[PATCH] sched: modify the comment about lock assumption in migrate_task_rq_fair()

[PATCH] sched: modify the comment about lock assumption in migrate_task_rq_fair()

[byungchul.park]

From: Byungchul Park <byungchul.park@lge.com>

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

Signed-off-by: Byungchul Park <byungchul.park@lge.com>
---
 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 077076f..6f43dfd 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5006,8 +5006,7 @@ 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, int next_cpu)
 {
-- 
1.7.9.5

[tip:sched/core] sched/fair: Modify the comment about lock assumptions in migrate_task_rq_fair()

[tip-bot for Byungchul Park]

Commit-ID:  525628c73bd6af65f27d927e699e7460d7d55ed3
Gitweb:     http://git.kernel.org/tip/525628c73bd6af65f27d927e699e7460d7d55ed3
Author:     Byungchul Park <byungchul.park@lge.com>
AuthorDate: Wed, 18 Nov 2015 09:34:59 +0900
Committer:  Ingo Molnar <mingo@kernel.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@lge.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1447806899-20303-1-git-send-email-byungchul.park@lge.com
Signed-off-by: Ingo Molnar <mingo@kernel.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)
 {