6.12-stable review patch. If anyone has any objections, please let me know.
------------------
From: Josh Don <joshdon@xxxxxxxxxx>
[ 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@xxxxxxxxxx>
Acked-and-tested-by: Vincent Guittot <vincent.guittot@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Acked-by: Waiman Long <longman@xxxxxxxxxx>
Tested-by: Madadi Vineeth Reddy <vineethr@xxxxxxxxxxxxx>
Link: https://lkml.kernel.org/r/20241111182738.1832953-1-joshdon@xxxxxxxxxx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
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);
--
2.43.0
