linux-kernel - [PATCH v9 7/7] sched: Always clear user_cpus_ptr in do_set_cpus

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Date:   Fri, 16 Sep 2022 14:32:17 -0400
From:   Waiman Long <longman@...hat.com>
To:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Valentin Schneider <vschneid@...hat.com>,
        Tejun Heo <tj@...nel.org>, Zefan Li <lizefan.x@...edance.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Will Deacon <will@...nel.org>
Cc:     linux-kernel@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Waiman Long <longman@...hat.com>
Subject: [PATCH v9 7/7] sched: Always clear user_cpus_ptr in do_set_cpus_allowed()

The do_set_cpus_allowed() function is used by either kthread_bind() or
select_fallback_rq(). In both cases the user affinity (if any) should be
destroyed too.

Suggested-by: Peter Zijlstra <peterz@...radead.org>
Signed-off-by: Waiman Long <longman@...hat.com>
---
 kernel/sched/core.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index ce626cad4105..a5240c603667 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2599,14 +2599,20 @@ __do_set_cpus_allowed(struct task_struct *p, struct affinity_context *ctx)
 		set_next_task(rq, p);
 }
 
+/*
+ * Used for kthread_bind() and select_fallback_rq(), in both cases the user
+ * affinity (if any) should be destroyed too.
+ */
 void do_set_cpus_allowed(struct task_struct *p, const struct cpumask *new_mask)
 {
 	struct affinity_context ac = {
 		.new_mask  = new_mask,
-		.flags     = 0,
+		.user_mask = NULL,
+		.flags     = SCA_USER,	/* clear the user requested mask */
 	};
 
 	__do_set_cpus_allowed(p, &ac);
+	kfree(ac.user_mask);
 }
 
 int dup_user_cpus_ptr(struct task_struct *dst, struct task_struct *src,
-- 
2.31.1