linux-kernel - [PATCH 1/2] sched: Deny self-issued __set_cpus_allowed_ptr() when migrate

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Message-Id: <20201013140116.26651-1-valentin.schneider@arm.com>
Date:   Tue, 13 Oct 2020 15:01:15 +0100
From:   Valentin Schneider <valentin.schneider@....com>
To:     linux-kernel@...r.kernel.org
Cc:     tglx@...utronix.de, mingo@...nel.org, bigeasy@...utronix.de,
        qais.yousef@....com, swood@...hat.com, peterz@...radead.org,
        valentin.schneider@....com, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
        bristot@...hat.com, vincent.donnefort@....com, tj@...nel.org
Subject: [PATCH 1/2] sched: Deny self-issued __set_cpus_allowed_ptr() when migrate_disable()

  migrate_disable();
  set_cpus_allowed_ptr(current, {something excluding task_cpu(current)});
  affine_move_task(); <-- never returns

Signed-off-by: Valentin Schneider <valentin.schneider@....com>
---
 kernel/sched/core.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 4ccd1099adaa..7f4e38819de1 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2189,6 +2189,11 @@ static int __set_cpus_allowed_ptr(struct task_struct *p,
 	if (!(flags & SCA_MIGRATE_ENABLE) && cpumask_equal(&p->cpus_mask, new_mask))
 		goto out;
 
+	if (p == current &&
+	    is_migration_disabled(p) &&
+	    !cpumask_test_cpu(task_cpu(p), new_mask))
+		ret = -EBUSY;
+
 	/*
 	 * Picking a ~random cpu helps in cases where we are changing affinity
 	 * for groups of tasks (ie. cpuset), so that load balancing is not
-- 
2.27.0