linux-kernel - Re: [PATCH v2][RFC] tracing/context-tracking: Add preempt_schedule

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Message-ID: <20130604122919.GF14973@somewhere>
Date:	Tue, 4 Jun 2013 14:29:20 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	LKML <linux-kernel@...r.kernel.org>,
	"Paul E. McKenney" <paulmck@...ibm.com>,
	Dave Jones <davej@...hat.com>, Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH v2][RFC] tracing/context-tracking: Add
 preempt_schedule_context() for tracing

On Tue, Jun 04, 2013 at 08:16:29AM -0400, Steven Rostedt wrote:
> On Tue, 2013-06-04 at 14:09 +0200, Frederic Weisbecker wrote:
> >  
> > > +/**
> > > + * 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.
> > > + */
> > > +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;
> > 
> > or:
> >         if (!preemptible())
> >                 return;
> 
> Sure, but this is a cut and paste from preempt_schedule(). If I make
> that change here, I would want to make that there too.
> 
> Peter, should I use !preemptible() or keep it like preempt_schedule()
> and make a clean up change for 3.11?

That seem to indeed make sense to use it in preempt_schedule() as well.
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