sched/clock: Prevent tracing recursion in sched_clock_cpu()

Fernando Luis Vazquez Cao · Ingo Molnar · commit 96b3d28bf4b0 · 2014-03-11T11:33:48.000+01:00
Prevent tracing of preempt_disable/enable() in sched_clock_cpu(). When CONFIG_DEBUG_PREEMPT is enabled, preempt_disable/enable() are traced and this causes trace_clock() users (and probably others) to go into an infinite recursion. Systems with a stable sched_clock() are not affected. This problem is similar to that fixed by upstream commit 95ef1e5 ("KVM guest: prevent tracing recursion with kvmclock"). Signed-off-by: Fernando Luis Vazquez Cao <fernando@oss.ntt.co.jp> Signed-off-by: Peter Zijlstra <peterz@infradead.org> Acked-by: Steven Rostedt <rostedt@goodmis.org> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Link: http://lkml.kernel.org/r/1394083528.4524.3.camel@nexus Signed-off-by: Ingo Molnar <mingo@kernel.org>
diff --git a/kernel/sched/clock.c b/kernel/sched/clock.c
@@ -301,14 +301,14 @@ u64 sched_clock_cpu(int cpu)
 	if (unlikely(!sched_clock_running))
 		return 0ull;
 
-	preempt_disable();
+	preempt_disable_notrace();
 	scd = cpu_sdc(cpu);
 
 	if (cpu != smp_processor_id())
 		clock = sched_clock_remote(scd);
 	else
 		clock = sched_clock_local(scd);
-	preempt_enable();
+	preempt_enable_notrace();
 
 	return clock;
 }
