sched: Unbreak wakeups
Remove broken task->state references and let wake_up_process() DTRT.
The anti-pattern in these patches breaks the ordering of ->state vs
COND as described in the comment near set_current_state() and can lead
to missed wakeups:
(OoO load, observes RUNNING)<-.
for (;;) { |
t->state = UNINTERRUPTIBLE; |
smp_mb(); ,-----> | (observes !COND)
| /
if (COND) ---------' | COND = 1;
break; `- if (t->state != RUNNING)
wake_up_process(t); // not done
schedule(); // forever waiting
}
t->state = TASK_RUNNING;
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Davidlohr Bueso <dbueso@suse.de>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/20210611082838.160855222@infradead.org
diff --git a/kernel/softirq.c b/kernel/softirq.c
index 4992853..5ddc3b15 100644
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -76,7 +76,7 @@ static void wakeup_softirqd(void)
/* Interrupts are disabled: no need to stop preemption */
struct task_struct *tsk = __this_cpu_read(ksoftirqd);
- if (tsk && tsk->state != TASK_RUNNING)
+ if (tsk)
wake_up_process(tsk);
}
