Re: [PATCH v4 1/2] f2fs: avoid NULL checkpoint thread access in sysfs

[Chao Yu]

On 8/4/26 09:48, Wenjie Qi wrote:
> checkpoint_merge can be enabled even when no checkpoint merge thread is
> running. A read-only mount is one case: f2fs does not start
> f2fs_issue_ckpt there, but ckpt_thread_ioprio is still writable through
> sysfs.
>
> The ckpt_thread_ioprio store path updates the saved ioprio value and,
> when checkpoint_merge is enabled, calls set_task_ioprio() for the
> checkpoint thread. If cprc->f2fs_issue_ckpt is NULL, that dereferences a
> NULL task pointer.
>
> Protect ckpt_thread_ioprio sysfs writes with s_umount as well, so the
> checkpoint thread cannot disappear under the store path while updating
> its ioprio.
>
> Fixes: e65920661708 ("f2fs: add ckpt_thread_ioprio sysfs node")
> Cc: stable@xxxxxxxxxx
> Signed-off-by: Wenjie Qi <qiwenjie@xxxxxxxxxx>

Reviewed-by: Chao Yu <chao@xxxxxxxxxx>

Thanks,