock);
 



^ permalink raw reply	[flat|nested] 38+ messages in thread

* [patch V3 19/20] lockdep: Annotate irq_work
  2020-03-21 11:25 [patch V3 00/20] Lock ordering documentation and annotation for lockdep Thomas Gleixner
                   ` (17 preceding siblings ...)
  2020-03-21 11:26 ` [patch V3 18/20] lockdep: Add hrtimer context tracing bits Thomas Gleixner
@ 2020-03-21 11:26 ` Thomas Gleixner
  2020-03-21 11:26 ` [patch V3 20/20] lockdep: Add posixtimer context tracing bits Thomas Gleixner
  2020-03-21 17:19 ` [patch V3 00/20] Lock ordering documentation and annotation for lockdep Davidlohr Bueso
  20 siblings, 0 replies; 38+ messages in thread
From: Thomas Gleixner @ 2020-03-21 11:26 UTC (permalink / raw)
  To: LKML
  Cc: Peter Zijlstra, Ingo Molnar, Sebastian Siewior, Linus Torvalds,
	Joel Fernandes, Oleg Nesterov, Davidlohr Bueso, Logan Gunthorpe,
	Bjorn Helgaas, Kurt Schwemmer, linux-pci, Greg Kroah-Hartman,
	Felipe Balbi, linux-usb, Kalle Valo, David S. Miller,
	linux-wireless, netdev, Darren Hart, Andy Shevchenko,
	platform-driver-x86, Zhang Rui, Rafael J. Wysocki, linux-pm,
	Len Brown, linux-acpi, kbuild test robot, Nick Hu, Greentime Hu,
	Vincent Chen, Guo Ren, linux-csky, Brian Cain, linux-hexagon,
	Tony Luck, Fenghua Yu, linux-ia64, Michal Simek,
	Michael Ellerman, Arnd Bergmann, Geoff Levand, linuxppc-dev,
	Paul E . McKenney, Jonathan Corbet, Randy Dunlap,
	Davidlohr Bueso

From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

Mark irq_work items with IRQ_WORK_HARD_IRQ which should be invoked in
hardirq context even on PREEMPT_RT. IRQ_WORK without this flag will be
invoked in softirq context on PREEMPT_RT.

Set ->irq_config to 1 for the IRQ_WORK items which are invoked in softirq
context so lockdep knows that these can safely acquire a spinlock_t.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
 include/linux/irq_work.h |    2 ++
 include/linux/irqflags.h |   13 +++++++++++++
 kernel/irq_work.c        |    2 ++
 kernel/rcu/tree.c        |    1 +
 kernel/time/tick-sched.c |    1 +
 5 files changed, 19 insertions(+)

--- a/include/linux/irq_work.h
+++ b/include/linux/irq_work.h
@@ -18,6 +18,8 @@
 
 /* Doesn't want IPI, wait for tick: */
 #define IRQ_WORK_LAZY		BIT(2)
+/* Run hard IRQ context, even on RT */
+#define IRQ_WORK_HARD_IRQ	BIT(3)
 
 #define IRQ_WORK_CLAIMED	(IRQ_WORK_PENDING | IRQ_WORK_BUSY)
 
--- a/include/linux/irqflags.h
+++ b/include/linux/irqflags.h
@@ -69,6 +69,17 @@ do {						\
 			current->irq_config = 0;	\
 	  } while (0)
 
+# define lockdep_irq_work_enter(__work)					\
+	  do {								\
+		  if (!(atomic_read(&__work->flags) & IRQ_WORK_HARD_IRQ))\
+			current->irq_config = 1;			\
+	  } while (0)
+# define lockdep_irq_work_exit(__work)					\
+	  do {								\
+		  if (!(atomic_read(&__work->flags) & IRQ_WORK_HARD_IRQ))\
+			current->irq_config = 0;			\
+	  } while (0)
+
 #else
 # define trace_hardirqs_on()		do { } while (0)
 # define trace_hardirqs_off()		do { } while (0)
@@ -83,6 +94,8 @@ do {						\
 # define lockdep_softirq_exit()		do { } while (0)
 # define lockdep_hrtimer_enter(__hrtimer)		do { } while (0)
 # define lockdep_hrtimer_exit(__hrtimer)		do { } while (0)
+# define lockdep_irq_work_enter(__work)		do { } while (0)
+# define lockdep_irq_work_exit(__work)		do { } while (0)
 #endif
 
 #if defined(CONFIG_IRQSOFF_TRACER) || \
--- a/kernel/irq_work.c
+++ b/kernel/irq_work.c
@@ -153,7 +153,9 @@ static void irq_work_run_list(struct lli
 		 */
 		flags = atomic_fetch_andnot(IRQ_WORK_PENDING, &work->flags);
 
+		lockdep_irq_work_enter(work);
 		work->func(work);
+		lockdep_irq_work_exit(work);
 		/*
 		 * Clear the BUSY bit and return to the free state if
 		 * no-one else claimed it meanwhile.
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -1113,6 +1113,7 @@ static int rcu_implicit_dynticks_qs(stru
 		    !rdp->rcu_iw_pending && rdp->rcu_iw_gp_seq != rnp->gp_seq &&
 		    (rnp->ffmask & rdp->grpmask)) {
 			init_irq_work(&rdp->rcu_iw, rcu_iw_handler);
+			atomic_set(&rdp->rcu_iw.flags, IRQ_WORK_HARD_IRQ);
 			rdp->rcu_iw_pending = true;
 			rdp->rcu_iw_gp_seq = rnp->gp_seq;
 			irq_work_queue_on(&rdp->rcu_iw, rdp->cpu);
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -245,6 +245,7 @@ static void nohz_full_kick_func(struct i
 
 static DEFINE_PER_CPU(struct irq_work, nohz_full_kick_work) = {
 	.func = nohz_full_kick_func,
+	.flags = ATOMIC_INIT(IRQ_WORK_HARD_IRQ),
 };
 
 /*



^ permalink raw reply	[flat|nested] 38+ messages in thread

* [patch V3 20/20] lockdep: Add posixtimer context tracing bits
  2020-03-21 11:25 [patch V3 00/20] Lock ordering documentation and annotation for lockdep Thomas Gleixner
                   ` (18 preceding siblings ...)
  2020-03-21 11:26 ` [patch V3 19/20] lockdep: Annotate irq_work Thomas Gleixner
@ 2020-03-21 11:26 ` Thomas Gleixner
  2020-03-21 17:19 ` [patch V3 00/20] Lock ordering documentation and annotation for lockdep Davidlohr Bueso
  20 siblings, 0 replies; 38+ messages in thread
From: Thomas Gleixner @ 2020-03-21 11:26 UTC (permalink / raw)
  To: LKML
  Cc: Peter Zijlstra, Ingo Molnar, Sebastian Siewior, Linus Torvalds,
	Joel Fernandes, Oleg Nesterov, Davidlohr Bueso, Logan Gunthorpe,
	Bjorn Helgaas, Kurt Schwemmer, linux-pci, Greg Kroah-Hartman,
	Felipe Balbi, linux-usb, Kalle Valo, David S. Miller,
	linux-wireless, netdev, Darren Hart, Andy Shevchenko,
	platform-driver-x86, Zhang Rui, Rafael J. Wysocki, linux-pm,
	Len Brown, linux-acpi, kbuild test robot, Nick Hu, Greentime Hu,
	Vincent Chen, Guo Ren, linux-csky, Brian Cain, linux-hexagon,
	Tony Luck, Fenghua Yu, linux-ia64, Michal Simek,
	Michael Ellerman, Arnd Bergmann, Geoff Levand, linuxppc-dev,
	Paul E . McKenney, Jonathan Corbet, Randy Dunlap,
	Davidlohr Bueso

From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

Splitting run_posix_cpu_timers() into two parts is work in progress which
is stuck on other entry code related problems. The heavy lifting which
involves locking of sighand lock will be moved into task context so the
necessary execution time is burdened on the task and not on interrupt
context.

Until this work completes lockdep with the spinlock nesting rules enabled
would emit warnings for this known context.

Prevent it by setting "->irq_config = 1" for the invocation of
run_posix_cpu_timers() so lockdep does not complain when sighand lock is
acquried. This will be removed once the split is completed.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
 include/linux/irqflags.h       |   12 ++++++++++++
 kernel/time/posix-cpu-timers.c |    6 +++++-
 2 files changed, 17 insertions(+), 1 deletion(-)

--- a/include/linux/irqflags.h
+++ b/include/linux/irqflags.h
@@ -69,6 +69,16 @@ do {						\
 			current->irq_config = 0;	\
 	  } while (0)
 
+# define lockdep_posixtimer_enter()				\
+	  do {							\
+		  current->irq_config = 1;			\
+	  } while (0)
+
+# define lockdep_posixtimer_exit()				\
+	  do {							\
+		  current->irq_config = 0;			\
+	  } while (0)
+
 # define lockdep_irq_work_enter(__work)					\
 	  do {								\
 		  if (!(atomic_read(&__work->flags) & IRQ_WORK_HARD_IRQ))\
@@ -94,6 +104,8 @@ do {						\
 # define lockdep_softirq_exit()		do { } while (0)
 # define lockdep_hrtimer_enter(__hrtimer)		do { } while (0)
 # define lockdep_hrtimer_exit(__hrtimer)		do { } while (0)
+# define lockdep_posixtimer_enter()		do { } while (0)
+# define lockdep_posixtimer_exit()		do { } while (0)
 # define lockdep_irq_work_enter(__work)		do { } while (0)
 # define lockdep_irq_work_exit(__work)		do { } while (0)
 #endif
--- a/kernel/time/posix-cpu-timers.c
+++ b/kernel/time/posix-cpu-timers.c
@@ -1126,8 +1126,11 @@ void run_posix_cpu_timers(void)
 	if (!fastpath_timer_check(tsk))
 		return;
 
-	if (!lock_task_sighand(tsk, &flags))
+	lockdep_posixtimer_enter();
+	if (!lock_task_sighand(tsk, &flags)) {
+		lockdep_posixtimer_exit();
 		return;
+	}
 	/*
 	 * Here we take off tsk->signal->cpu_timers[N] and
 	 * tsk->cpu_timers[N] all the timers that are firing, and
@@ -1169,6 +1172,7 @@ void run_posix_cpu_timers(void)
 			cpu_timer_fire(timer);
 		spin_unlock(&timer->it_lock);
 	}
+	lockdep_posixtimer_exit();
 }
 
 /*


^ permalink raw reply	[flat|nested] 38+ messages in thread

* Re: [patch V3 12/20] powerpc/ps3: Convert half completion to rcuwait
  2020-03-21 11:25 ` [patch V3 12/20] powerpc/ps3: Convert half completion to rcuwait Thomas Gleixner
@ 2020-03-21 13:22   ` Thomas Gleixner
  2020-03-27 19:14   ` Geoff Levand
  1 sibling, 0 replies; 38+ messages in thread
From: Thomas Gleixner @ 2020-03-21 13:22 UTC (permalink / raw)
  To: LKML
  Cc: Peter Zijlstra, Ingo Molnar, Sebastian Siewior, Linus Torvalds,
	Joel Fernandes, Oleg Nesterov, Davidlohr Bueso, Michael Ellerman,
	Arnd Bergmann, Geoff Levand, linuxppc-dev, Logan Gunthorpe,
	Bjorn Helgaas, Kurt Schwemmer, linux-pci, Greg Kroah-Hartman,
	Felipe Balbi, linux-usb, Kalle Valo, David S. Miller,
	linux-wireless, netdev, Darren Hart, Andy Shevchenko,
	platform-driver-x86, Zhang Rui, Rafael J. Wysocki, linux-pm,
	Len Brown, linux-acpi, kbuild test robot, Nick Hu, Greentime Hu,
	Vincent Chen, Guo Ren, linux-csky, Brian Cain, linux-hexagon,
	Tony Luck, Fenghua Yu, linux-ia64, Michal Simek,
	Paul E . McKenney, Jonathan Corbet, Randy Dunlap,
	Davidlohr Bueso

Thomas Gleixner <tglx@linutronix.de> writes:

> From: Thomas Gleixner <tglx@linutronix.de>

That's obviously bogus and wants to be:

From: Peter Zijlstra (Intel) <peterz@infradead.org>


^ permalink raw reply	[flat|nested] 38+ messages in thread

* Re: [patch V3 00/20] Lock ordering documentation and annotation for lockdep
  2020-03-21 11:25 [patch V3 00/20] Lock ordering documentation and annotation for lockdep Thomas Gleixner
                   ` (19 preceding siblings ...)
  2020-03-21 11:26 ` [patch V3 20/20] lockdep: Add posixtimer context tracing bits Thomas Gleixner
@ 2020-03-21 17:19 ` Davidlohr Bueso
  2020-03-21 17:45   ` Thomas Gleixner
  20 siblings, 1 reply; 38+ messages in thread
From: Davidlohr Bueso @ 2020-03-21 17:19 UTC (permalink / raw)
  To: Thomas Gleixner
  Cc: LKML, Peter Zijlstra, Ingo Molnar, Sebastian Siewior,
	Linus Torvalds, Joel Fernandes, Oleg Nesterov, Logan Gunthorpe,
	Bjorn Helgaas, Kurt Schwemmer, linux-pci, Greg Kroah-Hartman,
	Felipe Balbi, linux-usb, Kalle Valo, David S. Miller,
	linux-wireless, netdev, Darren Hart, Andy Shevchenko,
	platform-driver-x86, Zhang Rui, Rafael J. Wysocki, linux-pm,
	Len Brown, linux-acpi, kbuild test robot, Nick Hu, Greentime Hu,
	Vincent Chen, Guo Ren, linux-csky, Brian Cain, linux-hexagon,
	Tony Luck, Fenghua Yu, linux-ia64, Michal Simek,
	Michael Ellerman, Arnd Bergmann, Geoff Levand, linuxppc-dev,
	Paul E . McKenney, Jonathan Corbet, Randy Dunlap,
	Davidlohr Bueso

On Sat, 21 Mar 2020, Thomas Gleixner wrote:

>This is the third and hopefully final version of this work. The second one
>can be found here:

Would you rather I send in a separate series with the kvm changes, or
should I just send a v2 with the fixes here again?

Thanks,
Davidlohr

^ permalink raw reply	[flat|nested] 38+ messages in thread

* Re: [patch V3 00/20] Lock ordering documentation and annotation for lockdep
  2020-03-21 17:19 ` [patch V3 00/20] Lock ordering documentation and annotation for lockdep Davidlohr Bueso
@ 2020-03-21 17:45   ` Thomas Gleixner
  0 siblings, 0 replies; 38+ messages in thread
From: Thomas Gleixner @ 2020-03-21 17:45 UTC (permalink / raw)
  To: Davidlohr Bueso
  Cc: LKML, Peter Zijlstra, Ingo Molnar, Sebastian Siewior,
	Linus Torvalds, Joel Fernandes, Oleg Nesterov, Logan Gunthorpe,
	Bjorn Helgaas, Kurt Schwemmer, linux-pci, Greg Kroah-Hartman,
	Felipe Balbi, linux-usb, Kalle Valo, David S. Miller,
	linux-wireless, netdev, Darren Hart, Andy Shevchenko,
	platform-driver-x86, Zhang Rui, Rafael J. Wysocki, linux-pm,
	Len Brown, linux-acpi, kbuild test robot, Nick Hu, Greentime Hu,
	Vincent Chen, Guo Ren, linux-csky, Brian Cain, linux-hexagon,
	Tony Luck, Fenghua Yu, linux-ia64, Michal Simek,
	Michael Ellerman, Arnd Bergmann, Geoff Levand, linuxppc-dev,
	Paul E . McKenney, Jonathan Corbet, Randy Dunlap,
	Davidlohr Bueso

Davidlohr Bueso <dave@stgolabs.net> writes:

> On Sat, 21 Mar 2020, Thomas Gleixner wrote:
>
>>This is the third and hopefully final version of this work. The second one
>>can be found here:
>
> Would you rather I send in a separate series with the kvm changes, or
> should I just send a v2 with the fixes here again?

Send a separate series please. These nested threads are hard to follow.

Thanks,

        tglx

^ permalink raw reply	[flat|nested] 38+ messages in thread

* Re: [patch V3 13/20] Documentation: Add lock ordering and nesting documentation
  2020-03-21 11:25 ` [patch V3 13/20] Documentation: Add lock ordering and nesting documentation Thomas Gleixner
@ 2020-03-23  2:55   ` Paul E. McKenney
  2020-03-24 23:13     ` Thomas Gleixner
  0 siblings, 1 reply; 38+ messages in thread
From: Paul E. McKenney @ 2020-03-23  2:55 UTC (permalink / raw)
  To: Thomas Gleixner
  Cc: LKML, Peter Zijlstra, Ingo Molnar, Sebastian Siewior,
	Linus Torvalds, Joel Fernandes, Oleg Nesterov, Davidlohr Bueso,
	Jonathan Corbet, Randy Dunlap, Logan Gunthorpe, Bjorn Helgaas,
	Kurt Schwemmer, linux-pci, Greg Kroah-Hartman, Felipe Balbi,
	linux-usb, Kalle Valo, David S. Miller, linux-wireless, netdev,
	Darren Hart, Andy Shevchenko, platform-driver-x86, Zhang Rui,
	Rafael J. Wysocki, linux-pm, Len Brown, linux-acpi,
	kbuild test robot, Nick Hu, Greentime Hu, Vincent Chen, Guo Ren,
	linux-csky, Brian Cain, linux-hexagon, Tony Luck, Fenghua Yu,
	linux-ia64, Michal Simek, Michael Ellerman, Arnd Bergmann,
	Geoff Levand, linuxppc-dev, Davidlohr Bueso

On Sat, Mar 21, 2020 at 12:25:57PM +0100, Thomas Gleixner wrote:
> From: Thomas Gleixner <tglx@linutronix.de>
> 
> The kernel provides a variety of locking primitives. The nesting of these
> lock types and the implications of them on RT enabled kernels is nowhere
> documented.
> 
> Add initial documentation.
> 
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> Cc: "Paul E . McKenney" <paulmck@kernel.org>
> Cc: Jonathan Corbet <corbet@lwn.net>
> Cc: Davidlohr Bueso <dave@stgolabs.net>
> Cc: Randy Dunlap <rdunlap@infradead.org>
> ---
> V3: Addressed review comments from Paul, Jonathan, Davidlohr
> V2: Addressed review comments from Randy
> ---
>  Documentation/locking/index.rst     |    1 
>  Documentation/locking/locktypes.rst |  299 ++++++++++++++++++++++++++++++++++++
>  2 files changed, 300 insertions(+)
>  create mode 100644 Documentation/locking/locktypes.rst
> 
> --- a/Documentation/locking/index.rst
> +++ b/Documentation/locking/index.rst
> @@ -7,6 +7,7 @@ locking
>  .. toctree::
>      :maxdepth: 1
>  
> +    locktypes
>      lockdep-design
>      lockstat
>      locktorture
> --- /dev/null
> +++ b/Documentation/locking/locktypes.rst
> @@ -0,0 +1,299 @@

[ . . . Adding your example execution sequences . . . ]

> +PREEMPT_RT kernels preserve all other spinlock_t semantics:
> +
> + - Tasks holding a spinlock_t do not migrate.  Non-PREEMPT_RT kernels
> +   avoid migration by disabling preemption.  PREEMPT_RT kernels instead
> +   disable migration, which ensures that pointers to per-CPU variables
> +   remain valid even if the task is preempted.
> +
> + - Task state is preserved across spinlock acquisition, ensuring that the
> +   task-state rules apply to all kernel configurations.  Non-PREEMPT_RT
> +   kernels leave task state untouched.  However, PREEMPT_RT must change
> +   task state if the task blocks during acquisition.  Therefore, it saves
> +   the current task state before blocking and the corresponding lock wakeup
> +   restores it.
> +
> +   Other types of wakeups would normally unconditionally set the task state
> +   to RUNNING, but that does not work here because the task must remain
> +   blocked until the lock becomes available.  Therefore, when a non-lock
> +   wakeup attempts to awaken a task blocked waiting for a spinlock, it
> +   instead sets the saved state to RUNNING.  Then, when the lock
> +   acquisition completes, the lock wakeup sets the task state to the saved
> +   state, in this case setting it to RUNNING.

In the normal case where the task sleeps through the entire lock
acquisition, the sequence of events is as follows:

     state = UNINTERRUPTIBLE
     lock()
       block()
         real_state = state
         state = SLEEPONLOCK

                               lock wakeup
                                 state = real_state == UNINTERRUPTIBLE

This sequence of events can occur when the task acquires spinlocks
on its way to sleeping, for example, in a call to wait_event().

The non-lock wakeup can occur when a wakeup races with this wait_event(),
which can result in the following sequence of events:

     state = UNINTERRUPTIBLE
     lock()
       block()
         real_state = state
         state = SLEEPONLOCK

                             non lock wakeup
                                 real_state = RUNNING

                               lock wakeup
                                 state = real_state == RUNNING

Without this real_state subterfuge, the wakeup might be lost.

[ . . . and continuing where I left off earlier . . . ]

> +bit spinlocks
> +-------------
> +
> +Bit spinlocks are problematic for PREEMPT_RT as they cannot be easily
> +substituted by an RT-mutex based implementation for obvious reasons.
> +
> +The semantics of bit spinlocks are preserved on PREEMPT_RT kernels and the
> +caveats vs. raw_spinlock_t apply.
> +
> +Some bit spinlocks are substituted by regular spinlock_t for PREEMPT_RT but
> +this requires conditional (#ifdef'ed) code changes at the usage site while
> +the spinlock_t substitution is simply done by the compiler and the
> +conditionals are restricted to header files and core implementation of the
> +locking primitives and the usage sites do not require any changes.

PREEMPT_RT cannot substitute bit spinlocks because a single bit is
too small to accommodate an RT-mutex.  Therefore, the semantics of bit
spinlocks are preserved on PREEMPT_RT kernels, so that the raw_spinlock_t
caveats also apply to bit spinlocks.

Some bit spinlocks are replaced with regular spinlock_t for PREEMPT_RT
using conditional (#ifdef'ed) code changes at the usage site.
In contrast, usage-site changes are not needed for the spinlock_t
substitution.  Instead, conditionals in header files and the core locking
implemementation enable the compiler to do the substitution transparently.


> +Lock type nesting rules
> +=======================
> +
> +The most basic rules are:
> +
> +  - Lock types of the same lock category (sleeping, spinning) can nest
> +    arbitrarily as long as they respect the general lock ordering rules to
> +    prevent deadlocks.

  - Lock types in the same category (sleeping, spinning) can nest
     arbitrarily as long as they respect the general deadlock-avoidance
     ordering rules.

[ Give or take lockdep eventually complaining about too-deep nesting,
  but that is probably not worth mentioning here.  Leave that caveat
  to the lockdep documentation. ]

> +  - Sleeping lock types cannot nest inside spinning lock types.
> +
> +  - Spinning lock types can nest inside sleeping lock types.
> +
> +These rules apply in general independent of CONFIG_PREEMPT_RT.

These constraints apply both in CONFIG_PREEMPT_RT and otherwise.

> +As PREEMPT_RT changes the lock category of spinlock_t and rwlock_t from
> +spinning to sleeping this has obviously restrictions how they can nest with
> +raw_spinlock_t.
> +
> +This results in the following nest ordering:

The fact that PREEMPT_RT changes the lock category of spinlock_t and
rwlock_t from spinning to sleeping means that they cannot be acquired
while holding a raw spinlock.  This results in the following nesting
ordering:

> +  1) Sleeping locks
> +  2) spinlock_t and rwlock_t
> +  3) raw_spinlock_t and bit spinlocks
> +
> +Lockdep is aware of these constraints to ensure that they are respected.

Lockdep will complain if these constraints are violated, both in
CONFIG_PREEMPT_RT and otherwise.


> +Owner semantics
> +===============
> +
> +Most lock types in the Linux kernel have strict owner semantics, i.e. the
> +context (task) which acquires a lock has to release it.

The aforementioned lock types have strict owner semantics: The context
(task) that acquired the lock must release it.

> +There are two exceptions:
> +
> +  - semaphores
> +  - rwsems
> +
> +semaphores have no owner semantics for historical reason, and as such
> +trylock and release operations can be called from any context. They are
> +often used for both serialization and waiting purposes. That's generally
> +discouraged and should be replaced by separate serialization and wait
> +mechanisms, such as mutexes and completions.

semaphores lack owner semantics for historical reasons, so their trylock
and release operations may be called from any context. They are often
used for both serialization and waiting, but new use cases should
instead use separate serialization and wait mechanisms, such as mutexes
and completions.

> +rwsems have grown interfaces which allow non owner release for special
> +purposes. This usage is problematic on PREEMPT_RT because PREEMPT_RT
> +substitutes all locking primitives except semaphores with RT-mutex based
> +implementations to provide priority inheritance for all lock types except
> +the truly spinning ones. Priority inheritance on ownerless locks is
> +obviously impossible.
> +
> +For now the rwsem non-owner release excludes code which utilizes it from
> +being used on PREEMPT_RT enabled kernels. In same cases this can be
> +mitigated by disabling portions of the code, in other cases the complete
> +functionality has to be disabled until a workable solution has been found.

rwsems have grown special-purpose interfaces that allow non-owner release.
This non-owner release prevents PREEMPT_RT from substituting RT-mutex
implementations, for example, by defeating priority inheritance.
After all, if the lock has no owner, whose priority should be boosted?
As a result, PREEMPT_RT does not currently support rwsem, which in turn
means that code using it must therefore be disabled until a workable
solution presents itself.

[ Note: Not as confident as I would like to be in the above. ]

							Thanx, Paul

^ permalink raw reply	[flat|nested] 38+ messages in thread

* [PATCH] completion: Use lockdep_assert_RT_in_threaded_ctx() in complete_all()
  2020-03-21 11:26 ` [patch V3 16/20] completion: Use simple wait queues Thomas Gleixner
@ 2020-03-23 15:20   ` Sebastian Siewior
  0 siblings, 0 replies; 38+ messages in thread
From: Sebastian Siewior @ 2020-03-23 15:20 UTC (permalink / raw)
  To: Thomas Gleixner
  Cc: LKML, Peter Zijlstra, Ingo Molnar, Linus Torvalds,
	Joel Fernandes, Oleg Nesterov, Davidlohr Bueso, Davidlohr Bueso,
	Greg Kroah-Hartman, Logan Gunthorpe, Bjorn Helgaas,
	Kurt Schwemmer, linux-pci, Felipe Balbi, linux-usb, Kalle Valo,
	David S. Miller, linux-wireless, netdev, Darren Hart,
	Andy Shevchenko, platform-driver-x86, Zhang Rui,
	Rafael J. Wysocki, linux-pm, Len Brown, linux-acpi,
	kbuild test robot, Nick Hu, Greentime Hu, Vincent Chen, Guo Ren,
	linux-csky, Brian Cain, linux-hexagon, Tony Luck, Fenghua Yu,
	linux-ia64, Michal Simek, Michael Ellerman, Arnd Bergmann,
	Geoff Levand, linuxppc-dev, Paul E . McKenney, Jonathan Corbet,
	Randy Dunlap

The warning was intended to spot complete_all() users from hardirq
context on PREEMPT_RT. The warning as-is will also trigger in interrupt
handlers, which are threaded on PREEMPT_RT, which was not intended.

Use lockdep_assert_RT_in_threaded_ctx() which triggers in non-preemptive
context on PREEMPT_RT.

Suggested-by: Peter Zijlstra <peterz@infradead.org>
Reported-by: kernel test robot <rong.a.chen@intel.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 include/linux/lockdep.h   | 15 +++++++++++++++
 kernel/sched/completion.c |  2 +-
 2 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
index 425b4ceb7cd07..206774ac69460 100644
--- a/include/linux/lockdep.h
+++ b/include/linux/lockdep.h
@@ -711,6 +711,21 @@ do {									\
 # define lockdep_assert_in_irq() do { } while (0)
 #endif
 
+#ifdef CONFIG_PROVE_RAW_LOCK_NESTING
+
+# define lockdep_assert_RT_in_threaded_ctx() do {			\
+		WARN_ONCE(debug_locks && !current->lockdep_recursion &&	\
+			  current->hardirq_context &&			\
+			  !(current->hardirq_threaded || current->irq_config),	\
+			  "Not in threaded context on PREEMPT_RT as expected\n");	\
+} while (0)
+
+#else
+
+# define lockdep_assert_RT_in_threaded_ctx() do { } while (0)
+
+#endif
+
 #ifdef CONFIG_LOCKDEP
 void lockdep_rcu_suspicious(const char *file, const int line, const char *s);
 #else
diff --git a/kernel/sched/completion.c b/kernel/sched/completion.c
index f15e96164ff1e..a778554f9dad7 100644
--- a/kernel/sched/completion.c
+++ b/kernel/sched/completion.c
@@ -58,7 +58,7 @@ void complete_all(struct completion *x)
 {
 	unsigned long flags;
 
-	WARN_ON(irqs_disabled());
+	lockdep_assert_RT_in_threaded_ctx();
 
 	raw_spin_lock_irqsave(&x->wait.lock, flags);
 	x->done = UINT_MAX;
-- 
2.26.0.rc2


^ permalink raw reply	[flat|nested] 38+ messages in thread

* RE: [patch V3 08/20] hexagon: Remove mm.h from asm/uaccess.h
  2020-03-21 11:25 ` [patch V3 08/20] hexagon: " Thomas Gleixner
@ 2020-03-23 21:46   ` Brian Cain
  0 siblings, 0 replies; 38+ messages in thread
From: Brian Cain @ 2020-03-23 21:46 UTC (permalink / raw)
  To: 'Thomas Gleixner', 'LKML'
  Cc: 'Peter Zijlstra', 'Ingo Molnar',
	'Sebastian Siewior', 'Linus Torvalds',
	'Joel Fernandes', 'Oleg Nesterov',
	'Davidlohr Bueso', 'kbuild test robot',
	linux-hexagon, 'Logan Gunthorpe', 'Bjorn Helgaas',
	'Kurt Schwemmer', linux-pci, 'Greg Kroah-Hartman',
	'Felipe Balbi', linux-usb, 'Kalle Valo',
	'David S. Miller',
	linux-wireless, netdev, 'Darren Hart',
	'Andy Shevchenko',
	platform-driver-x86, 'Zhang Rui',
	'Rafael J. Wysocki', linux-pm, 'Len Brown',
	linux-acpi, 'Nick Hu', 'Greentime Hu',
	'Vincent Chen', 'Guo Ren',
	linux-csky, 'Tony Luck', 'Fenghua Yu',
	linux-ia64, 'Michal Simek', 'Michael Ellerman',
	'Arnd Bergmann', 'Geoff Levand',
	linuxppc-dev, 'Paul E . McKenney',
	'Jonathan Corbet', 'Randy Dunlap',
	'Davidlohr Bueso'

> -----Original Message-----
> From: Thomas Gleixner <tglx@linutronix.de>
...
> Subject: [patch V3 08/20] hexagon: Remove mm.h from asm/uaccess.h
> 
> From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> 
> The defconfig compiles without linux/mm.h. With mm.h included the include
> chain leands to:
> |   CC      kernel/locking/percpu-rwsem.o
> | In file included from include/linux/huge_mm.h:8,
> |                  from include/linux/mm.h:567,
> |                  from arch/hexagon/include/asm/uaccess.h:,
> |                  from include/linux/uaccess.h:11,
> |                  from include/linux/sched/task.h:11,
> |                  from include/linux/sched/signal.h:9,
> |                  from include/linux/rcuwait.h:6,
> |                  from include/linux/percpu-rwsem.h:8,
> |                  from kernel/locking/percpu-rwsem.c:6:
> | include/linux/fs.h:1422:29: error: array type has incomplete element type
> 'struct percpu_rw_semaphore'
> |  1422 |  struct percpu_rw_semaphore rw_sem[SB_FREEZE_LEVELS];
> 
> once rcuwait.h includes linux/sched/signal.h.
> 
> Remove the linux/mm.h include.
> 
> Reported-by: kbuild test robot <lkp@intel.com>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> Cc: Brian Cain <bcain@codeaurora.org>
> Cc: linux-hexagon@vger.kernel.org
> ---
> V3: New patch
> ---
>  arch/hexagon/include/asm/uaccess.h | 1 -
>  1 file changed, 1 deletion(-)
> 
> diff --git a/arch/hexagon/include/asm/uaccess.h
> b/arch/hexagon/include/asm/uaccess.h
> index 00cb38faad0c4..c1019a736ff13 100644
> --- a/arch/hexagon/include/asm/uaccess.h
> +++ b/arch/hexagon/include/asm/uaccess.h
> @@ -10,7 +10,6 @@
>  /*
>   * User space memory access functions
>   */
> -#include <linux/mm.h>
>  #include <asm/sections.h>
> 
>  /*
> --
> 2.26.0.rc2
> 

Acked-by: Brian Cain <bcain@codeaurora.org>

^ permalink raw reply	[flat|nested] 38+ messages in thread

* Re: [patch V3 13/20] Documentation: Add lock ordering and nesting documentation
  2020-03-23  2:55   ` Paul E. McKenney
@ 2020-03-24 23:13     ` Thomas Gleixner
  2020-03-25  0:28       ` Paul E. McKenney
  0 siblings, 1 reply; 38+ messages in thread
From: Thomas Gleixner @ 2020-03-24 23:13 UTC (permalink / raw)
  To: paulmck
  Cc: LKML, Peter Zijlstra, Ingo Molnar, Sebastian Siewior,
	Linus Torvalds, Joel Fernandes, Oleg Nesterov, Davidlohr Bueso,
	Jonathan Corbet, Randy Dunlap, Logan Gunthorpe, Bjorn Helgaas,
	Kurt Schwemmer, linux-pci, Greg Kroah-Hartman, Felipe Balbi,
	linux-usb, Kalle Valo, David S. Miller, linux-wireless, netdev,
	Darren Hart, Andy Shevchenko, platform-driver-x86, Zhang Rui,
	Rafael J. Wysocki, linux-pm, Len Brown, linux-acpi,
	kbuild test robot, Nick Hu, Greentime Hu, Vincent Chen, Guo Ren,
	linux-csky, Brian Cain, linux-hexagon, Tony Luck, Fenghua Yu,
	linux-ia64, Michal Simek, Michael Ellerman, Arnd Bergmann,
	Geoff Levand, linuxppc-dev, Davidlohr Bueso

Paul,

"Paul E. McKenney" <paulmck@kernel.org> writes:
> On Sat, Mar 21, 2020 at 12:25:57PM +0100, Thomas Gleixner wrote:
> In the normal case where the task sleeps through the entire lock
> acquisition, the sequence of events is as follows:
>
>      state = UNINTERRUPTIBLE
>      lock()
>        block()
>          real_state = state
>          state = SLEEPONLOCK
>
>                                lock wakeup
>                                  state = real_state == UNINTERRUPTIBLE
>
> This sequence of events can occur when the task acquires spinlocks
> on its way to sleeping, for example, in a call to wait_event().
>
> The non-lock wakeup can occur when a wakeup races with this wait_event(),
> which can result in the following sequence of events:
>
>      state = UNINTERRUPTIBLE
>      lock()
>        block()
>          real_state = state
>          state = SLEEPONLOCK
>
>                              non lock wakeup
>                                  real_state = RUNNING
>
>                                lock wakeup
>                                  state = real_state == RUNNING
>
> Without this real_state subterfuge, the wakeup might be lost.

I added this with a few modifications which reflect the actual
implementation. Conceptually the same.

> rwsems have grown special-purpose interfaces that allow non-owner release.
> This non-owner release prevents PREEMPT_RT from substituting RT-mutex
> implementations, for example, by defeating priority inheritance.
> After all, if the lock has no owner, whose priority should be boosted?
> As a result, PREEMPT_RT does not currently support rwsem, which in turn
> means that code using it must therefore be disabled until a workable
> solution presents itself.
>
> [ Note: Not as confident as I would like to be in the above. ]

I'm not confident either especially not after looking at the actual
code.

In fact I feel really stupid because the rw_semaphore reader non-owner
restriction on RT simply does not exist anymore and my history biased
memory tricked me.

The first rw_semaphore implementation of RT was simple and restricted
the reader side to a single reader to support PI on both the reader and
the writer side. That obviosuly did not scale well and made mmap_sem
heavy use cases pretty unhappy.

The short interlude with multi-reader boosting turned out to be a failed
experiment - Steven might still disagree though :)

At some point we gave up and I myself (sic!) reimplemented the RT
variant of rw_semaphore with a reader biased mechanism.

The reader never holds the underlying rt_mutex accross the read side
critical section. It merily increments the reader count and drops it on
release.

The only time a reader takes the rt_mutex is when it blocks on a
writer. Writers hold the rt_mutex across the write side critical section
to allow incoming readers to boost them. Once the writer releases the
rw_semaphore it unlocks the rt_mutex which is then handed off to the
readers. They increment the reader count and then drop the rt_mutex
before continuing in the read side critical section.

So while I changed the implementation it did obviously not occur to me
that this also lifted the non-owner release restriction. Nobody else
noticed either. So we kept dragging this along in both memory and
implementation. Both will be fixed now :)

The owner semantics of down/up_read() are only enforced by lockdep. That
applies to both RT and !RT. The up/down_read_non_owner() variants are
just there to tell lockdep about it.

So, I picked up your other suggestions with slight modifications and
adjusted the owner, semaphore and rw_semaphore docs accordingly.

Please have a close look at the patch below (applies on tip core/locking).

Thanks,

        tglx, who is searching a brown paperbag

8<----------

 Documentation/locking/locktypes.rst |  148 +++++++++++++++++++++++-------------
 1 file changed, 98 insertions(+), 50 deletions(-)

--- a/Documentation/locking/locktypes.rst
+++ b/Documentation/locking/locktypes.rst
@@ -67,6 +67,17 @@ Spinning locks implicitly disable preemp
  _irqsave/restore()   Save and disable / restore interrupt disabled state
  ===================  ====================================================
 
+Owner semantics
+===============
+
+The aforementioned lock types except semaphores have strict owner
+semantics:
+
+  The context (task) that acquired the lock must release it.
+
+rw_semaphores have a special interface which allows non-owner release for
+readers.
+
 
 rtmutex
 =======
@@ -83,6 +94,51 @@ interrupt handlers and soft interrupts.
 and rwlock_t to be implemented via RT-mutexes.
 
 
+sempahore
+=========
+
+semaphore is a counting semaphore implementation.
+
+Semaphores are often used for both serialization and waiting, but new use
+cases should instead use separate serialization and wait mechanisms, such
+as mutexes and completions.
+
+sempahores and PREEMPT_RT
+----------------------------
+
+PREEMPT_RT does not change the sempahore implementation. That's impossible
+due to the counting semaphore semantics which have no concept of owners.
+The lack of an owner conflicts with priority inheritance. After all an
+unknown owner cannot be boosted. As a consequence blocking on semaphores
+can be subject to priority inversion.
+
+
+rw_sempahore
+============
+
+rw_semaphore is a multiple readers and single writer lock mechanism.
+
+On non-PREEMPT_RT kernels the implementation is fair, thus preventing
+writer starvation.
+
+rw_semaphore complies by default with the strict owner semantics, but there
+exist special-purpose interfaces that allow non-owner release for readers.
+These work independent of the kernel configuration.
+
+rw_sempahore and PREEMPT_RT
+---------------------------
+
+PREEMPT_RT kernels map rw_sempahore to a separate rt_mutex-based
+implementation, thus changing the fairness:
+
+ Because an rw_sempaphore writer cannot grant its priority to multiple
+ readers, a preempted low-priority reader will continue holding its lock,
+ thus starving even high-priority writers.  In contrast, because readers
+ can grant their priority to a writer, a preempted low-priority writer will
+ have its priority boosted until it releases the lock, thus preventing that
+ writer from starving readers.
+
+
 raw_spinlock_t and spinlock_t
 =============================
 
@@ -140,7 +196,16 @@ On a PREEMPT_RT enabled kernel spinlock_
    kernels leave task state untouched.  However, PREEMPT_RT must change
    task state if the task blocks during acquisition.  Therefore, it saves
    the current task state before blocking and the corresponding lock wakeup
-   restores it.
+   restores it::
+
+    task->state = TASK_INTERRUPTIBLE
+     lock()
+       block()
+         task->saved_state = task->state
+	 task->state = TASK_UNINTERRUPTIBLE
+	 schedule()
+					lock wakeup
+					  task->state = task->saved_state
 
    Other types of wakeups would normally unconditionally set the task state
    to RUNNING, but that does not work here because the task must remain
@@ -148,7 +213,22 @@ On a PREEMPT_RT enabled kernel spinlock_
    wakeup attempts to awaken a task blocked waiting for a spinlock, it
    instead sets the saved state to RUNNING.  Then, when the lock
    acquisition completes, the lock wakeup sets the task state to the saved
-   state, in this case setting it to RUNNING.
+   state, in this case setting it to RUNNING::
+
+    task->state = TASK_INTERRUPTIBLE
+     lock()
+       block()
+         task->saved_state = task->state
+	 task->state = TASK_UNINTERRUPTIBLE
+	 schedule()
+					non lock wakeup
+					  task->saved_state = TASK_RUNNING
+
+					lock wakeup
+					  task->state = task->saved_state
+
+   This ensures that the real wakeup cannot be lost.
+
 
 rwlock_t
 ========
@@ -228,17 +308,16 @@ while holding normal non-raw spinlocks b
 bit spinlocks
 -------------
 
-Bit spinlocks are problematic for PREEMPT_RT as they cannot be easily
-substituted by an RT-mutex based implementation for obvious reasons.
-
-The semantics of bit spinlocks are preserved on PREEMPT_RT kernels and the
-caveats vs. raw_spinlock_t apply.
-
-Some bit spinlocks are substituted by regular spinlock_t for PREEMPT_RT but
-this requires conditional (#ifdef'ed) code changes at the usage site while
-the spinlock_t substitution is simply done by the compiler and the
-conditionals are restricted to header files and core implementation of the
-locking primitives and the usage sites do not require any changes.
+PREEMPT_RT cannot substitute bit spinlocks because a single bit is too
+small to accommodate an RT-mutex.  Therefore, the semantics of bit
+spinlocks are preserved on PREEMPT_RT kernels, so that the raw_spinlock_t
+caveats also apply to bit spinlocks.
+
+Some bit spinlocks are replaced with regular spinlock_t for PREEMPT_RT
+using conditional (#ifdef'ed) code changes at the usage site.  In contrast,
+usage-site changes are not needed for the spinlock_t substitution.
+Instead, conditionals in header files and the core locking implemementation
+enable the compiler to do the substitution transparently.
 
 
 Lock type nesting rules
@@ -254,46 +333,15 @@ Lock type nesting rules
 
   - Spinning lock types can nest inside sleeping lock types.
 
-These rules apply in general independent of CONFIG_PREEMPT_RT.
+These constraints apply both in CONFIG_PREEMPT_RT and otherwise.
 
-As PREEMPT_RT changes the lock category of spinlock_t and rwlock_t from
-spinning to sleeping this has obviously restrictions how they can nest with
-raw_spinlock_t.
-
-This results in the following nest ordering:
+The fact that PREEMPT_RT changes the lock category of spinlock_t and
+rwlock_t from spinning to sleeping means that they cannot be acquired while
+holding a raw spinlock.  This results in the following nesting ordering:
 
   1) Sleeping locks
   2) spinlock_t and rwlock_t
   3) raw_spinlock_t and bit spinlocks
 
-Lockdep is aware of these constraints to ensure that they are respected.
-
-
-Owner semantics
-===============
-
-Most lock types in the Linux kernel have strict owner semantics, i.e. the
-context (task) which acquires a lock has to release it.
-
-There are two exceptions:
-
-  - semaphores
-  - rwsems
-
-semaphores have no owner semantics for historical reason, and as such
-trylock and release operations can be called from any context. They are
-often used for both serialization and waiting purposes. That's generally
-discouraged and should be replaced by separate serialization and wait
-mechanisms, such as mutexes and completions.
-
-rwsems have grown interfaces which allow non owner release for special
-purposes. This usage is problematic on PREEMPT_RT because PREEMPT_RT
-substitutes all locking primitives except semaphores with RT-mutex based
-implementations to provide priority inheritance for all lock types except
-the truly spinning ones. Priority inheritance on ownerless locks is
-obviously impossible.
-
-For now the rwsem non-owner release excludes code which utilizes it from
-being used on PREEMPT_RT enabled kernels. In same cases this can be
-mitigated by disabling portions of the code, in other cases the complete
-functionality has to be disabled until a workable solution has been found.
+Lockdep will complain if these constraints are violated, both in
+CONFIG_PREEMPT_RT and otherwise.


^ permalink raw reply	[flat|nested] 38+ messages in thread

* Re: [patch V3 13/20] Documentation: Add lock ordering and nesting documentation
  2020-03-24 23:13     ` Thomas Gleixner
@ 2020-03-25  0:28       ` Paul E. McKenney
  2020-03-25 12:27         ` Documentation/locking/locktypes: Further clarifications and wordsmithing Thomas Gleixner
  0 siblings, 1 reply; 38+ messages in thread
From: Paul E. McKenney @ 2020-03-25  0:28 UTC (permalink / raw)
  To: Thomas Gleixner
  Cc: LKML, Peter Zijlstra, Ingo Molnar, Sebastian Siewior,
	Linus Torvalds, Joel Fernandes, Oleg Nesterov, Davidlohr Bueso,
	Jonathan Corbet, Randy Dunlap, Logan Gunthorpe, Bjorn Helgaas,
	Kurt Schwemmer, linux-pci, Greg Kroah-Hartman, Felipe Balbi,
	linux-usb, Kalle Valo, David S. Miller, linux-wireless, netdev,
	Darren Hart, Andy Shevchenko, platform-driver-x86, Zhang Rui,
	Rafael J. Wysocki, linux-pm, Len Brown, linux-acpi,
	kbuild test robot, Nick Hu, Greentime Hu, Vincent Chen, Guo Ren,
	linux-csky, Brian Cain, linux-hexagon, Tony Luck, Fenghua Yu,
	linux-ia64, Michal Simek, Michael Ellerman, Arnd Bergmann,
	Geoff Levand, linuxppc-dev, Davidlohr Bueso

On Wed, Mar 25, 2020 at 12:13:34AM +0100, Thomas Gleixner wrote:
> Paul,
> 
> "Paul E. McKenney" <paulmck@kernel.org> writes:
> > On Sat, Mar 21, 2020 at 12:25:57PM +0100, Thomas Gleixner wrote:
> > In the normal case where the task sleeps through the entire lock
> > acquisition, the sequence of events is as follows:
> >
> >      state = UNINTERRUPTIBLE
> >      lock()
> >        block()
> >          real_state = state
> >          state = SLEEPONLOCK
> >
> >                                lock wakeup
> >                                  state = real_state == UNINTERRUPTIBLE
> >
> > This sequence of events can occur when the task acquires spinlocks
> > on its way to sleeping, for example, in a call to wait_event().
> >
> > The non-lock wakeup can occur when a wakeup races with this wait_event(),
> > which can result in the following sequence of events:
> >
> >      state = UNINTERRUPTIBLE
> >      lock()
> >        block()
> >          real_state = state
> >          state = SLEEPONLOCK
> >
> >                              non lock wakeup
> >                                  real_state = RUNNING
> >
> >                                lock wakeup
> >                                  state = real_state == RUNNING
> >
> > Without this real_state subterfuge, the wakeup might be lost.
> 
> I added this with a few modifications which reflect the actual
> implementation. Conceptually the same.

Looks good!

> > rwsems have grown special-purpose interfaces that allow non-owner release.
> > This non-owner release prevents PREEMPT_RT from substituting RT-mutex
> > implementations, for example, by defeating priority inheritance.
> > After all, if the lock has no owner, whose priority should be boosted?
> > As a result, PREEMPT_RT does not currently support rwsem, which in turn
> > means that code using it must therefore be disabled until a workable
> > solution presents itself.
> >
> > [ Note: Not as confident as I would like to be in the above. ]
> 
> I'm not confident either especially not after looking at the actual
> code.
> 
> In fact I feel really stupid because the rw_semaphore reader non-owner
> restriction on RT simply does not exist anymore and my history biased
> memory tricked me.

I guess I am glad that it is not just me.  ;-)

> The first rw_semaphore implementation of RT was simple and restricted
> the reader side to a single reader to support PI on both the reader and
> the writer side. That obviosuly did not scale well and made mmap_sem
> heavy use cases pretty unhappy.
> 
> The short interlude with multi-reader boosting turned out to be a failed
> experiment - Steven might still disagree though :)
> 
> At some point we gave up and I myself (sic!) reimplemented the RT
> variant of rw_semaphore with a reader biased mechanism.
> 
> The reader never holds the underlying rt_mutex accross the read side
> critical section. It merily increments the reader count and drops it on
> release.
> 
> The only time a reader takes the rt_mutex is when it blocks on a
> writer. Writers hold the rt_mutex across the write side critical section
> to allow incoming readers to boost them. Once the writer releases the
> rw_semaphore it unlocks the rt_mutex which is then handed off to the
> readers. They increment the reader count and then drop the rt_mutex
> before continuing in the read side critical section.
> 
> So while I changed the implementation it did obviously not occur to me
> that this also lifted the non-owner release restriction. Nobody else
> noticed either. So we kept dragging this along in both memory and
> implementation. Both will be fixed now :)
> 
> The owner semantics of down/up_read() are only enforced by lockdep. That
> applies to both RT and !RT. The up/down_read_non_owner() variants are
> just there to tell lockdep about it.
> 
> So, I picked up your other suggestions with slight modifications and
> adjusted the owner, semaphore and rw_semaphore docs accordingly.
> 
> Please have a close look at the patch below (applies on tip core/locking).
> 
> Thanks,
> 
>         tglx, who is searching a brown paperbag

Sorry, used all the ones here over the past few days.  :-/

Please see below for a wordsmithing patch to be applied on top of
or merged into the patch in your email.

							Thanx, Paul

------------------------------------------------------------------------

commit e38c64ce8db45e2b0a19082f1e1f988c3b25fb81
Author: Paul E. McKenney <paulmck@kernel.org>
Date:   Tue Mar 24 17:23:36 2020 -0700

    Documentation: Wordsmith lock ordering and nesting documentation
    
    This commit is strictly wordsmithing with no (intended) semantic
    changes.
    
    Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

diff --git a/Documentation/locking/locktypes.rst b/Documentation/locking/locktypes.rst
index ca7bf84..8eb52e9 100644
--- a/Documentation/locking/locktypes.rst
+++ b/Documentation/locking/locktypes.rst
@@ -94,7 +94,7 @@ interrupt handlers and soft interrupts.  This conversion allows spinlock_t
 and rwlock_t to be implemented via RT-mutexes.
 
 
-sempahore
+semaphore
 =========
 
 semaphore is a counting semaphore implementation.
@@ -103,17 +103,17 @@ Semaphores are often used for both serialization and waiting, but new use
 cases should instead use separate serialization and wait mechanisms, such
 as mutexes and completions.
 
-sempahores and PREEMPT_RT
+semaphores and PREEMPT_RT
 ----------------------------
 
-PREEMPT_RT does not change the sempahore implementation. That's impossible
-due to the counting semaphore semantics which have no concept of owners.
-The lack of an owner conflicts with priority inheritance. After all an
-unknown owner cannot be boosted. As a consequence blocking on semaphores
-can be subject to priority inversion.
+PREEMPT_RT does not change the semaphore implementation because counting
+semaphores have no concept of owners, thus preventing PREEMPT_RT from
+providing priority inheritance for semaphores.  After all, an unknown
+owner cannot be boosted. As a consequence, blocking on semaphores can
+result in priority inversion.
 
 
-rw_sempahore
+rw_semaphore
 ============
 
 rw_semaphore is a multiple readers and single writer lock mechanism.
@@ -125,13 +125,13 @@ rw_semaphore complies by default with the strict owner semantics, but there
 exist special-purpose interfaces that allow non-owner release for readers.
 These work independent of the kernel configuration.
 
-rw_sempahore and PREEMPT_RT
+rw_semaphore and PREEMPT_RT
 ---------------------------
 
-PREEMPT_RT kernels map rw_sempahore to a separate rt_mutex-based
+PREEMPT_RT kernels map rw_semaphore to a separate rt_mutex-based
 implementation, thus changing the fairness:
 
- Because an rw_sempaphore writer cannot grant its priority to multiple
+ Because an rw_semaphore writer cannot grant its priority to multiple
  readers, a preempted low-priority reader will continue holding its lock,
  thus starving even high-priority writers.  In contrast, because readers
  can grant their priority to a writer, a preempted low-priority writer will
@@ -158,7 +158,7 @@ critical section is tiny, thus avoiding RT-mutex overhead.
 spinlock_t
 ----------
 
-The semantics of spinlock_t change with the state of CONFIG_PREEMPT_RT.
+The semantics of spinlock_t change with the state of PREEMPT_RT.
 
 On a non PREEMPT_RT enabled kernel spinlock_t is mapped to raw_spinlock_t
 and has exactly the same semantics.
@@ -196,7 +196,7 @@ PREEMPT_RT kernels preserve all other spinlock_t semantics:
    kernels leave task state untouched.  However, PREEMPT_RT must change
    task state if the task blocks during acquisition.  Therefore, it saves
    the current task state before blocking and the corresponding lock wakeup
-   restores it::
+   restores it, as shown below::
 
     task->state = TASK_INTERRUPTIBLE
      lock()
@@ -333,7 +333,7 @@ The most basic rules are:
 
   - Spinning lock types can nest inside sleeping lock types.
 
-These constraints apply both in CONFIG_PREEMPT_RT and otherwise.
+These constraints apply both in PREEMPT_RT and otherwise.
 
 The fact that PREEMPT_RT changes the lock category of spinlock_t and
 rwlock_t from spinning to sleeping means that they cannot be acquired while
@@ -344,4 +344,4 @@ holding a raw spinlock.  This results in the following nesting ordering:
   3) raw_spinlock_t and bit spinlocks
 
 Lockdep will complain if these constraints are violated, both in
-CONFIG_PREEMPT_RT and otherwise.
+PREEMPT_RT and otherwise.

^ permalink raw reply	[flat|nested] 38+ messages in thread

* Re: [patch V3 03/20] usb: gadget: Use completion interface instead of open coding it
  2020-03-21 11:25 ` [patch V3 03/20] usb: gadget: Use completion interface instead of open coding it Thomas Gleixner
@ 2020-03-25  8:37   ` Felipe Balbi
  2020-03-27 12:14     ` Sebastian Siewior
  0 siblings, 1 reply; 38+ messages in thread
From: Felipe Balbi @ 2020-03-25  8:37 UTC (permalink / raw)
  To: Thomas Gleixner, LKML
  Cc: Peter Zijlstra, Ingo Molnar, Sebastian Siewior, Linus Torvalds,
	Joel Fernandes, Oleg Nesterov, Davidlohr Bueso,
	Greg Kroah-Hartman, linux-usb, Logan Gunthorpe, Bjorn Helgaas,
	Kurt Schwemmer, linux-pci, Kalle Valo, David S. Miller,
	linux-wireless, netdev, Darren Hart, Andy Shevchenko,
	platform-driver-x86, Zhang Rui, Rafael J. Wysocki, linux-pm,
	Len Brown, linux-acpi, kbuild test robot, Nick Hu, Greentime Hu,
	Vincent Chen, Guo Ren, linux-csky, Brian Cain, linux-hexagon,
	Tony Luck, Fenghua Yu, linux-ia64, Michal Simek,
	Michael Ellerman, Arnd Bergmann, Geoff Levand, linuxppc-dev,
	Paul E . McKenney, Jonathan Corbet, Randy Dunlap,
	Davidlohr Bueso

[-- Attachment #1: Type: text/plain, Size: 1032 bytes --]

Thomas Gleixner <tglx@linutronix.de> writes:

> From: Thomas Gleixner <tglx@linutronix.de>
>
> ep_io() uses a completion on stack and open codes the waiting with:
>
>   wait_event_interruptible (done.wait, done.done);
> and
>   wait_event (done.wait, done.done);
>
> This waits in non-exclusive mode for complete(), but there is no reason to
> do so because the completion can only be waited for by the task itself and
> complete() wakes exactly one exlusive waiter.
>
> Replace the open coded implementation with the corresponding
> wait_for_completion*() functions.
>
> No functional change.
>
> Reported-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Cc: Felipe Balbi <balbi@kernel.org>
> Cc: linux-usb@vger.kernel.org

Do you want to carry it via your tree? If so:

Acked-by: Felipe Balbi <balbi@kernel.org>

Otherwise, let me know and I'll pick this patch.

-- 
balbi

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 832 bytes --]

^ permalink raw reply	[flat|nested] 38+ messages in thread

* Documentation/locking/locktypes: Further clarifications and wordsmithing
  2020-03-25  0:28       ` Paul E. McKenney
@ 2020-03-25 12:27         ` Thomas Gleixner
  2020-03-25 16:02           ` Sebastian Siewior
  2020-03-25 16:58           ` [PATCH v2] Documentation/locking/locktypes: minor copy editor fixes Randy Dunlap
  0 siblings, 2 replies; 38+ messages in thread
From: Thomas Gleixner @ 2020-03-25 12:27 UTC (permalink / raw)
  To: paulmck
  Cc: LKML, Peter Zijlstra, Ingo Molnar, Sebastian Siewior,
	Linus Torvalds, Joel Fernandes, Oleg Nesterov, Davidlohr Bueso,
	Jonathan Corbet, Randy Dunlap, Logan Gunthorpe, Bjorn Helgaas,
	Kurt Schwemmer, linux-pci, Greg Kroah-Hartman, Felipe Balbi,
	linux-usb, Kalle Valo, David S. Miller, linux-wireless, netdev,
	Darren Hart, Andy Shevchenko, platform-driver-x86, Zhang Rui,
	Rafael J. Wysocki, linux-pm, Len Brown, linux-acpi,
	kbuild test robot, Nick Hu, Greentime Hu, Vincent Chen, Guo Ren,
	linux-csky, Brian Cain, linux-hexagon, Tony Luck, Fenghua Yu,
	linux-ia64, Michal Simek, Michael Ellerman, Arnd Bergmann,
	Geoff Levand, linuxppc-dev, Davidlohr Bueso

The documentation of rw_semaphores is wrong as it claims that the non-owner
reader release is not supported by RT. That's just history biased memory
distortion.

Split the 'Owner semantics' section up and add separate sections for
semaphore and rw_semaphore to reflect reality.

Aside of that the following updates are done:

 - Add pseudo code to document the spinlock state preserving mechanism on
   PREEMPT_RT

 - Wordsmith the bitspinlock and lock nesting sections

Co-developed-by: Paul McKenney <paulmck@kernel.org>
Signed-off-by: Paul McKenney <paulmck@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
 Documentation/locking/locktypes.rst |  150 +++++++++++++++++++++++-------------
 1 file changed, 99 insertions(+), 51 deletions(-)

--- a/Documentation/locking/locktypes.rst
+++ b/Documentation/locking/locktypes.rst
@@ -67,6 +67,17 @@ Spinning locks implicitly disable preemp
  _irqsave/restore()   Save and disable / restore interrupt disabled state
  ===================  ====================================================
 
+Owner semantics
+===============
+
+The aforementioned lock types except semaphores have strict owner
+semantics:
+
+  The context (task) that acquired the lock must release it.
+
+rw_semaphores have a special interface which allows non-owner release for
+readers.
+
 
 rtmutex
 =======
@@ -83,6 +94,51 @@ interrupt handlers and soft interrupts.
 and rwlock_t to be implemented via RT-mutexes.
 
 
+semaphore
+=========
+
+semaphore is a counting semaphore implementation.
+
+Semaphores are often used for both serialization and waiting, but new use
+cases should instead use separate serialization and wait mechanisms, such
+as mutexes and completions.
+
+semaphores and PREEMPT_RT
+----------------------------
+
+PREEMPT_RT does not change the semaphore implementation because counting
+semaphores have no concept of owners, thus preventing PREEMPT_RT from
+providing priority inheritance for semaphores.  After all, an unknown
+owner cannot be boosted. As a consequence, blocking on semaphores can
+result in priority inversion.
+
+
+rw_semaphore
+============
+
+rw_semaphore is a multiple readers and single writer lock mechanism.
+
+On non-PREEMPT_RT kernels the implementation is fair, thus preventing
+writer starvation.
+
+rw_semaphore complies by default with the strict owner semantics, but there
+exist special-purpose interfaces that allow non-owner release for readers.
+These work independent of the kernel configuration.
+
+rw_semaphore and PREEMPT_RT
+---------------------------
+
+PREEMPT_RT kernels map rw_semaphore to a separate rt_mutex-based
+implementation, thus changing the fairness:
+
+ Because an rw_semaphore writer cannot grant its priority to multiple
+ readers, a preempted low-priority reader will continue holding its lock,
+ thus starving even high-priority writers.  In contrast, because readers
+ can grant their priority to a writer, a preempted low-priority writer will
+ have its priority boosted until it releases the lock, thus preventing that
+ writer from starving readers.
+
+
 raw_spinlock_t and spinlock_t
 =============================
 
@@ -102,7 +158,7 @@ critical section is tiny, thus avoiding
 spinlock_t
 ----------
 
-The semantics of spinlock_t change with the state of CONFIG_PREEMPT_RT.
+The semantics of spinlock_t change with the state of PREEMPT_RT.
 
 On a non PREEMPT_RT enabled kernel spinlock_t is mapped to raw_spinlock_t
 and has exactly the same semantics.
@@ -140,7 +196,16 @@ On a PREEMPT_RT enabled kernel spinlock_
    kernels leave task state untouched.  However, PREEMPT_RT must change
    task state if the task blocks during acquisition.  Therefore, it saves
    the current task state before blocking and the corresponding lock wakeup
-   restores it.
+   restores it, as shown below::
+
+    task->state = TASK_INTERRUPTIBLE
+     lock()
+       block()
+         task->saved_state = task->state
+	 task->state = TASK_UNINTERRUPTIBLE
+	 schedule()
+					lock wakeup
+					  task->state = task->saved_state
 
    Other types of wakeups would normally unconditionally set the task state
    to RUNNING, but that does not work here because the task must remain
@@ -148,7 +213,22 @@ On a PREEMPT_RT enabled kernel spinlock_
    wakeup attempts to awaken a task blocked waiting for a spinlock, it
    instead sets the saved state to RUNNING.  Then, when the lock
    acquisition completes, the lock wakeup sets the task state to the saved
-   state, in this case setting it to RUNNING.
+   state, in this case setting it to RUNNING::
+
+    task->state = TASK_INTERRUPTIBLE
+     lock()
+       block()
+         task->saved_state = task->state
+	 task->state = TASK_UNINTERRUPTIBLE
+	 schedule()
+					non lock wakeup
+					  task->saved_state = TASK_RUNNING
+
+					lock wakeup
+					  task->state = task->saved_state
+
+   This ensures that the real wakeup cannot be lost.
+
 
 rwlock_t
 ========
@@ -228,17 +308,16 @@ while holding normal non-raw spinlocks b
 bit spinlocks
 -------------
 
-Bit spinlocks are problematic for PREEMPT_RT as they cannot be easily
-substituted by an RT-mutex based implementation for obvious reasons.
-
-The semantics of bit spinlocks are preserved on PREEMPT_RT kernels and the
-caveats vs. raw_spinlock_t apply.
-
-Some bit spinlocks are substituted by regular spinlock_t for PREEMPT_RT but
-this requires conditional (#ifdef'ed) code changes at the usage site while
-the spinlock_t substitution is simply done by the compiler and the
-conditionals are restricted to header files and core implementation of the
-locking primitives and the usage sites do not require any changes.
+PREEMPT_RT cannot substitute bit spinlocks because a single bit is too
+small to accommodate an RT-mutex.  Therefore, the semantics of bit
+spinlocks are preserved on PREEMPT_RT kernels, so that the raw_spinlock_t
+caveats also apply to bit spinlocks.
+
+Some bit spinlocks are replaced with regular spinlock_t for PREEMPT_RT
+using conditional (#ifdef'ed) code changes at the usage site.  In contrast,
+usage-site changes are not needed for the spinlock_t substitution.
+Instead, conditionals in header files and the core locking implemementation
+enable the compiler to do the substitution transparently.
 
 
 Lock type nesting rules
@@ -254,46 +333,15 @@ Lock type nesting rules
 
   - Spinning lock types can nest inside sleeping lock types.
 
-These rules apply in general independent of CONFIG_PREEMPT_RT.
+These constraints apply both in PREEMPT_RT and otherwise.
 
-As PREEMPT_RT changes the lock category of spinlock_t and rwlock_t from
-spinning to sleeping this has obviously restrictions how they can nest with
-raw_spinlock_t.
-
-This results in the following nest ordering:
+The fact that PREEMPT_RT changes the lock category of spinlock_t and
+rwlock_t from spinning to sleeping means that they cannot be acquired while
+holding a raw spinlock.  This results in the following nesting ordering:
 
   1) Sleeping locks
   2) spinlock_t and rwlock_t
   3) raw_spinlock_t and bit spinlocks
 
-Lockdep is aware of these constraints to ensure that they are respected.
-
-
-Owner semantics
-===============
-
-Most lock types in the Linux kernel have strict owner semantics, i.e. the
-context (task) which acquires a lock has to release it.
-
-There are two exceptions:
-
-  - semaphores
-  - rwsems
-
-semaphores have no owner semantics for historical reason, and as such
-trylock and release operations can be called from any context. They are
-often used for both serialization and waiting purposes. That's generally
-discouraged and should be replaced by separate serialization and wait
-mechanisms, such as mutexes and completions.
-
-rwsems have grown interfaces which allow non owner release for special
-purposes. This usage is problematic on PREEMPT_RT because PREEMPT_RT
-substitutes all locking primitives except semaphores with RT-mutex based
-implementations to provide priority inheritance for all lock types except
-the truly spinning ones. Priority inheritance on ownerless locks is
-obviously impossible.
-
-For now the rwsem non-owner release excludes code which utilizes it from
-being used on PREEMPT_RT enabled kernels. In same cases this can be
-mitigated by disabling portions of the code, in other cases the complete
-functionality has to be disabled until a workable solution has been found.
+Lockdep will complain if these constraints are violated, both in
+PREEMPT_RT and otherwise.

^ permalink raw reply	[flat|nested] 38+ messages in thread

* Re: Documentation/locking/locktypes: Further clarifications and wordsmithing
  2020-03-25 12:27         ` Documentation/locking/locktypes: Further clarifications and wordsmithing Thomas Gleixner
@ 2020-03-25 16:02           ` Sebastian Siewior
  2020-03-25 16:39             ` Paul E. McKenney
  2020-03-25 16:58           ` [PATCH v2] Documentation/locking/locktypes: minor copy editor fixes Randy Dunlap
  1 sibling, 1 reply; 38+ messages in thread
From: Sebastian Siewior @ 2020-03-25 16:02 UTC (permalink / raw)
  To: Thomas Gleixner
  Cc: paulmck, LKML, Peter Zijlstra, Ingo Molnar, Linus Torvalds,
	Joel Fernandes, Oleg Nesterov, Davidlohr Bueso, Jonathan Corbet,
	Randy Dunlap, Logan Gunthorpe, Bjorn Helgaas, Kurt Schwemmer,
	linux-pci, Greg Kroah-Hartman, Felipe Balbi, linux-usb,
	Kalle Valo, David S. Miller, linux-wireless, netdev, Darren Hart,
	Andy Shevchenko, platform-driver-x86, Zhang Rui,
	Rafael J. Wysocki, linux-pm, Len Brown, linux-acpi,
	kbuild test robot, Nick Hu, Greentime Hu, Vincent Chen, Guo Ren,
	linux-csky, Brian Cain, linux-hexagon, Tony Luck, Fenghua Yu,
	linux-ia64, Michal Simek, Michael Ellerman, Arnd Bergmann,
	Geoff Levand, linuxppc-dev, Davidlohr Bueso

On 2020-03-25 13:27:49 [+0100], Thomas Gleixner wrote:
> The documentation of rw_semaphores is wrong as it claims that the non-owner
> reader release is not supported by RT. That's just history biased memory
> distortion.
> 
> Split the 'Owner semantics' section up and add separate sections for
> semaphore and rw_semaphore to reflect reality.
> 
> Aside of that the following updates are done:
> 
>  - Add pseudo code to document the spinlock state preserving mechanism on
>    PREEMPT_RT
> 
>  - Wordsmith the bitspinlock and lock nesting sections
> 
> Co-developed-by: Paul McKenney <paulmck@kernel.org>
> Signed-off-by: Paul McKenney <paulmck@kernel.org>
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

> --- a/Documentation/locking/locktypes.rst
> +++ b/Documentation/locking/locktypes.rst
> +rw_semaphore
> +============
> +
> +rw_semaphore is a multiple readers and single writer lock mechanism.
> +
> +On non-PREEMPT_RT kernels the implementation is fair, thus preventing
> +writer starvation.
> +
> +rw_semaphore complies by default with the strict owner semantics, but there
> +exist special-purpose interfaces that allow non-owner release for readers.
> +These work independent of the kernel configuration.

This reads funny, could be my English. "This works independent …" maybe?

Sebastian

^ permalink raw reply	[flat|nested] 38+ messages in thread

* Re: Documentation/locking/locktypes: Further clarifications and wordsmithing
  2020-03-25 16:02           ` Sebastian Siewior
@ 2020-03-25 16:39             ` Paul E. McKenney
  2020-03-25 16:54               ` Sebastian Siewior
  0 siblings, 1 reply; 38+ messages in thread
From: Paul E. McKenney @ 2020-03-25 16:39 UTC (permalink / raw)
  To: Sebastian Siewior
  Cc: Thomas Gleixner, LKML, Peter Zijlstra, Ingo Molnar,
	Linus Torvalds, Joel Fernandes, Oleg Nesterov, Davidlohr Bueso,
	Jonathan Corbet, Randy Dunlap, Logan Gunthorpe, Bjorn Helgaas,
	Kurt Schwemmer, linux-pci, Greg Kroah-Hartman, Felipe Balbi,
	linux-usb, Kalle Valo, David S. Miller, linux-wireless, netdev,
	Darren Hart, Andy Shevchenko, platform-driver-x86, Zhang Rui,
	Rafael J. Wysocki, linux-pm, Len Brown, linux-acpi,
	kbuild test robot, Nick Hu, Greentime Hu, Vincent Chen, Guo Ren,
	linux-csky, Brian Cain, linux-hexagon, Tony Luck, Fenghua Yu,
	linux-ia64, Michal Simek, Michael Ellerman, Arnd Bergmann,
	Geoff Levand, linuxppc-dev, Davidlohr Bueso

On Wed, Mar 25, 2020 at 05:02:12PM +0100, Sebastian Siewior wrote:
> On 2020-03-25 13:27:49 [+0100], Thomas Gleixner wrote:
> > The documentation of rw_semaphores is wrong as it claims that the non-owner
> > reader release is not supported by RT. That's just history biased memory
> > distortion.
> > 
> > Split the 'Owner semantics' section up and add separate sections for
> > semaphore and rw_semaphore to reflect reality.
> > 
> > Aside of that the following updates are done:
> > 
> >  - Add pseudo code to document the spinlock state preserving mechanism on
> >    PREEMPT_RT
> > 
> >  - Wordsmith the bitspinlock and lock nesting sections
> > 
> > Co-developed-by: Paul McKenney <paulmck@kernel.org>
> > Signed-off-by: Paul McKenney <paulmck@kernel.org>
> > Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> Acked-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> 
> > --- a/Documentation/locking/locktypes.rst
> > +++ b/Documentation/locking/locktypes.rst
> …
> > +rw_semaphore
> > +============
> > +
> > +rw_semaphore is a multiple readers and single writer lock mechanism.
> > +
> > +On non-PREEMPT_RT kernels the implementation is fair, thus preventing
> > +writer starvation.
> > +
> > +rw_semaphore complies by default with the strict owner semantics, but there
> > +exist special-purpose interfaces that allow non-owner release for readers.
> > +These work independent of the kernel configuration.
> 
> This reads funny, could be my English. "This works independent …" maybe?

The "These" refers to "interfaces", which is plural, so "These" rather
than "This".  But yes, it is a bit awkward, because you have to skip
back past "readers", "release", and "non-owner" to find the implied
subject of that last sentence.

So how about this instead, making the implied subject explicit?

rw_semaphore complies by default with the strict owner semantics, but there
exist special-purpose interfaces that allow non-owner release for readers.
These interfaces work independent of the kernel configuration.

							Thanx, Paul

^ permalink raw reply	[flat|nested] 38+ messages in thread

* Re: Documentation/locking/locktypes: Further clarifications and wordsmithing
  2020-03-25 16:39             ` Paul E. McKenney
@ 2020-03-25 16:54               ` Sebastian Siewior
  0 siblings, 0 replies; 38+ messages in thread
From: Sebastian Siewior @ 2020-03-25 16:54 UTC (permalink / raw)
  To: Paul E. McKenney
  Cc: Thomas Gleixner, LKML, Peter Zijlstra, Ingo Molnar,
	Linus Torvalds, Joel Fernandes, Oleg Nesterov, Davidlohr Bueso,
	Jonathan Corbet, Randy Dunlap, Logan Gunthorpe, Bjorn Helgaas,
	Kurt Schwemmer, linux-pci, Greg Kroah-Hartman, Felipe Balbi,
	linux-usb, Kalle Valo, David S. Miller, linux-wireless, netdev,
	Darren Hart, Andy Shevchenko, platform-driver-x86, Zhang Rui,
	Rafael J. Wysocki, linux-pm, Len Brown, linux-acpi,
	kbuild test robot, Nick Hu, Greentime Hu, Vincent Chen, Guo Ren,
	linux-csky, Brian Cain, linux-hexagon, Tony Luck, Fenghua Yu,
	linux-ia64, Michal Simek, Michael Ellerman, Arnd Bergmann,
	Geoff Levand, linuxppc-dev, Davidlohr Bueso

On 2020-03-25 09:39:19 [-0700], Paul E. McKenney wrote:
> > > --- a/Documentation/locking/locktypes.rst
> > > +++ b/Documentation/locking/locktypes.rst
> > …
> > > +rw_semaphore
> > > +============
> > > +
> > > +rw_semaphore is a multiple readers and single writer lock mechanism.
> > > +
> > > +On non-PREEMPT_RT kernels the implementation is fair, thus preventing
> > > +writer starvation.
> > > +
> > > +rw_semaphore complies by default with the strict owner semantics, but there
> > > +exist special-purpose interfaces that allow non-owner release for readers.
> > > +These work independent of the kernel configuration.
> > 
> > This reads funny, could be my English. "This works independent …" maybe?
> 
> The "These" refers to "interfaces", which is plural, so "These" rather
> than "This".  But yes, it is a bit awkward, because you have to skip
> back past "readers", "release", and "non-owner" to find the implied
> subject of that last sentence.
> 
> So how about this instead, making the implied subject explicit?
> 
> rw_semaphore complies by default with the strict owner semantics, but there
> exist special-purpose interfaces that allow non-owner release for readers.
> These interfaces work independent of the kernel configuration.

Yes, perfect. Thank you.

> 							Thanx, Paul

Sebastian

^ permalink raw reply	[flat|nested] 38+ messages in thread

* [PATCH v2] Documentation/locking/locktypes: minor copy editor fixes
  2020-03-25 12:27         ` Documentation/locking/locktypes: Further clarifications and wordsmithing Thomas Gleixner
  2020-03-25 16:02           ` Sebastian Siewior
@ 2020-03-25 16:58           ` Randy Dunlap
  2020-03-26  2:40             ` Paul E. McKenney
  1 sibling, 1 reply; 38+ messages in thread
From: Randy Dunlap @ 2020-03-25 16:58 UTC (permalink / raw)
  To: Thomas Gleixner, paulmck
  Cc: LKML, Peter Zijlstra, Ingo Molnar, Sebastian Siewior,
	Linus Torvalds, Joel Fernandes, Oleg Nesterov, Davidlohr Bueso,
	Jonathan Corbet, Logan Gunthorpe, Bjorn Helgaas, Kurt Schwemmer,
	linux-pci, Greg Kroah-Hartman, Felipe Balbi, linux-usb,
	Kalle Valo, David S. Miller, linux-wireless, netdev, Darren Hart,
	Andy Shevchenko, platform-driver-x86, Zhang Rui,
	Rafael J. Wysocki, linux-pm, Len Brown, linux-acpi,
	kbuild test robot, Nick Hu, Greentime Hu, Vincent Chen, Guo Ren,
	linux-csky, Brian Cain, linux-hexagon, Tony Luck, Fenghua Yu,
	linux-ia64, Michal Simek, Michael Ellerman, Arnd Bergmann,
	Geoff Levand, linuxppc-dev, Davidlohr Bueso

From: Randy Dunlap <rdunlap@infradead.org>

Minor editorial fixes:
- add some hyphens in multi-word adjectives
- add some periods for consistency
- add "'" for possessive CPU's
- capitalize IRQ when it's an acronym and not part of a function name

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Paul McKenney <paulmck@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Sebastian Siewior <bigeasy@linutronix.de>
Cc: Joel Fernandes <joel@joelfernandes.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
---
 Documentation/locking/locktypes.rst |   16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

--- linux-next-20200325.orig/Documentation/locking/locktypes.rst
+++ linux-next-20200325/Documentation/locking/locktypes.rst
@@ -84,7 +84,7 @@ rtmutex
 
 RT-mutexes are mutexes with support for priority inheritance (PI).
 
-PI has limitations on non PREEMPT_RT enabled kernels due to preemption and
+PI has limitations on non-PREEMPT_RT-enabled kernels due to preemption and
 interrupt disabled sections.
 
 PI clearly cannot preempt preemption-disabled or interrupt-disabled
@@ -150,7 +150,7 @@ kernel configuration including PREEMPT_R
 
 raw_spinlock_t is a strict spinning lock implementation in all kernels,
 including PREEMPT_RT kernels.  Use raw_spinlock_t only in real critical
-core code, low level interrupt handling and places where disabling
+core code, low-level interrupt handling and places where disabling
 preemption or interrupts is required, for example, to safely access
 hardware state.  raw_spinlock_t can sometimes also be used when the
 critical section is tiny, thus avoiding RT-mutex overhead.
@@ -160,20 +160,20 @@ spinlock_t
 
 The semantics of spinlock_t change with the state of PREEMPT_RT.
 
-On a non PREEMPT_RT enabled kernel spinlock_t is mapped to raw_spinlock_t
+On a non-PREEMPT_RT-enabled kernel spinlock_t is mapped to raw_spinlock_t
 and has exactly the same semantics.
 
 spinlock_t and PREEMPT_RT
 -------------------------
 
-On a PREEMPT_RT enabled kernel spinlock_t is mapped to a separate
+On a PREEMPT_RT-enabled kernel spinlock_t is mapped to a separate
 implementation based on rt_mutex which changes the semantics:
 
- - Preemption is not disabled
+ - Preemption is not disabled.
 
  - The hard interrupt related suffixes for spin_lock / spin_unlock
-   operations (_irq, _irqsave / _irqrestore) do not affect the CPUs
-   interrupt disabled state
+   operations (_irq, _irqsave / _irqrestore) do not affect the CPU's
+   interrupt disabled state.
 
  - The soft interrupt related suffix (_bh()) still disables softirq
    handlers.
@@ -279,7 +279,7 @@ fully preemptible context.  Instead, use
 spin_lock_irqsave() and their unlock counterparts.  In cases where the
 interrupt disabling and locking must remain separate, PREEMPT_RT offers a
 local_lock mechanism.  Acquiring the local_lock pins the task to a CPU,
-allowing things like per-CPU irq-disabled locks to be acquired.  However,
+allowing things like per-CPU IRQ-disabled locks to be acquired.  However,
 this approach should be used only where absolutely necessary.
 
 


^ permalink raw reply	[flat|nested] 38+ messages in thread

* Re: [PATCH v2] Documentation/locking/locktypes: minor copy editor fixes
  2020-03-25 16:58           ` [PATCH v2] Documentation/locking/locktypes: minor copy editor fixes Randy Dunlap
@ 2020-03-26  2:40             ` Paul E. McKenney
  0 siblings, 0 replies; 38+ messages in thread
From: Paul E. McKenney @ 2020-03-26  2:40 UTC (permalink / raw)
  To: Randy Dunlap
  Cc: Thomas Gleixner, LKML, Peter Zijlstra, Ingo Molnar,
	Sebastian Siewior, Linus Torvalds, Joel Fernandes, Oleg Nesterov,
	Davidlohr Bueso, Jonathan Corbet, Logan Gunthorpe, Bjorn Helgaas,
	Kurt Schwemmer, linux-pci, Greg Kroah-Hartman, Felipe Balbi,
	linux-usb, Kalle Valo, David S. Miller, linux-wireless, netdev,
	Darren Hart, Andy Shevchenko, platform-driver-x86, Zhang Rui,
	Rafael J. Wysocki, linux-pm, Len Brown, linux-acpi,
	kbuild test robot, Nick Hu, Greentime Hu, Vincent Chen, Guo Ren,
	linux-csky, Brian Cain, linux-hexagon, Tony Luck, Fenghua Yu,
	linux-ia64, Michal Simek, Michael Ellerman, Arnd Bergmann,
	Geoff Levand, linuxppc-dev, Davidlohr Bueso

On Wed, Mar 25, 2020 at 09:58:14AM -0700, Randy Dunlap wrote:
> From: Randy Dunlap <rdunlap@infradead.org>
> 
> Minor editorial fixes:
> - add some hyphens in multi-word adjectives
> - add some periods for consistency
> - add "'" for possessive CPU's
> - capitalize IRQ when it's an acronym and not part of a function name
> 
> Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
> Cc: Paul McKenney <paulmck@kernel.org>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Sebastian Siewior <bigeasy@linutronix.de>
> Cc: Joel Fernandes <joel@joelfernandes.org>
> Cc: Ingo Molnar <mingo@kernel.org>
> Cc: Peter Zijlstra <peterz@infradead.org>

Some nits below, but with or without those suggested changes:

Reviewed-by: Paul E. McKenney <paulmck@kernel.org>

> ---
>  Documentation/locking/locktypes.rst |   16 ++++++++--------
>  1 file changed, 8 insertions(+), 8 deletions(-)
> 
> --- linux-next-20200325.orig/Documentation/locking/locktypes.rst
> +++ linux-next-20200325/Documentation/locking/locktypes.rst
> @@ -84,7 +84,7 @@ rtmutex
>  
>  RT-mutexes are mutexes with support for priority inheritance (PI).
>  
> -PI has limitations on non PREEMPT_RT enabled kernels due to preemption and
> +PI has limitations on non-PREEMPT_RT-enabled kernels due to preemption and

Or just drop the " enabled".

>  interrupt disabled sections.
>  
>  PI clearly cannot preempt preemption-disabled or interrupt-disabled
> @@ -150,7 +150,7 @@ kernel configuration including PREEMPT_R
>  
>  raw_spinlock_t is a strict spinning lock implementation in all kernels,
>  including PREEMPT_RT kernels.  Use raw_spinlock_t only in real critical
> -core code, low level interrupt handling and places where disabling
> +core code, low-level interrupt handling and places where disabling
>  preemption or interrupts is required, for example, to safely access
>  hardware state.  raw_spinlock_t can sometimes also be used when the
>  critical section is tiny, thus avoiding RT-mutex overhead.
> @@ -160,20 +160,20 @@ spinlock_t
>  
>  The semantics of spinlock_t change with the state of PREEMPT_RT.
>  
> -On a non PREEMPT_RT enabled kernel spinlock_t is mapped to raw_spinlock_t
> +On a non-PREEMPT_RT-enabled kernel spinlock_t is mapped to raw_spinlock_t

Ditto.

>  and has exactly the same semantics.
>  
>  spinlock_t and PREEMPT_RT
>  -------------------------
>  
> -On a PREEMPT_RT enabled kernel spinlock_t is mapped to a separate
> +On a PREEMPT_RT-enabled kernel spinlock_t is mapped to a separate

And here as well.

>  implementation based on rt_mutex which changes the semantics:
>  
> - - Preemption is not disabled
> + - Preemption is not disabled.
>  
>   - The hard interrupt related suffixes for spin_lock / spin_unlock
> -   operations (_irq, _irqsave / _irqrestore) do not affect the CPUs
> -   interrupt disabled state
> +   operations (_irq, _irqsave / _irqrestore) do not affect the CPU's
> +   interrupt disabled state.
>  
>   - The soft interrupt related suffix (_bh()) still disables softirq
>     handlers.
> @@ -279,7 +279,7 @@ fully preemptible context.  Instead, use
>  spin_lock_irqsave() and their unlock counterparts.  In cases where the
>  interrupt disabling and locking must remain separate, PREEMPT_RT offers a
>  local_lock mechanism.  Acquiring the local_lock pins the task to a CPU,
> -allowing things like per-CPU irq-disabled locks to be acquired.  However,
> +allowing things like per-CPU IRQ-disabled locks to be acquired.  However,

Quite a bit of text in the kernel uses "irq", lower case.  Another
option is to spell out "interrupt".

>  this approach should be used only where absolutely necessary.
>  
>  
> 

^ permalink raw reply	[flat|nested] 38+ messages in thread

* Re: [patch V3 03/20] usb: gadget: Use completion interface instead of open coding it
  2020-03-25  8:37   ` Felipe Balbi
@ 2020-03-27 12:14     ` Sebastian Siewior
  0 siblings, 0 replies; 38+ messages in thread
From: Sebastian Siewior @ 2020-03-27 12:14 UTC (permalink / raw)
  To: Felipe Balbi
  Cc: Thomas Gleixner, LKML, Peter Zijlstra, Ingo Molnar,
	Linus Torvalds, Joel Fernandes, Oleg Nesterov, Davidlohr Bueso,
	Greg Kroah-Hartman, linux-usb, Logan Gunthorpe, Bjorn Helgaas,
	Kurt Schwemmer, linux-pci, Kalle Valo, David S. Miller,
	linux-wireless, netdev, Darren Hart, Andy Shevchenko,
	platform-driver-x86, Zhang Rui, Rafael J. Wysocki, linux-pm,
	Len Brown, linux-acpi, kbuild test robot, Nick Hu, Greentime Hu,
	Vincent Chen, Guo Ren, linux-csky, Brian Cain, linux-hexagon,
	Tony Luck, Fenghua Yu, linux-ia64, Michal Simek,
	Michael Ellerman, Arnd Bergmann, Geoff Levand, linuxppc-dev,
	Paul E . McKenney, Jonathan Corbet, Randy Dunlap,
	Davidlohr Bueso

On 2020-03-25 10:37:57 [+0200], Felipe Balbi wrote:
> Do you want to carry it via your tree? If so:

We would like to do so.

> Acked-by: Felipe Balbi <balbi@kernel.org>

Thank you.

> Otherwise, let me know and I'll pick this patch.

Sebastian

^ permalink raw reply	[flat|nested] 38+ messages in thread

* Re: [patch V3 12/20] powerpc/ps3: Convert half completion to rcuwait
  2020-03-21 11:25 ` [patch V3 12/20] powerpc/ps3: Convert half completion to rcuwait Thomas Gleixner
  2020-03-21 13:22   ` Thomas Gleixner
@ 2020-03-27 19:14   ` Geoff Levand
  1 sibling, 0 replies; 38+ messages in thread
From: Geoff Levand @ 2020-03-27 19:14 UTC (permalink / raw)
  To: Thomas Gleixner, LKML
  Cc: Peter Zijlstra, Ingo Molnar, Sebastian Siewior, Linus Torvalds,
	Joel Fernandes, Oleg Nesterov, Davidlohr Bueso, Michael Ellerman,
	Arnd Bergmann, linuxppc-dev, Logan Gunthorpe, Bjorn Helgaas,
	Kurt Schwemmer, linux-pci, Greg Kroah-Hartman, Felipe Balbi,
	linux-usb, Kalle Valo, David S. Miller, linux-wireless, netdev,
	Darren Hart, Andy Shevchenko, platform-driver-x86, Zhang Rui,
	Rafael J. Wysocki, linux-pm, Len Brown, linux-acpi,
	kbuild test robot, Nick Hu, Greentime Hu, Vincent Chen, Guo Ren,
	linux-csky, Brian Cain, linux-hexagon, Tony Luck, Fenghua Yu,
	linux-ia64, Michal Simek, Paul E . McKenney, Jonathan Corbet,
	Randy Dunlap, Davidlohr Bueso

Hi,

On 3/21/20 4:25 AM, Thomas Gleixner wrote:
> From: Thomas Gleixner <tglx@linutronix.de>
> 
> The PS3 notification interrupt and kthread use a hacked up completion to
> communicate. Since we're wanting to change the completion implementation and
> this is abuse anyway, replace it with a simple rcuwait since there is only ever
> the one waiter.
> 
> AFAICT the kthread uses TASK_INTERRUPTIBLE to not increase loadavg, kthreads
> cannot receive signals by default and this one doesn't look different. Use
> TASK_IDLE instead.

I tested the patch set applied against v5.6-rc7 on the PS3 and it worked
as expected.

Tested by: Geoff Levand <geoff@infradead.org>


^ permalink raw reply	[flat|nested] 38+ messages in thread

end of thread, back to index

Thread overview: 38+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2020-03-21 11:25 [patch V3 00/20] Lock ordering documentation and annotation for lockdep Thomas Gleixner
2020-03-21 11:25 ` [patch V3 01/20] PCI/switchtec: Fix init_completion race condition with poll_wait() Thomas Gleixner
2020-03-21 11:25 ` [patch V3 02/20] pci/switchtec: Replace completion wait queue usage for poll Thomas Gleixner
2020-03-21 11:25 ` [patch V3 03/20] usb: gadget: Use completion interface instead of open coding it Thomas Gleixner
2020-03-25  8:37   ` Felipe Balbi
2020-03-27 12:14     ` Sebastian Siewior
2020-03-21 11:25 ` [patch V3 04/20] orinoco_usb: Use the regular completion interfaces Thomas Gleixner
2020-03-21 11:25 ` [patch V3 05/20] acpi: Remove header dependency Thomas Gleixner
2020-03-21 11:25 ` [patch V3 06/20] nds32: Remove mm.h from asm/uaccess.h Thomas Gleixner
2020-03-21 11:25 ` [patch V3 07/20] csky: " Thomas Gleixner
2020-03-21 11:25 ` [patch V3 08/20] hexagon: " Thomas Gleixner
2020-03-23 21:46   ` Brian Cain
2020-03-21 11:25 ` [patch V3 09/20] ia64: " Thomas Gleixner
2020-03-21 11:25 ` [patch V3 10/20] microblaze: " Thomas Gleixner
2020-03-21 11:25 ` [patch V3 11/20] rcuwait: Add @state argument to rcuwait_wait_event() Thomas Gleixner
2020-03-21 11:25 ` [patch V3 12/20] powerpc/ps3: Convert half completion to rcuwait Thomas Gleixner
2020-03-21 13:22   ` Thomas Gleixner
2020-03-27 19:14   ` Geoff Levand
2020-03-21 11:25 ` [patch V3 13/20] Documentation: Add lock ordering and nesting documentation Thomas Gleixner
2020-03-23  2:55   ` Paul E. McKenney
2020-03-24 23:13     ` Thomas Gleixner
2020-03-25  0:28       ` Paul E. McKenney
2020-03-25 12:27         ` Documentation/locking/locktypes: Further clarifications and wordsmithing Thomas Gleixner
2020-03-25 16:02           ` Sebastian Siewior
2020-03-25 16:39             ` Paul E. McKenney
2020-03-25 16:54               ` Sebastian Siewior
2020-03-25 16:58           ` [PATCH v2] Documentation/locking/locktypes: minor copy editor fixes Randy Dunlap
2020-03-26  2:40             ` Paul E. McKenney
2020-03-21 11:25 ` [patch V3 14/20] timekeeping: Split jiffies seqlock Thomas Gleixner
2020-03-21 11:25 ` [patch V3 15/20] sched/swait: Prepare usage in completions Thomas Gleixner
2020-03-21 11:26 ` [patch V3 16/20] completion: Use simple wait queues Thomas Gleixner
2020-03-23 15:20   ` [PATCH] completion: Use lockdep_assert_RT_in_threaded_ctx() in complete_all() Sebastian Siewior
2020-03-21 11:26 ` [patch V3 17/20] lockdep: Introduce wait-type checks Thomas Gleixner
2020-03-21 11:26 ` [patch V3 18/20] lockdep: Add hrtimer context tracing bits Thomas Gleixner
2020-03-21 11:26 ` [patch V3 19/20] lockdep: Annotate irq_work Thomas Gleixner
2020-03-21 11:26 ` [patch V3 20/20] lockdep: Add posixtimer context tracing bits Thomas Gleixner
2020-03-21 17:19 ` [patch V3 00/20] Lock ordering documentation and annotation for lockdep Davidlohr Bueso
2020-03-21 17:45   ` Thomas Gleixner

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