sched/wait: Fix a kthread race with wait_woken() (cb6538e7) · Commits · 戴 / test

There is a race between kthread_stop() and the new wait_woken() that can result in a lack of progress. CPU 0 | CPU 1 | rfcomm_run() | kthread_stop() ... | if (!test_bit(KTHREAD_SHOULD_STOP)) | | set_bit(KTHREAD_SHOULD_STOP) | wake_up_process() wait_woken() | wait_for_completion() set_current_state(INTERRUPTIBLE) | if (!WQ_FLAG_WOKEN) | schedule_timeout() | | After which both tasks will wait.. forever. Fix this by having wait_woken() check for kthread_should_stop() but only for kthreads (obviously). Signed-off-by:

Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Peter Hurley <peter@hurleysoftware.com> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by:

Ingo Molnar <mingo@kernel.org>

kernel/sched/wait.c

+6 −1

Original line number	Diff line number	Diff line
		@@ -9,6 +9,7 @@
		#include <linux/mm.h>
		#include <linux/wait.h>
		#include <linux/hash.h>
		#include <linux/kthread.h>

		void __init_waitqueue_head(wait_queue_head_t q, const char name, struct lock_class_key *key)
		{
		@@ -297,6 +298,10 @@ int autoremove_wake_function(wait_queue_t wait, unsigned mode, int sync, void
		}
		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);
		@@ -326,7 +331,7 @@ long wait_woken(wait_queue_t *wait, unsigned mode, long timeout)
		* woken_wake_function() such that if we observe WQ_FLAG_WOKEN we must
		* also observe all state before the wakeup.
		*/
		if (!(wait->flags & WQ_FLAG_WOKEN))
		if (!(wait->flags & WQ_FLAG_WOKEN) && !is_kthread_should_stop())
		timeout = schedule_timeout(timeout);
		__set_current_state(TASK_RUNNING);

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