Messages in this thread Patch in this message | | | Date | Tue, 21 Jul 2020 00:52:52 -0400 | From | Paul Gortmaker <> | Subject | Re: 5.8-rc*: kernel BUG at kernel/signal.c:1917 |
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[Re: 5.8-rc*: kernel BUG at kernel/signal.c:1917] On 20/07/2020 (Mon 16:21) Peter Zijlstra wrote:
> On Mon, Jul 20, 2020 at 04:02:24PM +0200, Oleg Nesterov wrote: > > I have to admit, I do not understand the usage of prev_state in schedule(), > > it looks really, really subtle... > > Right, so commit dbfb089d360 solved a problem where schedule() re-read > prev->state vs prev->on_rq = 0. That is, schedule()'s dequeue and > ttwu()'s enqueue disagreed over sched_contributes_to_load. and as a > result load-accounting went wobbly. > > Now, looking at that commit again, I might've solved the problem twice > :-P
[...]
> That said, in a crossed email, I just proposed we could simplify all > this like so.. but now I need to go ask people to re-validate that > loadavg muck again :-/
After a two hour "quick" sanity test I then gave it a full 7h run (which always seemed to break before dbfb089d360) and I didn't see any stuck load average with master from today + this change.
Paul.
root@t5610:/home/paul/git/linux-head# [1]+ Done nohup tools/testing/selftests/rcutorture/bin/kvm.sh --cpus 24 --duration 420 --configs TREE03 --trust-make > /tmp/kvm.sh.out 2>&1 root@t5610:/home/paul/git/linux-head# cat /proc/version Linux version 5.8.0-rc6-00001-g5714ee50bb43-dirty (paul@t5610) (gcc (Ubuntu 9.3.0-10ubuntu2) 9.3.0, GNU ld (GNU Binutils for Ubuntu) 2.34) #3 SMP Mon Jul 20 12:30:33 EDT 2020 root@t5610:/home/paul/git/linux-head# uptime 00:49:18 up 7:41, 2 users, load average: 0.01, 0.00, 0.63 root@t5610:/home/paul/git/linux-head#
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> > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index a2a244af9a53..437fc3b241f2 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -4193,9 +4193,6 @@ static void __sched notrace __schedule(bool preempt) > local_irq_disable(); > rcu_note_context_switch(preempt); > > - /* See deactivate_task() below. */ > - prev_state = prev->state; > - > /* > * Make sure that signal_pending_state()->signal_pending() below > * can't be reordered with __set_current_state(TASK_INTERRUPTIBLE) > @@ -4223,7 +4220,8 @@ static void __sched notrace __schedule(bool preempt) > * We must re-load prev->state in case ttwu_remote() changed it > * before we acquired rq->lock. > */ > - if (!preempt && prev_state && prev_state == prev->state) { > + prev_state = prev->state; > + if (!preempt && prev_state) { > if (signal_pending_state(prev_state, prev)) { > prev->state = TASK_RUNNING; > } else { > @@ -4237,10 +4235,12 @@ static void __sched notrace __schedule(bool preempt) > > /* > * __schedule() ttwu() > - * prev_state = prev->state; if (READ_ONCE(p->on_rq) && ...) > - * LOCK rq->lock goto out; > - * smp_mb__after_spinlock(); smp_acquire__after_ctrl_dep(); > - * p->on_rq = 0; p->state = TASK_WAKING; > + * if (prev_state) if (p->on_rq && ...) > + * p->on_rq = 0; goto out; > + * smp_acquire__after_ctrl_dep(); > + * p->state = TASK_WAKING > + * > + * Where __schedule() and ttwu() have matching control dependencies. > * > * After this, schedule() must not care about p->state any more. > */
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