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 <fweis...@gmail.com>
Thanks,
-- Steve
>
>
> > /**
> > * user_exit - Inform the context tracking that the CPU is
> > --
> > 1.7.3.4
> >
> >
> >
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