On Fri, 2013-05-31 at 15:43 +0200, Frederic Weisbecker wrote:
> > +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;
> > +
> > + /*
> > + * 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 = this_cpu_read(context_tracking.state);
> > + user_exit();
>
> You can reuse exception_enter()
I originally did use that, but then noticed that everything else in
context_tracking.c used context_tracking.state directly. I have no
problems doing it this way again.
>
> > + preempt_enable_no_resched_notrace();
> > +
> > + preempt_schedule();
> > +
> > + preempt_disable_notrace();
> > + if (prev_ctx == IN_USER)
> > + user_enter();
>
> And then exception_exit() here.
>
> I guess this replaces your fix with schedule_preempt_user(). I liked
> it because it seems that:
>
> if (need_resched()) {
> user_exit();
> local_irq_enable();
> schedule();
> local_irq_enable();
> user_enter();
> }
>
> is a common pattern of arch user resume preemption that we can consolidate.
>
> But your new patch probably makes it more widely safe for the function tracer
> for any function that can be called and traced in IN_USER mode. Not only user
> preemption.
> Think about do_notify_resume() for example if it is called after
> syscall_trace_leave().
>
> Independantly, schedule_preempt_user() is still interesting for consolidation.
And I think that patch is still valid from just a clean up point of
view. It just didn't cover all the cases needed for tracing.
I'll rewrite the patch and send it out for another review.
Thanks!
-- Steve
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
