Re: [PATCH] x86: Use preempt_disable_notrace() in cycles_2_ns()

From: Peter Zijlstra
Date: Tue Feb 04 2014 - 14:46:19 EST

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@xxxxxxxxxxx>

Indeed, thanks!
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