On Wed, 02 Jun 2021, Peter Zijlstra wrote:
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(); ,-----> ,' (OoO load, observed !COND)
| |
| | COND = 1;
| `- if (t->state != RUNNING)
| wake_up_process(t); // not done
if (COND) ---------'
break;
schedule(); // forever waiting
}
t->state = TASK_RUNNING;
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Reviewed-by: Davidlohr Bueso <dbueso@xxxxxxx>
