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From: Corey Minyard <cminyard@mvista.com>
Date: Thu, 9 May 2019 14:33:20 -0500
Subject: [PATCH 264/342] sched/completion: Fix a lockup in
wait_for_completion()
Origin: https://git.kernel.org/cgit/linux/kernel/git/rt/linux-stable-rt.git/commit?id=83dfd5e7c7759d10ab5260a4ed98cdd46efa7213
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: stable-rt@vger.kernel.org
Fixes: a04ff6b4ec4ee7e ("completion: Use simple wait queues")
Signed-off-by: Corey Minyard <cminyard@mvista.com>
Acked-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
[bigeasy: shorten commit message ]
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
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);
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