x86: Use preempt_disable_notrace() in cycles_2_ns()
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: NSteven Rostedt <rostedt@goodmis.org> Acked-by: NThomas Gleixner <tglx@linutronix.de> Signed-off-by: NPeter Zijlstra <peterz@infradead.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Link: http://lkml.kernel.org/r/20140204141315.2a968a72@gandalf.local.homeSigned-off-by: NIngo Molnar <mingo@kernel.org>
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