linux-kernel - [PATCH] sched: Fix preempt_schedule_common() triggering tracing recursion

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Message-Id: <1424110807-15057-1-git-send-email-fweisbec@gmail.com>
Date:	Mon, 16 Feb 2015 19:20:07 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Huang Ying <ying.huang@...el.com>,
	Ingo Molnar <mingo@...nel.org>
Subject: [PATCH] sched: Fix preempt_schedule_common() triggering tracing recursion

Since the function graph tracer needs to disable preemption, it might
call preempt_schedule() after reenabling  it if something triggered the
need for rescheduling in between.

Therefore we can't trace preempt_schedule() itself because we would
face a function tracing recursion otherwise as the tracer is always
called before PREEMPT_ACTIVE gets set to prevent that recursion. This is
why preempt_schedule() is tagged as "notrace".

But the same issue applies to every function called by preempt_schedule()
before PREEMPT_ACTIVE is actually set. And preempt_schedule_common() is
one such example. Unfortunately we forgot to tag it as notrace as well
and as a result we are encountering tracing recursion since it got
introduced by a18b5d01819235629289212ad428a5ee2b40f0d9
	("sched: Fix missing preemption opportunity").

Let's fix that by applying the appropriate function tag to
preempt_schedule_common().

Reported-by: Huang Ying <ying.huang@...el.com>
Acked-by: Steven Rostedt <rostedt@...dmis.org>
Cc: Huang Ying <ying.huang@...el.com>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Steven Rostedt <rostedt@...dmis.org>
Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
---
 kernel/sched/core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 13049aa..683e850 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2899,7 +2899,7 @@ void __sched schedule_preempt_disabled(void)
 	preempt_disable();
 }
 
-static void preempt_schedule_common(void)
+static void __sched notrace preempt_schedule_common(void)
 {
 	do {
 		__preempt_count_add(PREEMPT_ACTIVE);
-- 
2.1.4

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