From: Thomas Gleixner <tglx@linutronix.de>
To: LKML <linux-kernel@vger.kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
Ingo Molnar <mingo@kernel.org>, Will Deacon <will@kernel.org>,
"Paul E . McKenney" <paulmck@kernel.org>,
Joel Fernandes <joel@joelfernandes.org>,
Steven Rostedt <rostedt@goodmis.org>,
Randy Dunlap <rdunlap@infradead.org>,
Arnd Bergmann <arnd@arndb.de>,
Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
Logan Gunthorpe <logang@deltatee.com>,
Kurt Schwemmer <kurt.schwemmer@microsemi.com>,
Bjorn Helgaas <bhelgaas@google.com>,
linux-pci@vger.kernel.org, Felipe Balbi <balbi@kernel.org>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
linux-usb@vger.kernel.org, Kalle Valo <kvalo@codeaurora.org>,
"David S. Miller" <davem@davemloft.net>,
linux-wireless@vger.kernel.org, netdev@vger.kernel.org,
Oleg Nesterov <oleg@redhat.com>,
Davidlohr Bueso <dave@stgolabs.net>,
Michael Ellerman <mpe@ellerman.id.au>,
linuxppc-dev@lists.ozlabs.org
Subject: [patch V2 11/15] completion: Use simple wait queues
Date: Wed, 18 Mar 2020 21:43:13 +0100 [thread overview]
Message-ID: <20200318204408.521507446@linutronix.de> (raw)
In-Reply-To: 20200318204302.693307984@linutronix.de
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>
Cc: Arnd Bergmann <arnd@arndb.de>
---
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);
next prev parent reply other threads:[~2020-03-18 20:48 UTC|newest]
Thread overview: 72+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-18 20:43 [patch V2 00/15] Lock ordering documentation and annotation for lockdep Thomas Gleixner
2020-03-18 20:43 ` [patch V2 01/15] PCI/switchtec: Fix init_completion race condition with poll_wait() Thomas Gleixner
2020-03-18 21:25 ` Bjorn Helgaas
2020-03-18 20:43 ` [patch V2 02/15] pci/switchtec: Replace completion wait queue usage for poll Thomas Gleixner
2020-03-18 21:26 ` Bjorn Helgaas
2020-03-18 22:11 ` Logan Gunthorpe
2020-03-18 20:43 ` [patch V2 03/15] usb: gadget: Use completion interface instead of open coding it Thomas Gleixner
2020-03-19 8:41 ` Greg Kroah-Hartman
2020-03-18 20:43 ` [patch V2 04/15] orinoco_usb: Use the regular completion interfaces Thomas Gleixner
2020-03-19 8:40 ` Greg Kroah-Hartman
2020-03-18 20:43 ` [patch V2 05/15] acpi: Remove header dependency Thomas Gleixner
2020-03-18 20:43 ` [patch V2 06/15] rcuwait: Add @state argument to rcuwait_wait_event() Thomas Gleixner
2020-03-20 5:36 ` Davidlohr Bueso
2020-03-20 8:45 ` Sebastian Andrzej Siewior
2020-03-20 8:58 ` Davidlohr Bueso
2020-03-20 9:48 ` [PATCH 0/5] Remove mm.h from arch/*/include/asm/uaccess.h Sebastian Andrzej Siewior
2020-03-20 9:48 ` [PATCH 1/5] nds32: Remove mm.h from asm/uaccess.h Sebastian Andrzej Siewior
2020-03-20 9:48 ` [PATCH 2/5] csky: " Sebastian Andrzej Siewior
2020-03-21 11:24 ` Guo Ren
2020-03-21 12:08 ` Thomas Gleixner
2020-03-21 14:11 ` Guo Ren
2020-03-20 9:48 ` [PATCH 3/5] hexagon: " Sebastian Andrzej Siewior
2020-03-20 9:48 ` [PATCH 4/5] ia64: " Sebastian Andrzej Siewior
2020-03-20 9:48 ` [PATCH 5/5] microblaze: " Sebastian Andrzej Siewior
2020-03-18 20:43 ` [patch V2 07/15] powerpc/ps3: Convert half completion to rcuwait Thomas Gleixner
2020-03-19 9:00 ` Sebastian Andrzej Siewior
2020-03-19 9:18 ` Peter Zijlstra
2020-03-19 9:21 ` Davidlohr Bueso
2020-03-19 10:04 ` Christoph Hellwig
2020-03-19 10:26 ` Sebastian Andrzej Siewior
2020-03-20 0:01 ` Geoff Levand
2020-03-20 0:45 ` Michael Ellerman
2020-03-21 10:41 ` Thomas Gleixner
2020-03-18 20:43 ` [patch V2 08/15] Documentation: Add lock ordering and nesting documentation Thomas Gleixner
2020-03-18 22:31 ` Paul E. McKenney
2020-03-19 18:02 ` Thomas Gleixner
2020-03-20 16:01 ` Paul E. McKenney
2020-03-20 19:51 ` Thomas Gleixner
2020-03-20 21:02 ` Paul E. McKenney
2020-03-20 22:36 ` Thomas Gleixner
2020-03-21 2:29 ` Paul E. McKenney
2020-03-21 10:26 ` Thomas Gleixner
2020-03-21 17:23 ` Paul E. McKenney
2020-03-19 8:51 ` Davidlohr Bueso
2020-03-19 15:04 ` Jonathan Corbet
2020-03-19 18:04 ` Thomas Gleixner
2020-03-21 21:21 ` Joel Fernandes
2020-03-21 21:49 ` Thomas Gleixner
2020-03-22 1:36 ` Joel Fernandes
2020-03-18 20:43 ` [patch V2 09/15] timekeeping: Split jiffies seqlock Thomas Gleixner
2020-03-18 20:43 ` [patch V2 10/15] sched/swait: Prepare usage in completions Thomas Gleixner
2020-03-18 20:43 ` Thomas Gleixner [this message]
2020-03-18 22:28 ` [patch V2 11/15] completion: Use simple wait queues Logan Gunthorpe
2020-03-19 0:33 ` Joel Fernandes
2020-03-19 0:44 ` Thomas Gleixner
2020-03-19 8:42 ` Greg Kroah-Hartman
2020-03-19 17:12 ` Linus Torvalds
2020-03-19 23:25 ` Julian Calaby
2020-03-20 6:59 ` Christoph Hellwig
2020-03-20 9:01 ` Davidlohr Bueso
2020-03-20 8:50 ` [patch V2 00/15] Lock ordering documentation and annotation for lockdep Davidlohr Bueso
2020-03-20 8:55 ` [PATCH 16/15] rcuwait: Get rid of stale name comment Davidlohr Bueso
2020-03-20 8:55 ` [PATCH 17/15] rcuwait: Inform rcuwait_wake_up() users if a wakeup was attempted Davidlohr Bueso
2020-03-20 9:13 ` Sebastian Andrzej Siewior
2020-03-20 10:44 ` Peter Zijlstra
2020-03-20 8:55 ` [PATCH 18/15] kvm: Replace vcpu->swait with rcuwait Davidlohr Bueso
2020-03-20 11:20 ` Paolo Bonzini
2020-03-20 12:54 ` Peter Zijlstra
2020-03-22 16:33 ` Davidlohr Bueso
2020-03-22 22:32 ` Peter Zijlstra
2020-03-20 8:55 ` [PATCH 19/15] sched/swait: Reword some of the main description Davidlohr Bueso
2020-03-20 9:19 ` Sebastian Andrzej Siewior
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