On Tue, Apr 22, 2014 at 10:10:52AM -0700, [email protected] wrote: > This is all expected behavior, and the somewhat less than useful trace > events are expected. A task setting p->state to TASK_RUNNING without > locks is fine if and only p == current. The standard deschedule loop is > basically: > > while (1) { > set_current_state(TASK_(UN)INTERRUPTIBLE); > if (should_still_sleep) > schedule(); > } > set_current_state(TASK_RUNNING); > > Which can produce this in a race. > > The only problem this causes is a wasted check_preempt_curr call in the > racing case, and a somewhat inaccurate sched:sched_wakeup trace event. > Note that even if you did recheck in ttwu_do_wakeup you could still race > and get an "inaccurate" trace event. Heck, even if the ttwu is > _necessary_ because p is currently trying to take rq->lock to > deschedule, you won't get a matching sched_switch event, because the > ttwu is running before schedule is. > > You could sorta fix this I guess by tracking every write to p->state > with trace events, but that would be a somewhat different change, and > might be considered too expensive for all I know (and the trace events > could /still/ be resolved in a different order across cpus compared to > p->state's memory).
Ah, you're saying that a second task could try a spurious wakeup between set_current_state() and schedule(). Yes, that'll trigger this indeed. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
