Messages in this thread | | | Subject | Re: [PATCH v2][RFC] tracing/context-tracking: Add preempt_schedule_context() for tracing | From | Steven Rostedt <> | Date | Tue, 04 Jun 2013 08:16:29 -0400 |
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On Tue, 2013-06-04 at 14:09 +0200, Frederic Weisbecker wrote: > > > +/** > > + * preempt_schedule_context - preempt_schedule called by tracing > > + * > > + * The tracing infrastructure uses preempt_enable_notrace to prevent > > + * recursion and tracing preempt enabling caused by the tracing > > + * infrastructure itself. But as tracing can happen in areas coming > > + * from userspace or just about to enter userspace, a preempt enable > > + * can occur before user_exit() is called. This will cause the scheduler > > + * to be called when the system is still in usermode. > > + * > > + * To prevent this, the preempt_enable_notrace will use this function > > + * instead of preempt_schedule() to exit user context if needed before > > + * calling the scheduler. > > + */ > > +void __sched notrace preempt_schedule_context(void) > > +{ > > + struct thread_info *ti = current_thread_info(); > > + enum ctx_state prev_ctx; > > + > > + if (likely(ti->preempt_count || irqs_disabled())) > > + return; > > or: > if (!preemptible()) > return;
Sure, but this is a cut and paste from preempt_schedule(). If I make that change here, I would want to make that there too.
Peter, should I use !preemptible() or keep it like preempt_schedule() and make a clean up change for 3.11?
> > > + > > + /* > > + * Need to disable preemption in case user_exit() is traced > > + * and the tracer calls preempt_enable_notrace() causing > > + * an infinite recursion. > > + */ > > + preempt_disable_notrace(); > > + prev_ctx = exception_enter(); > > + preempt_enable_no_resched_notrace(); > > + > > + preempt_schedule(); > > + > > + preempt_disable_notrace(); > > + exception_exit(prev_ctx); > > + preempt_enable_notrace(); > > +} > > +EXPORT_SYMBOL(preempt_schedule_context); > > That's quite a tricky change but I can't think of anything better.
Yeah, I had a few other solutions that were even worse than this one. Then I finally decided this was the best of the worse.
> > Acked-by: Frederic Weisbecker <fweisbec@gmail.com>
Thanks,
-- Steve
> > > > /** > > * user_exit - Inform the context tracking that the CPU is > > -- > > 1.7.3.4 > > > > > >
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