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Date:	Thu, 06 Mar 2014 14:25:28 +0900
From:	Fernando Luis Vázquez Cao 
To:	Peter Zijlstra <>
Cc:	Linus Torvalds <>,
	Andrew Morton <>,
	Ingo Molnar <>,
	StevenRostedt <>,
Subject: [PATCH] sched/clock: prevent tracing recursion in sched_clock_cpu()

From: Fernando Luis Vazquez Cao <>

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").

Cc: Linus Torvalds <>
Cc: Andrew Morton <>
Cc: Ingo Molnar <>
Cc: Steven Rostedt <>
Signed-off-by: Fernando Luis Vazquez Cao <>

diff -urNp linux-3.14-rc5-orig/kernel/sched/clock.c linux-3.14-rc5/kernel/sched/clock.c
--- linux-3.14-rc5-orig/kernel/sched/clock.c	2014-03-06 13:37:43.567720550 +0900
+++ linux-3.14-rc5/kernel/sched/clock.c	2014-03-06 13:41:56.937100949 +0900
@@ -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);
 		clock = sched_clock_local(scd);
-	preempt_enable();
+	preempt_enable_notrace();
 	return clock;

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