Re: [PATCH 1/3] cgroup/cpuset: Fix deadline bandwidth leak in cpuset_can_attach()

[Waiman Long <longman@redhat.com>]

On 5/9/26 12:48 PM, Aaron Tomlin wrote:
> During a cgroup migration, cpuset_can_attach() iterates over the
> provided taskset. If a task within the batch is a deadline (DL) task,
> the destination cpuset's DL metrics (i.e., nr_migrate_dl_tasks and
> sum_migrate_dl_bw) are appropriately incremented.
>
> However, if a subsequent task in the same migration batch fails the
> task_can_attach() check, the loop aborts and jumps directly to
> out_unlock. Consequently, any DL metrics accumulated from previously
> processed tasks in the batch remain permanently inflated in the
> destination cpuset. Because the migration is subsequently aborted by the
> cgroup core, cpuset_cancel_attach() is never invoked to unwind these
> specific increments.
>
> This behaviour results in a permanent leak of deadline bandwidth, which
> incorrectly restricts the admission control capacity of the destination
> cpuset.
>
> To resolve this, introduce an out_unlock_reset failure path that
> conditionally invokes reset_migrate_dl_data(). This guarantees that if a
> batch migration is aborted for any reason, the pending DL metrics are
> safely reset before returning the error.
>
> Fixes: 0a67b847e1f06 ("cpuset: Allow setscheduler regardless of manipulated task")

That is not the commit that introduced the bug. Anyway, there is already 
another patch sent recently to fix this bug. See

https://lore.kernel.org/lkml/20260509102031.97608-2-zhangguopeng@kylinos.cn/

Cheers,
Longman