6.12-stable review patch. If anyone has any objections, please let me know.
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From: Josh Don joshdon@google.com
[ Upstream commit 70ee7947a29029736a1a06c73a48ff37674a851b ]
Commit 8f9ea86fdf99b 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: 8f9ea86fdf99b ("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 Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/sched/syscalls.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/sched/syscalls.c b/kernel/sched/syscalls.c index 24f9f90b6574e..1784ed1fb3fe5 100644 --- a/kernel/sched/syscalls.c +++ b/kernel/sched/syscalls.c @@ -1238,7 +1238,7 @@ 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);