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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: Steven Rostedt <rostedt@goodmis.org>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/20140204141315.2a968a72@gandalf.local.home
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Steven Rostedt 2014-02-04 14:13:15 -05:00 committed by Ingo Molnar
parent 494479038d
commit 569d6557ab
1 changed files with 2 additions and 2 deletions
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4
arch/x86/kernel/tsc.c
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@ -209,7 +209,7 @@ static inline unsigned long long cycles_2_ns(unsigned long long cyc)
* dance when its actually needed.
*/
preempt_disable();
preempt_disable_notrace();
data = this_cpu_read(cyc2ns.head);
tail = this_cpu_read(cyc2ns.tail);
@ -229,7 +229,7 @@ static inline unsigned long long cycles_2_ns(unsigned long long cyc)
if (!--data->__count)
this_cpu_write(cyc2ns.tail, data);
}
preempt_enable();
preempt_enable_notrace();
return ns;
}