From: Peter Zijlstra <peterz@infradead.org>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: LKML <linux-kernel@vger.kernel.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@kernel.org>,
"H. Peter Anvin" <hpa@linux.intel.com>
Subject: Re: [PATCH] x86: Use preempt_disable_notrace() in cycles_2_ns()
Date: Tue, 4 Feb 2014 20:45:56 +0100 [thread overview]
Message-ID: <20140204194556.GE5002@laptop.programming.kicks-ass.net> (raw)
In-Reply-To: <20140204141315.2a968a72@gandalf.local.home>
On Tue, Feb 04, 2014 at 02:13:15PM -0500, Steven Rostedt wrote:
> When debug preempt is enabled, preempt_disable() can be traced by
> function and function graph tracing.
>
> There's a place in the function graph tracer that calls trace_clock()
> which eventually calls cycles_2_ns() outside of the recursion
> protection. When cycles_2_ns() calls preempt_disable() it gets traced
> and the graph tracer will go into a recursive loop causing a crash or
> worse, a triple fault.
>
> Simple fix is to use preempt_disable_notrace() in cycles_2_ns, which
> makes sense because the preempt_disable() tracing may use that code
> too, and it tracing it, even with recursion protection is rather
> pointless.
>
> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Indeed, thanks!
next prev parent reply other threads:[~2014-02-04 19:46 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-02-04 19:13 [PATCH] x86: Use preempt_disable_notrace() in cycles_2_ns() Steven Rostedt
2014-02-04 19:45 ` Peter Zijlstra [this message]
2014-02-04 20:22 ` Thomas Gleixner
2014-02-10 13:28 ` [tip:x86/urgent] " tip-bot for Steven Rostedt
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