On Wed, 2013-06-05 at 13:45 +0200, Peter Zijlstra wrote:
> On Tue, Jun 04, 2013 at 10:16:56AM -0400, Steven Rostedt wrote:
> > index 65349f0..73b89d9 100644
> > --- a/kernel/context_tracking.c
> > +++ b/kernel/context_tracking.c
> > @@ -71,6 +71,46 @@ void user_enter(void)
> > local_irq_restore(flags);
> > }
> >
> > +#ifdef CONFIG_PREEMPT
> > +/**
> > + * 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.
> > + */
>
> If preempt_enable_notrace() is the only user, why does this live in
> kernel/context_tracking.c and not in kernel/sched/core.c?
Then we would need to add #ifdef CONFIG_CONTEXT_TRACKING around it too.
As we have in preempt.h:
#ifdef CONFIG_CONTEXT_TRACKING
void preempt_schedule_context(void);
#define preempt_check_resched_context() \
do { \
if (unlikely(test_thread_flag(TIF_NEED_RESCHED))) \
preempt_schedule_context(); \
} while(0)
#else
#define preempt_check_resched_context() preempt_check_resched()
#endif
Seemed like it was more appropriate to be in context_tracking.c than
sched/core.c, as it depends on context tracking.
>
> > +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 = exception_enter();
> > + preempt_enable_no_resched_notrace();
> > +
> > + preempt_schedule();
> > +
> > + preempt_disable_notrace();
> > + exception_exit(prev_ctx);
> > + preempt_enable_notrace();
> > +}
> > +EXPORT_SYMBOL(preempt_schedule_context);
>
> Do we really need to export this?
As preempt_enable_notrace() is also used by tracepoints, yes. Because
tracepoints are used by modules. Hmm, now it may be exported via a GPL
export though.
-- Steve
>
> > +#endif /* CONFIG_PREEMPT */
> >
> > /**
> > * user_exit - Inform the context tracking that the CPU is
> > --
> > 1.7.10.4
> >
> >
> >
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