Messages in this thread | | | Date | Wed, 5 Jun 2013 13:45:59 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH v2][RFC] tracing/context-tracking: Add preempt_schedule_context() for tracing |
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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?
> +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?
> +#endif /* CONFIG_PREEMPT */ > > /** > * user_exit - Inform the context tracking that the CPU is > -- > 1.7.10.4 > > >
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