linux-kernel - [PATCH] sched_fair: test list head instead of list entry in throttle_cfs

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Date:	Wed, 24 Jun 2015 12:41:47 -0700
From:	Cong Wang <xiyou.wangcong@...il.com>
To:	linux-kernel@...r.kernel.org
Cc:	Cong Wang <xiyou.wangcong@...il.com>,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Cong Wang <cwang@...pensource.com>
Subject: [PATCH] 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.

Cc: Ingo Molnar <mingo@...hat.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Signed-off-by: Cong Wang <xiyou.wangcong@...il.com>
Signed-off-by: Cong Wang <cwang@...pensource.com>
---
 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 40a7fcb..ee91917 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
-- 
1.8.3.1

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