linux-kernel - [tip:sched/core] sched: Fix preempt_schedule

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Date:	Wed, 18 Feb 2015 09:06:39 -0800
From:	tip-bot for Frederic Weisbecker <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	peterz@...radead.org, hpa@...or.com, tglx@...utronix.de,
	torvalds@...ux-foundation.org, mingo@...nel.org,
	linux-kernel@...r.kernel.org, rostedt@...dmis.org,
	ying.huang@...el.com, fweisbec@...il.com
Subject: [tip:sched/core] sched: Fix preempt_schedule_common()
  triggering tracing recursion

Commit-ID:  06b1f8083d6ed379ec1207a96339f23e8f7abfcf
Gitweb:     http://git.kernel.org/tip/06b1f8083d6ed379ec1207a96339f23e8f7abfcf
Author:     Frederic Weisbecker <fweisbec@...il.com>
AuthorDate: Mon, 16 Feb 2015 19:20:07 +0100
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Wed, 18 Feb 2015 14:27:38 +0100

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:

   a18b5d0181923 ("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>
Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Acked-by: Steven Rostedt <rostedt@...dmis.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Link: http://lkml.kernel.org/r/1424110807-15057-1-git-send-email-fweisbec@gmail.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 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 f77acd9..c314000 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2839,7 +2839,7 @@ 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);
--
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