Messages in this thread | | | Date | Tue, 14 May 2013 16:13:07 +0200 | From | Frederic Weisbecker <> | Subject | Re: [PATCH 1/3] x86/sched/context_tracking: Call new schedule_preempt_user() from entry_64.S |
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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.
(Meanwhile I still think it would be a good idea to keep LOCKDEP_SYS_EXIT in the loop :-)
Thanks!
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