16.07.2013, 00:19, "Peter Zijlstra" <pet...@infradead.org>: > 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.
Thanks for the explanation. Kirill -- 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/
