linux-kernel - [PATCH] sched/core: Fix a missed update of user_cpus

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Message-Id: <20230203181849.221943-1-longman@redhat.com>
Date:   Fri,  3 Feb 2023 13:18:49 -0500
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>,
        Will Deacon <will@...nel.org>
Cc:     Phil Auld <pauld@...hat.com>, Tejun Heo <tj@...nel.org>,
        linux-kernel@...r.kernel.org, Waiman Long <longman@...hat.com>
Subject: [PATCH] sched/core: Fix a missed update of user_cpus_ptr

Since commit 8f9ea86fdf99 ("sched: Always preserve the user requested
cpumask"), a successful call to sched_setaffinity() should always save
the user requested cpu affinity mask in a task's user_cpus_ptr. However,
when the given cpu mask is the same as the current one, user_cpus_ptr
is not updated. Fix this by saving the user mask in this case too.

Fixes: 8f9ea86fdf99 ("sched: Always preserve the user requested cpumask")
Signed-off-by: Waiman Long <longman@...hat.com>
---
 kernel/sched/core.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 30d9752e2ca5..91255f791df3 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2951,8 +2951,11 @@ static int __set_cpus_allowed_ptr_locked(struct task_struct *p,
 	}
 
 	if (!(ctx->flags & SCA_MIGRATE_ENABLE)) {
-		if (cpumask_equal(&p->cpus_mask, ctx->new_mask))
+		if (cpumask_equal(&p->cpus_mask, ctx->new_mask)) {
+			if (ctx->flags & SCA_USER)
+				swap(p->user_cpus_ptr, ctx->user_mask);
 			goto out;
+		}
 
 		if (WARN_ON_ONCE(p == current &&
 				 is_migration_disabled(p) &&
-- 
2.31.1