[tip: sched/core] sched: Deny self-issued __set_cpus_allowed_ptr() when migrate_disable()

[tip-bot2 for Valentin Schneider]

The following commit has been merged into the sched/core branch of tip:

Commit-ID:     885b3ba47aa5cc16550beb8a42181ad5e8302ceb
Gitweb:        https://git.kernel.org/tip/885b3ba47aa5cc16550beb8a42181ad5e8302ceb
Author:        Valentin Schneider <valentin.schneider@xxxxxxx>
AuthorDate:    Tue, 13 Oct 2020 15:01:15 +01:00
Committer:     Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Tue, 10 Nov 2020 18:39:02 +01:00

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@xxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Link: https://lkml.kernel.org/r/20201013140116.26651-1-valentin.schneider@xxxxxxx
---
 kernel/sched/core.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index e92d785..88c6fcb 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2238,8 +2238,17 @@ static int __set_cpus_allowed_ptr(struct task_struct *p,
 		goto out;
 	}
 
-	if (!(flags & SCA_MIGRATE_ENABLE) && cpumask_equal(&p->cpus_mask, new_mask))
-		goto out;
+	if (!(flags & SCA_MIGRATE_ENABLE)) {
+		if (cpumask_equal(&p->cpus_mask, new_mask))
+			goto out;
+
+		if (WARN_ON_ONCE(p == current &&
+				 is_migration_disabled(p) &&
+				 !cpumask_test_cpu(task_cpu(p), new_mask))) {
+			ret = -EBUSY;
+			goto out;
+		}
+	}
 
 	/*
 	 * Picking a ~random cpu helps in cases where we are changing affinity