linux-kernel - [tip:sched/core] sched/clock: Prevent tracing recursion in sched_clock

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Date:	Tue, 11 Mar 2014 05:36:58 -0700
From:	tip-bot for Fernando Luis Vazquez Cao <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, hpa@...or.com, mingo@...nel.org,
	torvalds@...ux-foundation.org, peterz@...radead.org,
	rostedt@...dmis.org, akpm@...ux-foundation.org,
	fernando@....ntt.co.jp, tglx@...utronix.de
Subject: [tip:sched/core] sched/clock:
  Prevent tracing recursion in sched_clock_cpu()

Commit-ID:  96b3d28bf4b00f62fc8386ff5d487d1830793a3d
Gitweb:     http://git.kernel.org/tip/96b3d28bf4b00f62fc8386ff5d487d1830793a3d
Author:     Fernando Luis Vazquez Cao <fernando@....ntt.co.jp>
AuthorDate: Thu, 6 Mar 2014 14:25:28 +0900
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Tue, 11 Mar 2014 11:33:48 +0100

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@....ntt.co.jp>
Signed-off-by: Peter Zijlstra <peterz@...radead.org>
Acked-by: Steven Rostedt <rostedt@...dmis.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Link: http://lkml.kernel.org/r/1394083528.4524.3.camel@nexus
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 kernel/sched/clock.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/clock.c b/kernel/sched/clock.c
index 43c2bcc..b30a292 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;
 }
--
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