linux-kernel - Re: [PATCH 3/4] tracing: Add stack_tracer

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Message-Id: <20170406220821.GN1600@linux.vnet.ibm.com>
Date:   Thu, 6 Apr 2017 15:08:21 -0700
From:   "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 3/4] tracing: Add stack_tracer_disable/enable() functions

On Thu, Apr 06, 2017 at 05:23:48PM -0400, Steven Rostedt wrote:
> On Thu, 6 Apr 2017 13:21:17 -0700
> "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> wrote:
> 
> > > My worry is that we add another caller that doesn't disable interrupts
> > > or preemption.
> > > 
> > > I could add a __stack_trace_disable() that skips the disabling of
> > > preemption, as the "__" usually denotes the call is "special".  
> > 
> > Given that interrupts are disabled at that point, and given also that
> > NMI skips stack tracing if growth is required, could we just leave
> > out the stack_tracer_disable() and stack_tracer_enable()?
> 
> There may be other use cases. Hmm, maybe I'll just have it do a check
> to make sure preemption is disabled. Something like:
> 
> 	if (IS_ENABLED(CONFIG_DEBUG_PREEMPT))
> 		WARN_ON_ONCE(!preempt_count());

This in the include/linux/ftrace.h file so that it can be inlined?
That makes sense to me.

							Thanx, Paul