From 464c3733786db6813e4b161e1ae56e00a1472ff4 Mon Sep 17 00:00:00 2001
From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Date: Thu, 26 Aug 2021 15:37:38 +0200
Subject: [PATCH 299/327] sched: Fix get_push_task() vs migrate_disable()

push_rt_task() attempts to move the currently running task away if the
next runnable task has migration disabled and therefore is pinned on the
current CPU.

The current task is retrieved via get_push_task() which only checks for
nr_cpus_allowed == 1, but does not check whether the task has migration
disabled and therefore cannot be moved either. The consequence is a
pointless invocation of the migration thread which correctly observes
that the task cannot be moved.

Return NULL if the task has migration disabled and cannot be moved to
another CPU.

Cc: stable-rt@vger.kernel.org
Fixes: a7c81556ec4d3 ("sched: Fix migrate_disable() vs rt/dl balancing")
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20210826133738.yiotqbtdaxzjsnfj@linutronix.de
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
 kernel/sched/sched.h | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index f0fc599cf79c..0e3b8e19e721 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1949,6 +1949,9 @@ static inline struct task_struct *get_push_task(struct rq *rq)
 	if (p->nr_cpus_allowed == 1)
 		return NULL;
 
+	if (p->migration_disabled)
+		return NULL;
+
 	rq->push_busy = true;
 	return get_task_struct(p);
 }
-- 
2.49.0

