From cb6538e740d7543cd989128625cf8cac4b471e0a Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Fri, 31 Oct 2014 11:57:30 +0100 Subject: [PATCH] sched/wait: Fix a kthread race with wait_woken() 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) Cc: Peter Hurley Cc: Oleg Nesterov Cc: Linus Torvalds Signed-off-by: Ingo Molnar --- kernel/sched/wait.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/kernel/sched/wait.c b/kernel/sched/wait.c index 4dae188..852143a 100644 --- a/kernel/sched/wait.c +++ b/kernel/sched/wait.c @@ -9,6 +9,7 @@ #include #include #include +#include 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); -- 2.7.4