Re: [PATCH v2] cgroup/cpuset: Fix update_prstate() always returning 0 on partition errors

[Michal Koutný]

Hi.

On Tue, Jun 02, 2026 at 12:55:21PM +0800, Tao Cui <cui.tao@xxxxxxxxx> wrote:
> update_prstate() stores the error code in cs->prs_err and transitions
> the partition to an invalid state, but always returns 0. The caller
> cpuset_partition_write() uses "return retval ?: nbytes", so the write
> syscall always appears to succeed from userspace even when the partition
> became invalid.
> Return -EINVAL when err is set so userspace can detect
> the failure immediately.

This is quite a visible UAPI change (a write can succeed to invalidate a
partition) and users are meant to watch for cpuset.cpus.partition state
anyway for asynchronous changes.

I'd not change this gratuitously.

Michal

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