Messages in this thread | | | Subject | Re: [PATCH v2][RFC] tracing/context-tracking: Add preempt_schedule_context() for tracing | From | Steven Rostedt <> | Date | Wed, 05 Jun 2013 09:41:49 -0400 |
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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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