On Mon, 2008-03-10 at 19:12 -0700, Hiroshi Shimamoto wrote: > Peter Zijlstra wrote: > > On Mon, 2008-03-10 at 13:01 -0700, Hiroshi Shimamoto wrote: > > > >> thanks, your patch looks nice to me. > >> I had focused setprio, on_rq=0 and running=1 situation, it makes me to > >> fix these functions. > >> But one point, I've just noticed. I'm not sure on same situation against > >> sched_rt. I think the pre_schedule() of rt has chance to drop rq lock. > >> Is it OK? > > > > Ah, you are quite right, that'll teach me to rush out a patch just > > because dinner is ready :-). > > > > How about we submit the following patch for mainline and CC -stable to > > fix .23 and .24: > > > > Unfortunately, I encountered similar panic with this patch on -rt. > I'll look into this, again. I might have missed something... > > Unable to handle kernel NULL pointer dereference at 0000000000000128 RIP: > [<ffffffff802297f5>] pick_next_task_fair+0x2d/0x42 :-( OK, so that means I'm not getting it. So what does your patch do that mine doesn't? It removes the dependency of running (=task_current()) from on_rq (p->se.on_rq). So how can a current task not be on the runqueue? Only sched.c:dequeue_task() and sched_fair.c:account_entity_dequeue() set on_rq to 0, the only one changing rq->curr is schedule(). So the only scheme I can come up with is that we did dequeue p (on_rq == 0), but we didn't yet schedule so rq->curr == p. Is this how you ended up with your previuos analysis that it must be due to a hole introduced by double_lock_balance()? Because now we can seemingly call deactivate_task() and put_prev_task() in non-atomic fashion, but by placing the put_prev_task() before the load balance calls we should avoid doing that. So what else is going on... /me puzzled -- To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
