sched/clock: Prevent tracing recursion in sched_clock_cpu()

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 95ef1e52922
("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>

1 files changed, 2 insertions, 2 deletions

diff --git a/kernel/sched/clock.c b/kernel/sched/clock.c
index 43c2bcc35761..b30a2924ef14 100644
--- 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;
 }