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sched/wake_q: Add helper to call wake_up_q after unlock with preemption disabled

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A common pattern seen when wake_qs are used to defer a wakeup
until after a lock is released is something like:
  preempt_disable();
  raw_spin_unlock(lock);
  wake_up_q(wake_q);
  preempt_enable();

So create some raw_spin_unlock*_wake() helper functions to clean
this up.

Applies on top of the fix I submitted here:
 https://lore.kernel.org/lkml/20241212222138.2400498-1-jstultz@google.com/

NOTE: I recognise the unlock()/unlock_irq()/unlock_irqrestore()
variants creates its own duplication, which we could use a macro
to generate the similar functions, but I often dislike how those
generation macros making finding the actual implementation
harder, so I left the three functions as is. If folks would
prefer otherwise, let me know and I'll switch it.

Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: John Stultz <jstultz@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20241217040803.243420-1-jstultz@google.com
This commit is contained in:
John Stultz 2024-12-16 20:07:35 -08:00 committed by Peter Zijlstra
parent c2db11a750
commit abfdccd6af
4 changed files with 44 additions and 43 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

34
include/linux/sched/wake_q.h
View File

@ -63,4 +63,38 @@ extern void wake_q_add(struct wake_q_head *head, struct task_struct *task);
extern void wake_q_add_safe(struct wake_q_head *head, struct task_struct *task);
extern void wake_up_q(struct wake_q_head *head);
/* Spin unlock helpers to unlock and call wake_up_q with preempt disabled */
static inline
void raw_spin_unlock_wake(raw_spinlock_t *lock, struct wake_q_head *wake_q)
{
guard(preempt)();
raw_spin_unlock(lock);
if (wake_q) {
wake_up_q(wake_q);
wake_q_init(wake_q);
}
}
static inline
void raw_spin_unlock_irq_wake(raw_spinlock_t *lock, struct wake_q_head *wake_q)
{
guard(preempt)();
raw_spin_unlock_irq(lock);
if (wake_q) {
wake_up_q(wake_q);
wake_q_init(wake_q);
}
}
static inline
void raw_spin_unlock_irqrestore_wake(raw_spinlock_t *lock, unsigned long flags,
struct wake_q_head *wake_q)
{
guard(preempt)();
raw_spin_unlock_irqrestore(lock, flags);
if (wake_q) {
wake_up_q(wake_q);
wake_q_init(wake_q);
}
}
#endif /* _LINUX_SCHED_WAKE_Q_H */

5
kernel/futex/pi.c
View File

@ -1020,10 +1020,7 @@ retry_private:
* it sees the futex_q::pi_state.
*/
ret = __rt_mutex_start_proxy_lock(&q.pi_state->pi_mutex, &rt_waiter, current, &wake_q);
preempt_disable();
raw_spin_unlock_irq(&q.pi_state->pi_mutex.wait_lock);
wake_up_q(&wake_q);
preempt_enable();
raw_spin_unlock_irq_wake(&q.pi_state->pi_mutex.wait_lock, &wake_q);
if (ret) {
if (ret == 1)

16
kernel/locking/mutex.c
View File

@ -657,10 +657,7 @@ __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclas
goto err;
}
raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
/* Make sure we do wakeups before calling schedule */
wake_up_q(&wake_q);
wake_q_init(&wake_q);
raw_spin_unlock_irqrestore_wake(&lock->wait_lock, flags, &wake_q);
schedule_preempt_disabled();
@ -710,8 +707,7 @@ skip_wait:
if (ww_ctx)
ww_mutex_lock_acquired(ww, ww_ctx);
raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
wake_up_q(&wake_q);
raw_spin_unlock_irqrestore_wake(&lock->wait_lock, flags, &wake_q);
preempt_enable();
return 0;
@ -720,10 +716,9 @@ err:
__mutex_remove_waiter(lock, &waiter);
err_early_kill:
trace_contention_end(lock, ret);
raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
raw_spin_unlock_irqrestore_wake(&lock->wait_lock, flags, &wake_q);
debug_mutex_free_waiter(&waiter);
mutex_release(&lock->dep_map, ip);
wake_up_q(&wake_q);
preempt_enable();
return ret;
}
@ -935,10 +930,7 @@ static noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigne
if (owner & MUTEX_FLAG_HANDOFF)
__mutex_handoff(lock, next);
preempt_disable();
raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
wake_up_q(&wake_q);
preempt_enable();
raw_spin_unlock_irqrestore_wake(&lock->wait_lock, flags, &wake_q);
}
#ifndef CONFIG_DEBUG_LOCK_ALLOC

32
kernel/locking/rtmutex.c
View File

@ -1292,13 +1292,7 @@ static int __sched task_blocks_on_rt_mutex(struct rt_mutex_base *lock,
*/
get_task_struct(owner);
preempt_disable();
raw_spin_unlock_irq(&lock->wait_lock);
/* wake up any tasks on the wake_q before calling rt_mutex_adjust_prio_chain */
wake_up_q(wake_q);
wake_q_init(wake_q);
preempt_enable();
raw_spin_unlock_irq_wake(&lock->wait_lock, wake_q);
res = rt_mutex_adjust_prio_chain(owner, chwalk, lock,
next_lock, waiter, task);
@ -1642,13 +1636,7 @@ static int __sched rt_mutex_slowlock_block(struct rt_mutex_base *lock,
owner = rt_mutex_owner(lock);
else
owner = NULL;
preempt_disable();
raw_spin_unlock_irq(&lock->wait_lock);
if (wake_q) {
wake_up_q(wake_q);
wake_q_init(wake_q);
}
preempt_enable();
raw_spin_unlock_irq_wake(&lock->wait_lock, wake_q);
if (!owner || !rtmutex_spin_on_owner(lock, waiter, owner))
rt_mutex_schedule();
@ -1799,10 +1787,7 @@ static int __sched rt_mutex_slowlock(struct rt_mutex_base *lock,
*/
raw_spin_lock_irqsave(&lock->wait_lock, flags);
ret = __rt_mutex_slowlock_locked(lock, ww_ctx, state, &wake_q);
preempt_disable();
raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
wake_up_q(&wake_q);
preempt_enable();
raw_spin_unlock_irqrestore_wake(&lock->wait_lock, flags, &wake_q);
rt_mutex_post_schedule();
return ret;
@ -1860,11 +1845,7 @@ static void __sched rtlock_slowlock_locked(struct rt_mutex_base *lock,
owner = rt_mutex_owner(lock);
else
owner = NULL;
preempt_disable();
raw_spin_unlock_irq(&lock->wait_lock);
wake_up_q(wake_q);
wake_q_init(wake_q);
preempt_enable();
raw_spin_unlock_irq_wake(&lock->wait_lock, wake_q);
if (!owner || !rtmutex_spin_on_owner(lock, &waiter, owner))
schedule_rtlock();
@ -1893,10 +1874,7 @@ static __always_inline void __sched rtlock_slowlock(struct rt_mutex_base *lock)
raw_spin_lock_irqsave(&lock->wait_lock, flags);
rtlock_slowlock_locked(lock, &wake_q);
preempt_disable();
raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
wake_up_q(&wake_q);
preempt_enable();
raw_spin_unlock_irqrestore_wake(&lock->wait_lock, flags, &wake_q);
}
#endif /* RT_MUTEX_BUILD_SPINLOCKS */