4.19.37-rt20-rc1 stable review patch. If anyone has any objections, please let me know.
------------------ From: Corey Minyard <[email protected]> Consider following race: T0 T1 T2 wait_for_completion() do_wait_for_common() __prepare_to_swait() schedule() complete() x->done++ (0 -> 1) raw_spin_lock_irqsave() swake_up_locked() wait_for_completion() wake_up_process(T0) list_del_init() raw_spin_unlock_irqrestore() raw_spin_lock_irq(&x->wait.lock) raw_spin_lock_irq(&x->wait.lock) x->done != UINT_MAX, 1 -> 0 raw_spin_unlock_irq(&x->wait.lock) return 1 while (!x->done && timeout), continue loop, not enqueued on &x->wait Basically, the problem is that the original wait queues used in completions did not remove the item from the queue in the wakeup function, but swake_up_locked() does. Fix it by adding the thread to the wait queue inside the do loop. The design of swait detects if it is already in the list and doesn't do the list add again. Cc: [email protected] Fixes: a04ff6b4ec4ee7e ("completion: Use simple wait queues") Signed-off-by: Corey Minyard <[email protected]> Acked-by: Steven Rostedt (VMware) <[email protected]> Signed-off-by: Steven Rostedt (VMware) <[email protected]> [bigeasy: shorten commit message ] Signed-off-by: Sebastian Andrzej Siewior <[email protected]> --- kernel/sched/completion.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/sched/completion.c b/kernel/sched/completion.c index 755a58084978..49c14137988e 100644 --- a/kernel/sched/completion.c +++ b/kernel/sched/completion.c @@ -72,12 +72,12 @@ do_wait_for_common(struct completion *x, if (!x->done) { DECLARE_SWAITQUEUE(wait); - __prepare_to_swait(&x->wait, &wait); do { if (signal_pending_state(state, current)) { timeout = -ERESTARTSYS; break; } + __prepare_to_swait(&x->wait, &wait); __set_current_state(state); raw_spin_unlock_irq(&x->wait.lock); timeout = action(timeout); -- 2.20.1
