From: Kevin Hilman <khilman@linaro.org>
Date: Wed, 8 Apr 2015 21:32:07 +0000 (-0700)
Subject: sched: hmp: fix spinlock recursion in active migration
X-Git-Tag: firefly_0821_release~3680^2~16^2^2
X-Git-Url: http://plrg.eecs.uci.edu/git/?a=commitdiff_plain;ds=sidebyside;h=c1f0c1f51bf7b9111de27c3cdbea9b647351bf7b;p=firefly-linux-kernel-4.4.55.git

sched: hmp: fix spinlock recursion in active migration

Commit cd5c2cc93d3d (hmp: Remove potential for task_struct access
race) introduced a put_task_struct() to prevent races, but in doing so
introduced potential spinlock recursion.  (This change was further
consolidated in commit 0baa5811bacf -- sched: hmp: unify active
migration code.)

Unfortunately, the put_task_struct() is done while the runqueue
spinlock is held, but put_task_struct() can also cause a reschedule
causing the runqueue lock to be acquired recursively.

To fix, move the put_task_struct() outside the runqueue spinlock.

Reported-by: Victor Lixin <victor.lixin@hisilicon.com>
Cc: Jorge Ramirez-Ortiz <jorge.ramirez-ortiz@linaro.org>
Cc: Liviu Dudau <Liviu.Dudau@arm.com>
Signed-off-by: Kevin Hilman <khilman@linaro.org>
Reviewed-by: Jon Medhurst <tixy@linaro.org>
Reviewed-by: Alex Shi <alex.shi@linaro.org>
Reviewed-by: Chris Redpath <chris.redpath@arm.com>
Signed-off-by: Jon Medhurst <tixy@linaro.org>
---

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index fd57f0be5b4e..22ce83eb73f8 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6462,10 +6462,10 @@ static int __do_active_load_balance_cpu_stop(void *data, bool check_sd_lb_flag)
 	rcu_read_unlock();
 	double_unlock_balance(busiest_rq, target_rq);
 out_unlock:
-	if (!check_sd_lb_flag)
-		put_task_struct(p);
 	busiest_rq->active_balance = 0;
 	raw_spin_unlock_irq(&busiest_rq->lock);
+	if (!check_sd_lb_flag)
+		put_task_struct(p);
 	return 0;
 }