linux-kernel - [tip:sched/core] sched/fair: Test list head instead of list entry in throttle_cfs

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Message-ID: <tip-d49db342f0e276b354383b3281c5668b6b80f5c2@git.kernel.org>
Date:	Mon, 6 Jul 2015 08:35:39 -0700
From:	tip-bot for Cong Wang <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	hpa@...or.com, xiyou.wangcong@...il.com, tglx@...utronix.de,
	torvalds@...ux-foundation.org, bsegall@...gle.com,
	linux-kernel@...r.kernel.org, peterz@...radead.org,
	cwang@...pensource.com, mingo@...nel.org
Subject: [tip:sched/core] sched/fair:
  Test list head instead of list entry in throttle_cfs_rq()

Commit-ID:  d49db342f0e276b354383b3281c5668b6b80f5c2
Gitweb:     http://git.kernel.org/tip/d49db342f0e276b354383b3281c5668b6b80f5c2
Author:     Cong Wang <xiyou.wangcong@...il.com>
AuthorDate: Wed, 24 Jun 2015 12:41:47 -0700
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Mon, 6 Jul 2015 14:15:08 +0200

sched/fair: Test list head instead of list entry in throttle_cfs_rq()

According to the comments, we need to test if this is
the first throttled task, however, list_empty() tests on
the entry cfs_rq->throttled_list, not the head, this is wrong.

This is a bug because we don't re-init the list entry after
removing it from the list, so list_empty() could return false
even if the list is really empty.

Signed-off-by: Cong Wang <xiyou.wangcong@...il.com>
Signed-off-by: Cong Wang <cwang@...pensource.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Reviewed-by: Ben Segall <bsegall@...gle.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Link: http://lkml.kernel.org/r/1435174907-432-1-git-send-email-xiyou.wangcong@gmail.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 kernel/sched/fair.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 65c8f3e..d113c3b 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3683,7 +3683,7 @@ static void throttle_cfs_rq(struct cfs_rq *cfs_rq)
 	cfs_rq->throttled = 1;
 	cfs_rq->throttled_clock = rq_clock(rq);
 	raw_spin_lock(&cfs_b->lock);
-	empty = list_empty(&cfs_rq->throttled_list);
+	empty = list_empty(&cfs_b->throttled_cfs_rq);
 
 	/*
 	 * Add to the _head_ of the list, so that an already-started
--
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