linux-kernel - [PATCH] sched/clock: prevent tracing recursion in sched_clock

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Date:	Thu, 06 Mar 2014 14:25:28 +0900
From:	Fernando Luis Vázquez Cao 
	<fernando_b1@....ntt.co.jp>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...nel.org>,
	StevenRostedt <rostedt@...dmis.org>, linux-kernel@...r.kernel.org
Subject: [PATCH] sched/clock: prevent tracing recursion in sched_clock_cpu()

From: Fernando Luis Vazquez Cao <fernando@....ntt.co.jp>

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 <torvalds@...ux-foundation.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Steven Rostedt <rostedt@...dmis.org>
Signed-off-by: Fernando Luis Vazquez Cao <fernando@....ntt.co.jp>
---

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);
 	else
 		clock = sched_clock_local(scd);
-	preempt_enable();
+	preempt_enable_notrace();
 
 	return clock;
 }


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