Commit ef73d6a4 authored by Arve Hjønnevåg's avatar Arve Hjønnevåg Committed by Peter Zijlstra
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sched/wait: Fix a kthread_park race with wait_woken() 



kthread_park and wait_woken have a similar race that
kthread_stop and wait_woken used to have before it was fixed in
commit cb6538e7 ("sched/wait: Fix a kthread race with
wait_woken()"). Extend that fix to also cover kthread_park.

[jstultz: Made changes suggested by Peter to optimize
 memory loads]

Signed-off-by: default avatarArve Hjønnevåg <arve@android.com>
Signed-off-by: default avatarJohn Stultz <jstultz@google.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: default avatarValentin Schneider <vschneid@redhat.com>
Link: https://lore.kernel.org/r/20230602212350.535358-1-jstultz@google.com
parent 0cce0fde

include/linux/kthread.h

+1 −0
Original line number Diff line number Diff line
@@ -89,6 +89,7 @@ int kthread_stop(struct task_struct *k); 
bool kthread_should_stop(void);

bool kthread_should_park(void);

bool __kthread_should_park(struct task_struct *k);

bool kthread_should_stop_or_park(void);

bool kthread_freezable_should_stop(bool *was_frozen);

void *kthread_func(struct task_struct *k);

void *kthread_data(struct task_struct *k);

kernel/kthread.c

+10 −0
Original line number Diff line number Diff line
@@ -182,6 +182,16 @@ bool kthread_should_park(void) 
}

EXPORT_SYMBOL_GPL(kthread_should_park);



bool kthread_should_stop_or_park(void)

{

	struct kthread *kthread = __to_kthread(current);



	if (!kthread)

		return false;



	return kthread->flags & (BIT(KTHREAD_SHOULD_STOP) | BIT(KTHREAD_SHOULD_PARK));

}



/**

 * kthread_freezable_should_stop - should this freezable kthread return now?

 * @was_frozen: optional out parameter, indicates whether %current was frozen

kernel/sched/wait.c

+1 −6
Original line number Diff line number Diff line
@@ -425,11 +425,6 @@ int autoremove_wake_function(struct wait_queue_entry *wq_entry, unsigned mode, i 
}

EXPORT_SYMBOL(autoremove_wake_function);



static inline bool is_kthread_should_stop(void)

{

	return (current->flags & PF_KTHREAD) && kthread_should_stop();

}



/*

 * DEFINE_WAIT_FUNC(wait, woken_wake_func);

 *
@@ -459,7 +454,7 @@ long wait_woken(struct wait_queue_entry *wq_entry, unsigned mode, long timeout) 
	 * or woken_wake_function() sees our store to current->state.

	 */

	set_current_state(mode); /* A */

	if (!(wq_entry->flags & WQ_FLAG_WOKEN) && !is_kthread_should_stop())

	if (!(wq_entry->flags & WQ_FLAG_WOKEN) && !kthread_should_stop_or_park())

		timeout = schedule_timeout(timeout);

	__set_current_state(TASK_RUNNING);