linux-kernel - [tip:sched/urgent] sched/fair: Fix the update of blocked load when newly idle

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Date:   Thu, 3 May 2018 02:25:28 -0700
From:   tip-bot for Vincent Guittot <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     mingo@...nel.org, hpa@...or.com, paulmck@...ux.vnet.ibm.com,
        hkallweit1@...il.com, linux-kernel@...r.kernel.org,
        tglx@...utronix.de, geert+renesas@...der.be,
        vincent.guittot@...aro.org, peterz@...radead.org,
        torvalds@...ux-foundation.org
Subject: [tip:sched/urgent] sched/fair: Fix the update of blocked load when
 newly idle

Commit-ID:  457be908c83637ee10bda085a23dc05afa3b14a0
Gitweb:     https://git.kernel.org/tip/457be908c83637ee10bda085a23dc05afa3b14a0
Author:     Vincent Guittot <vincent.guittot@...aro.org>
AuthorDate: Thu, 26 Apr 2018 12:19:32 +0200
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Thu, 3 May 2018 07:38:03 +0200

sched/fair: Fix the update of blocked load when newly idle

With commit:

  31e77c93e432 ("sched/fair: Update blocked load when newly idle")

... we release the rq->lock when updating blocked load of idle CPUs.

This opens a time window during which another CPU can add a task to this
CPU's cfs_rq.

The check for newly added task of idle_balance() is not in the common path.
Move the out label to include this check.

Reported-by: Heiner Kallweit <hkallweit1@...il.com>
Tested-by: Geert Uytterhoeven <geert+renesas@...der.be>
Signed-off-by: Vincent Guittot <vincent.guittot@...aro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Fixes: 31e77c93e432 ("sched/fair: Update blocked load when newly idle")
Link: http://lkml.kernel.org/r/20180426103133.GA6953@linaro.org
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 54dc31e7ab9b..e3002e5ada31 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -9847,6 +9847,7 @@ static int idle_balance(struct rq *this_rq, struct rq_flags *rf)
 	if (curr_cost > this_rq->max_idle_balance_cost)
 		this_rq->max_idle_balance_cost = curr_cost;
 
+out:
 	/*
 	 * While browsing the domains, we released the rq lock, a task could
 	 * have been enqueued in the meantime. Since we're not going idle,
@@ -9855,7 +9856,6 @@ static int idle_balance(struct rq *this_rq, struct rq_flags *rf)
 	if (this_rq->cfs.h_nr_running && !pulled_task)
 		pulled_task = 1;
 
-out:
 	/* Move the next balance forward */
 	if (time_after(this_rq->next_balance, next_balance))
 		this_rq->next_balance = next_balance;