[PATCH V3 00/11] The panic notifiers refactor - fixes/clean-ups (V3)

[PATCH V3 00/11] The panic notifiers refactor - fixes/clean-ups (V3)

[Guilherme G. Piccoli]

Hey everybody, this the third iteration of the panic notifiers
fixes/clean-ups;

V2 available at:
https://lore.kernel.org/lkml/20220719195325.402745-1-gpiccoli@igalia.com/

V1 (including the refactor) available at:
https://lore.kernel.org/lkml/20220427224924.592546-1-gpiccoli@igalia.com/


There wasn't much change here compared to V2 (the specifics are in the
patches), but a global change is that I've rebased against 6.0-rc1.
One patch got merged in -next, another one was re-submit in a standalone
format (requested by maintainer), so both of these are not here anymore.


As usual, tested this series building for all affected architecture/drivers
and also through some boot/runtime tests; below the test "matrix" used:

Build tests (using cross-compilers): alpha, arm, arm64, parisc, um, x86_64.
Boot/Runtime tests: x86_64 (QEMU guests and Steam Deck).

Here is the link with the .config files used:
https://people.igalia.com/gpiccoli/panic_notifiers_configs/6.0-rc1/


About the merge strategy: I've noticed there is a difference in maintainers
preferences (and my preference as well), so I see 3 strategies for merge:

(a) Maintainers pick patches that are good from the series and merge in
their trees;

(b) Some maintainer would pick the whole series and merge, at once, given
that everything is fine/ack/reviewed.

(c) I must re-send patches individually once they are reviewed/acked, as
standalone patches to the relevant maintainers, so they can merge it in
their trees.

I'm willing to do what's best for everybody - (a) is my choice when possible,
(b) seems to stall things and potentially cause conflicts, (c) seems to be
the compromise. I'll do that as per preference of the respective maintainers.


As usual, reviews / comments are always welcome, thanks in advance for them!
Cheers,

Guilherme


Guilherme G. Piccoli (11):
  ARM: Disable FIQs (but not IRQs) on CPUs shutdown paths
  notifier: Add panic notifiers info and purge trailing whitespaces
  alpha: Clean-up the panic notifier code
  um: Improve panic notifiers consistency and ordering
  parisc: Replace regular spinlock with spin_trylock on panic path
  tracing: Improve panic/die notifiers
  notifiers: Add tracepoints to the notifiers infrastructure
  EDAC/altera: Skip the panic notifier if kdump is loaded
  video/hyperv_fb: Avoid taking busy spinlock on panic path
  drivers/hv/vmbus, video/hyperv_fb: Untangle and refactor Hyper-V panic notifiers
  panic: Fixes the panic_print NMI backtrace setting

 arch/alpha/kernel/setup.c        |  36 +++++-----
 arch/arm/kernel/machine_kexec.c  |   2 +
 arch/arm/kernel/smp.c            |   5 +-
 arch/parisc/include/asm/pdc.h    |   1 +
 arch/parisc/kernel/firmware.c    |  27 ++++++--
 arch/um/drivers/mconsole_kern.c  |   7 +-
 arch/um/kernel/um_arch.c         |   8 +--
 drivers/edac/altera_edac.c       |  16 +++--
 drivers/hv/ring_buffer.c         |  13 ++++
 drivers/hv/vmbus_drv.c           | 109 +++++++++++++++++++------------
 drivers/parisc/power.c           |  17 +++--
 drivers/video/fbdev/hyperv_fb.c  |  16 ++++-
 include/linux/hyperv.h           |   2 +
 include/linux/notifier.h         |   8 ++-
 include/trace/events/notifiers.h |  69 +++++++++++++++++++
 kernel/notifier.c                |   6 ++
 kernel/panic.c                   |  47 +++++++------
 kernel/trace/trace.c             |  55 ++++++++--------
 18 files changed, 302 insertions(+), 142 deletions(-)
 create mode 100644 include/trace/events/notifiers.h

-- 
2.37.2

[PATCH V3 05/11] parisc: Replace regular spinlock with spin_trylock on panic path

[Guilherme G. Piccoli]

The panic notifiers' callbacks execute in an atomic context, with
interrupts/preemption disabled, and all CPUs not running the panic
function are off, so it's very dangerous to wait on a regular
spinlock, there's a risk of deadlock.

Refactor the panic notifier of parisc/power driver to make use
of spin_trylock - for that, we've added a second version of the
soft-power function. Also, some comments were reorganized and
trailing white spaces, useless header inclusion and blank lines
were removed.

Cc: "James E.J. Bottomley" <James.Bottomley@HansenPartnership.com>
Cc: Jeroen Roovers <jer@xs4all.nl>
Acked-by: Helge Deller <deller@gmx.de> # parisc
Signed-off-by: Guilherme G. Piccoli <gpiccoli@igalia.com>

---

V3:
- s/in/on as per Jeroen's suggestion - thanks!

V2:
- Added Helge's ACK - thanks!


 arch/parisc/include/asm/pdc.h |  1 +
 arch/parisc/kernel/firmware.c | 27 +++++++++++++++++++++++----
 drivers/parisc/power.c        | 17 ++++++++++-------
 3 files changed, 34 insertions(+), 11 deletions(-)

diff --git a/arch/parisc/include/asm/pdc.h b/arch/parisc/include/asm/pdc.h
index b643092d4b98..7a106008e258 100644
--- a/arch/parisc/include/asm/pdc.h
+++ b/arch/parisc/include/asm/pdc.h
@@ -83,6 +83,7 @@ int pdc_do_firm_test_reset(unsigned long ftc_bitmap);
 int pdc_do_reset(void);
 int pdc_soft_power_info(unsigned long *power_reg);
 int pdc_soft_power_button(int sw_control);
+int pdc_soft_power_button_panic(int sw_control);
 void pdc_io_reset(void);
 void pdc_io_reset_devices(void);
 int pdc_iodc_getc(void);
diff --git a/arch/parisc/kernel/firmware.c b/arch/parisc/kernel/firmware.c
index 6a7e315bcc2e..3b1f7641e3c9 100644
--- a/arch/parisc/kernel/firmware.c
+++ b/arch/parisc/kernel/firmware.c
@@ -1232,15 +1232,18 @@ int __init pdc_soft_power_info(unsigned long *power_reg)
 }
 
 /*
- * pdc_soft_power_button - Control the soft power button behaviour
- * @sw_control: 0 for hardware control, 1 for software control 
+ * pdc_soft_power_button{_panic} - Control the soft power button behaviour
+ * @sw_control: 0 for hardware control, 1 for software control
  *
  *
  * This PDC function places the soft power button under software or
  * hardware control.
- * Under software control the OS may control to when to allow to shut 
- * down the system. Under hardware control pressing the power button 
+ * Under software control the OS may control to when to allow to shut
+ * down the system. Under hardware control pressing the power button
  * powers off the system immediately.
+ *
+ * The _panic version relies on spin_trylock to prevent deadlock
+ * on panic path.
  */
 int pdc_soft_power_button(int sw_control)
 {
@@ -1254,6 +1257,22 @@ int pdc_soft_power_button(int sw_control)
 	return retval;
 }
 
+int pdc_soft_power_button_panic(int sw_control)
+{
+	int retval;
+	unsigned long flags;
+
+	if (!spin_trylock_irqsave(&pdc_lock, flags)) {
+		pr_emerg("Couldn't enable soft power button\n");
+		return -EBUSY; /* ignored by the panic notifier */
+	}
+
+	retval = mem_pdc_call(PDC_SOFT_POWER, PDC_SOFT_POWER_ENABLE, __pa(pdc_result), sw_control);
+	spin_unlock_irqrestore(&pdc_lock, flags);
+
+	return retval;
+}
+
 /*
  * pdc_io_reset - Hack to avoid overlapping range registers of Bridges devices.
  * Primarily a problem on T600 (which parisc-linux doesn't support) but
diff --git a/drivers/parisc/power.c b/drivers/parisc/power.c
index 456776bd8ee6..8512884de2cf 100644
--- a/drivers/parisc/power.c
+++ b/drivers/parisc/power.c
@@ -37,7 +37,6 @@
 #include <linux/module.h>
 #include <linux/init.h>
 #include <linux/kernel.h>
-#include <linux/notifier.h>
 #include <linux/panic_notifier.h>
 #include <linux/reboot.h>
 #include <linux/sched/signal.h>
@@ -175,16 +174,21 @@ static void powerfail_interrupt(int code, void *x)
 
 
 
-/* parisc_panic_event() is called by the panic handler.
- * As soon as a panic occurs, our tasklets above will not be
- * executed any longer. This function then re-enables the 
- * soft-power switch and allows the user to switch off the system
+/*
+ * parisc_panic_event() is called by the panic handler.
+ *
+ * As soon as a panic occurs, our tasklets above will not
+ * be executed any longer. This function then re-enables
+ * the soft-power switch and allows the user to switch off
+ * the system. We rely in pdc_soft_power_button_panic()
+ * since this version spin_trylocks (instead of regular
+ * spinlock), preventing deadlocks on panic path.
  */
 static int parisc_panic_event(struct notifier_block *this,
 		unsigned long event, void *ptr)
 {
 	/* re-enable the soft-power switch */
-	pdc_soft_power_button(0);
+	pdc_soft_power_button_panic(0);
 	return NOTIFY_DONE;
 }
 
@@ -193,7 +197,6 @@ static struct notifier_block parisc_panic_block = {
 	.priority	= INT_MAX,
 };
 
-
 static int __init power_init(void)
 {
 	unsigned long ret;
-- 
2.37.2