Gaurav reported a problem with __kthread_parkme() where a concurrent try_to_wake_up() could result in competing stores to ->state which, when the TASK_PARKED store got lost bad things would happen. The comment near set_current_state() actually mentions this competing store, but only mentions the case against TASK_RUNNING. This same store, with different timing, can happen against a subsequent !RUNNING store. This normally is not a problem, because as per that same comment, the !RUNNING state store is inside a condition based wait-loop: for (;;) { set_current_state(TASK_UNINTERRUPTIBLE); if (!need_sleep) break; schedule(); } __set_current_state(TASK_RUNNING); If we loose the (first) TASK_UNINTERRUPTIBLE store to a previous (concurrent) wakeup, the schedule() will NO-OP and we'll go around the loop once more. The problem here is that the TASK_PARKED store is not inside the KTHREAD_SHOULD_PARK condition wait-loop. There is a genuine issue with sleeps that do not have a condition; this is addressed in a subsequent patch. Reported-by: Gaurav Kohli Signed-off-by: Peter Zijlstra (Intel) --- kernel/kthread.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) --- a/kernel/kthread.c +++ b/kernel/kthread.c @@ -177,12 +177,13 @@ void *kthread_probe_data(struct task_str static void __kthread_parkme(struct kthread *self) { - __set_current_state(TASK_PARKED); - while (test_bit(KTHREAD_SHOULD_PARK, &self->flags)) { + for (;;) { + set_current_state(TASK_PARKED); + if (!test_bit(KTHREAD_SHOULD_PARK, &self->flags)) + break; if (!test_and_set_bit(KTHREAD_IS_PARKED, &self->flags)) complete(&self->parked); schedule(); - __set_current_state(TASK_PARKED); } clear_bit(KTHREAD_IS_PARKED, &self->flags); __set_current_state(TASK_RUNNING);