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sched: fix warning in sched_setaffinity

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Commit 8f9ea86fdf added some logic to sched_setaffinity that included
a WARN when a per-task affinity assignment races with a cpuset update.

Specifically, we can have a race where a cpuset update results in the
task affinity no longer being a subset of the cpuset. That's fine; we
have a fallback to instead use the cpuset mask. However, we have a WARN
set up that will trigger if the cpuset mask has no overlap at all with
the requested task affinity. This shouldn't be a warning condition; its
trivial to create this condition.

Reproduced the warning by the following setup:

- $PID inside a cpuset cgroup
- another thread repeatedly switching the cpuset cpus from 1-2 to just 1
- another thread repeatedly setting the $PID affinity (via taskset) to 2

Fixes: 8f9ea86fdf ("sched: Always preserve the user requested cpumask")
Signed-off-by: Josh Don <joshdon@google.com>
Acked-and-tested-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Waiman Long <longman@redhat.com>
Tested-by: Madadi Vineeth Reddy <vineethr@linux.ibm.com>
Link: https://lkml.kernel.org/r/20241111182738.1832953-1-joshdon@google.com
This commit is contained in:
Josh Don 2024-11-11 10:27:38 -08:00 committed by Peter Zijlstra
parent 22368fe1f9
commit 70ee7947a2
1 changed files with 1 additions and 1 deletions
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2
kernel/sched/syscalls.c
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@ -1200,7 +1200,7 @@ int __sched_setaffinity(struct task_struct *p, struct affinity_context *ctx)
bool empty = !cpumask_and(new_mask, new_mask,
ctx->user_mask);
if (WARN_ON_ONCE(empty))
if (empty)
cpumask_copy(new_mask, cpus_allowed);
}
__set_cpus_allowed_ptr(p, ctx);