On Tue, 2013-05-14 at 16:13 +0200, Frederic Weisbecker wrote:
> On Fri, May 10, 2013 at 05:12:26PM -0400, Steven Rostedt wrote:
> > +/*
> > + * This is a entry point to the scheduler() just before going
> > + * back to user space. This is called with irqs disabled
> > + * which prevents races with the CONTEXT_TRACKING updates.
> > + */
> > +asmlinkage void __sched schedule_preempt_user(void)
> > +{
> > + enum ctx_state prev_state;
> > +
> > + prev_state = exception_enter();
> > +
> > + local_irq_enable();
> > + __schedule();
> > + local_irq_disable();
> > +
> > + exception_exit(prev_state);
> > +}
>
> Ok I just had a look at how ARM and PPC64 are handling user preemption and it
> seems
> that irqs are disabled around the call to schedule() on these archs too.
> Although
> do_work_pending() in ARM surprisingly doesn't re-enable irqs before calling
> schedule?
>
> Anyway having irqs disabled around user preemption seem to be a requirement
> to make
> sure the TIF_NEED_RESCHED check is not racy against irqs and return to
> userspace.
> So I guess we can keep the above function as it is.
>
> But perhaps we should queue this for 3.11 given that it's a bit of a
> sensitive change
> in the x86 user return path.
>
> Look, I'm just going to make a seperate pull request with this patch based on
> 3.10-rc1
> and let Ingo choose the target.
Could the deletion of schedule_user() be separated to another patch. So
for other archs, such as ppc64, we could have both
schedule_preempt_user() and schedule_user() there for the conversion?
Or are there some better ways to avoid the conflict with arch trees?
Thanks, Zhong
>
> (Meanwhile I still think it would be a good idea to keep LOCKDEP_SYS_EXIT in
> the loop :-)
>
> Thanks!
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