4.14-stable review patch. If anyone has any objections, please let me know.
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From: Peter Zijlstra peterz@infradead.org
[ Upstream commit 741a76b350897604c48fb12beff1c9b77724dc96 ]
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 gkohli@codeaurora.org Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Reviewed-by: Oleg Nesterov oleg@redhat.com Cc: Linus Torvalds torvalds@linux-foundation.org Cc: Peter Zijlstra peterz@infradead.org Cc: Thomas Gleixner tglx@linutronix.de Signed-off-by: Ingo Molnar mingo@kernel.org Signed-off-by: Sasha Levin alexander.levin@microsoft.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- kernel/kthread.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-)
--- a/kernel/kthread.c +++ b/kernel/kthread.c @@ -169,12 +169,13 @@ 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);