On Mon, Jul 15, 2013 at 06:14:34PM +0400, Kirill Tkhai wrote: > >> > >> #ifdef CONFIG_SMP > >> + p->state = TASK_WAKING; > >> + smp_wmb(); > >> + > > > > This too is broken; the loop below needs to be completed first, > > otherwise we change p->state while the task is still on the CPU and it > > might read the wrong p->state. > > This place is below (on_rq && ttwu_remote) check, so the task > either 'dequeued and on_cpu == 0' > or it's in the middle of schedule() on arch, which wants unlocked > context switch. > > Nobody scheduler's probes p->state between prepare_lock_switch() and > finish_lock_switch(). Archs with unlocked ctx switch (mips and ia64) > don't change or probe state of previous process during context_switch.
It means its after deactivate_task(), but before context_switch(). It so happens that context_switch()->prepare_task_switch()->trace_sched_switch() inspects p->state. Even if this was not the case, touching a task that is 'life' on another CPU is very _very_ bad practise. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
