Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754643Ab3FELqM (ORCPT ); Wed, 5 Jun 2013 07:46:12 -0400 Received: from merlin.infradead.org ([205.233.59.134]:49586 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752441Ab3FELqK (ORCPT ); Wed, 5 Jun 2013 07:46:10 -0400 Date: Wed, 5 Jun 2013 13:45:59 +0200 From: Peter Zijlstra To: Steven Rostedt Cc: Frederic Weisbecker , LKML , "Paul E. McKenney" , Dave Jones , Ingo Molnar Subject: Re: [PATCH v2][RFC] tracing/context-tracking: Add preempt_schedule_context() for tracing Message-ID: <20130605114559.GE8923@twins.programming.kicks-ass.net> References: <1369943981.26799.43.camel@gandalf.local.home> <20130531134319.GE5932@somewhere> <1370013528.26799.49.camel@gandalf.local.home> <20130531160101.GB5910@twins.programming.kicks-ass.net> <1370050218.26799.87.camel@gandalf.local.home> <20130604122712.GE14973@somewhere> <1370355416.26799.119.camel@gandalf.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1370355416.26799.119.camel@gandalf.local.home> User-Agent: Mutt/1.5.21 (2012-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2159 Lines: 68 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 > > > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/