linux-kernel - [tip:sched/core] sched/fair: Modify the comment about lock assumptions in migrate_task_rq

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Message-ID: <tip-525628c73bd6af65f27d927e699e7460d7d55ed3@git.kernel.org>
Date:	Mon, 23 Nov 2015 08:24:11 -0800
From:	tip-bot for Byungchul Park <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	hpa@...or.com, mingo@...nel.org, efault@....de, tglx@...utronix.de,
	torvalds@...ux-foundation.org, linux-kernel@...r.kernel.org,
	peterz@...radead.org, byungchul.park@....com
Subject: [tip:sched/core] sched/fair:
  Modify the comment about lock assumptions in migrate_task_rq_fair()

Commit-ID:  525628c73bd6af65f27d927e699e7460d7d55ed3
Gitweb:     http://git.kernel.org/tip/525628c73bd6af65f27d927e699e7460d7d55ed3
Author:     Byungchul Park <byungchul.park@....com>
AuthorDate: Wed, 18 Nov 2015 09:34:59 +0900
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Mon, 23 Nov 2015 09:48:20 +0100

sched/fair: Modify the comment about lock assumptions in migrate_task_rq_fair()

The comment describing migrate_task_rq_fair() says that the caller
should hold p->pi_lock. But in some cases the caller can hold
task_rq(p)->lock instead of p->pi_lock. So the comment is broken and
this patch fixes it.

Signed-off-by: Byungchul Park <byungchul.park@....com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Mike Galbraith <efault@....de>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Link: http://lkml.kernel.org/r/1447806899-20303-1-git-send-email-byungchul.park@lge.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 kernel/sched/fair.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index f7017ad..ff8ec86 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5058,8 +5058,7 @@ select_task_rq_fair(struct task_struct *p, int prev_cpu, int sd_flag, int wake_f
 /*
  * Called immediately before a task is migrated to a new cpu; task_cpu(p) and
  * cfs_rq_of(p) references at time of call are still valid and identify the
- * previous cpu.  However, the caller only guarantees p->pi_lock is held; no
- * other assumptions, including the state of rq->lock, should be made.
+ * previous cpu. The caller guarantees p->pi_lock or task_rq(p)->lock is held.
  */
 static void migrate_task_rq_fair(struct task_struct *p)
 {
--
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