Re: [ANNOUNCE] v4.11.5-rt1
From: Steven Rostedt
Date: Mon Jun 19 2017 - 10:08:46 EST
On Mon, 19 Jun 2017 12:14:51 +0200
Mike Galbraith <efault@xxxxxx> wrote:
> On Mon, 2017-06-19 at 10:52 +0200, Sebastian Andrzej Siewior wrote:
> > On 2017-06-17 10:14:37 [+0200], Mike Galbraith wrote:
> > > During that rebase, migrate_disable() was changed to no longer map to
> > > preempt_disable() for nonrt, but some patches still assume it does. ÂIt
> > > now depends upon PREEMPT_COUNT, the RT workaround in futex.c induces
> > > grumbling in nonrt builds with PREEMPT_COUNT enabled.
> > argh, right. It was planned to get it merged upstream but due to
> > $reasons we never got that far. For that reason I would simply revert
> > that change and let migrate_disable() map to preempt_disable() as it did
> > earlier.
> Ok, doesn't matter for RT testing. What does matter, is that...
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 30b24f774198..10e832da70b6 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -2284,7 +2284,7 @@ EXPORT_SYMBOL(wake_up_process);
> int wake_up_lock_sleeper(struct task_struct *p)
> - return try_to_wake_up(p, TASK_ALL, WF_LOCK_SLEEPER);
> + return try_to_wake_up(p, TASK_UNINTERRUPTIBLE, WF_LOCK_SLEEPER);
> ...appears to be inducing lost futex wakeups.
Hmm, it shouldn't affect futexes, as it's only called by rtmutex when
waiter->savestate is true. And that should always be false for futex.
> Scratch that "appears", changing it to TASK_NORMAL just fixed my DL980
> running otherwise absolutely pristine 4.9-rt21, after having double
> verified that rt20 works fine. ÂNow to go back to 4.11/master/tip-rt,
> make sure that the little bugger really really REALLY ain't fscking
> with me for the sheer fun of it, futexes being made of pure evil :)
> My testcase is to run futex_wait -n 4 in a modest sized loop. ÂOdd
> thing is that it only reproduces on the DL980 if I let it use multiple
> sockets, pin it to one, and all is peachy, (rather seems to be given)
> whereas on desktop box, the hang is far more intermittent, but there.