Re: [PATCH] kthread: Prevent unpark race which puts threads on thewrong cpu

From: Thomas Gleixner
Date: Thu Apr 11 2013 - 15:48:33 EST


On Thu, 11 Apr 2013, Dave Hansen wrote:
> On 04/11/2013 03:19 AM, Thomas Gleixner wrote:
> > --- linux-2.6.orig/kernel/smpboot.c
> > +++ linux-2.6/kernel/smpboot.c
> > @@ -185,8 +185,18 @@ __smpboot_create_thread(struct smp_hotpl
> > }
> > get_task_struct(tsk);
> > *per_cpu_ptr(ht->store, cpu) = tsk;
> > - if (ht->create)
> > - ht->create(cpu);
> > + if (ht->create) {
> > + /*
> > + * Make sure that the task has actually scheduled out
> > + * into park position, before calling the create
> > + * callback. At least the migration thread callback
> > + * requires that the task is off the runqueue.
> > + */
> > + if (!wait_task_inactive(tsk, TASK_PARKED))
> > + WARN_ON(1);
> > + else
> > + ht->create(cpu);
> > + }
> > return 0;
> > }
>
> This one appears to be doing the trick. I'll run the cpus in an
> online/offline loop for a bit and make sure it's stable. It's passed
> several round so far, which is way more than it's done up to this point,
> though.

I think the most critical part is bootup when the threads are
created. The online/offline one is an issue as well, which is covered
by the patches, but way harder to trigger.

Thanks,

tglx


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