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>

diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index 19e5adb49a27d8ae4f586ad88b30faeef0f8e727..acb3b606613eb5b4937cdacab17adc74c4ec2c30 100644 (file)
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -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;
 }