sched: hmp: fix spinlock recursion in active migration

[original commit message]
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
onsolidated 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.

[additional commit message by Chanwoo Choi]
We did not apply hmp patch[1] because patch[1] clean the code by sharing the
same code. When I applied hmp patch[1], scheduling problem issue occured.
[1] commit 0baa5811bacf -- sched: hmp: unify active migration code.)
So, this patch move the put_task_struct() just 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>
[cw00.choi: Fix the merge conflict]
Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>

1 files changed, 2 insertions, 2 deletions

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 5900db7e1fba..55b42fc00294 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -9160,9 +9160,9 @@ static int hmp_active_task_migration_cpu_stop(void *data)
 	rcu_read_unlock();
 	double_unlock_balance(busiest_rq, target_rq);
 out_unlock:
-	put_task_struct(p);
 	busiest_rq->active_balance = 0;
 	raw_spin_unlock_irq(&busiest_rq->lock);
+	put_task_struct(p);
 	return 0;
 }
 
@@ -9234,9 +9234,9 @@ static int hmp_idle_pull_cpu_stop(void *data)
 	rcu_read_unlock();
 	double_unlock_balance(busiest_rq, target_rq);
 out_unlock:
-	put_task_struct(p);
 	busiest_rq->active_balance = 0;
 	raw_spin_unlock_irq(&busiest_rq->lock);
+	put_task_struct(p);
 	return 0;
 }