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Date:	Thu, 6 Mar 2014 05:51:13 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Fernando Luis Vázquez Cao 
	<fernando_b1@....ntt.co.jp>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sched/clock: prevent tracing recursion in
 sched_clock_cpu()

On Thu, 06 Mar 2014 14:25:28 +0900
Fernando Luis Vázquez Cao <fernando_b1@....ntt.co.jp> wrote:

> From: Fernando Luis Vazquez Cao <fernando@....ntt.co.jp>
> 
> Prevent tracing of preempt_disable/enable() in sched_clock_cpu().
> When CONFIG_DEBUG_PREEMPT is enabled, preempt_disable/enable() are
> traced and this causes trace_clock() users (and probably others) to
> go into an infinite recursion. Systems with a stable sched_clock()
> are not affected.
> 
> This problem is similar to that fixed by upstream commit 95ef1e52922
> ("KVM guest: prevent tracing recursion with kvmclock").

Also similar to: 569d6557ab957.

Acked-by: Steven Rostedt <rostedt@...dmis.org>

-- Steve

> 
> Cc: Linus Torvalds <torvalds@...ux-foundation.org>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Ingo Molnar <mingo@...nel.org>
> Cc: Steven Rostedt <rostedt@...dmis.org>
> Signed-off-by: Fernando Luis Vazquez Cao <fernando@....ntt.co.jp>
> ---
> 
> diff -urNp linux-3.14-rc5-orig/kernel/sched/clock.c linux-3.14-rc5/kernel/sched/clock.c
> --- linux-3.14-rc5-orig/kernel/sched/clock.c	2014-03-06 13:37:43.567720550 +0900
> +++ linux-3.14-rc5/kernel/sched/clock.c	2014-03-06 13:41:56.937100949 +0900
> @@ -301,14 +301,14 @@ u64 sched_clock_cpu(int cpu)
>  	if (unlikely(!sched_clock_running))
>  		return 0ull;
>  
> -	preempt_disable();
> +	preempt_disable_notrace();
>  	scd = cpu_sdc(cpu);
>  
>  	if (cpu != smp_processor_id())
>  		clock = sched_clock_remote(scd);
>  	else
>  		clock = sched_clock_local(scd);
> -	preempt_enable();
> +	preempt_enable_notrace();
>  
>  	return clock;
>  }
> 

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