Messages in this thread Patch in this message | | | Date | Fri, 31 Oct 2014 12:10:38 +0100 | From | Peter Zijlstra <> | Subject | [PATCH 1/7] sched,wait: Fix a kthread race with wait_woken() |
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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).
Cc: Peter Hurley <peter@hurleysoftware.com> Cc: Oleg Nesterov <oleg@redhat.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> --- kernel/sched/wait.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-)
--- a/kernel/sched/wait.c +++ b/kernel/sched/wait.c @@ -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_ } 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, unsi * 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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