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Subject[PATCH v4 18/19] sched: Deny self-issued __set_cpus_allowed_ptr() when migrate_disable()
From: Valentin Schneider <valentin.schneider@arm.com>

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

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

--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2182,8 +2182,17 @@ static int __set_cpus_allowed_ptr(struct
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

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