Re: [PATCH] Revert "cifs: remove all cifs files before kill super"

[Namjae Jeon]

On Tue, Aug 18, 2026 at 12:13 PM Zizhi Wo <wozizhi@xxxxxxxxxxxxxxx> wrote:
>
> From: Zizhi Wo <wozizhi@xxxxxxxxxx>
>
> This reverts commit 6d9a4aaaa8b2612b5ef9d581e2f286a458b71ee1.
>
> First, directly flushing fileinfo_put_wq in that commit cannot guarantee
> that all in-flight I/O has run its cleanup_work on system_dfl_wq and
> subsequently called queue_work(fileinfo_put_wq, ...). Flushing only the
> latter workqueue may therefore miss puts that have not yet been queued, so
> the fix is not reliable in the first place. Moreover, this fix flushes
> inside cifs_umount(), which means the busy-dentry warning can still be
> triggered when umount_check() is called inside kill_anon_super(), because
> kill_anon_super() is executed before cifs_umount().
>
> Second, commit 75f5c412fa86 ("smb: client: fix busy dentry warning on
> unmount after DIO") already drains both serverclose_wq and fileinfo_put_wq
> in cifs_kill_sb(), before kill_anon_super(). By adding a per-superblock
> outstanding-rreq counter, it guarantees that all cleanup_work for this sb
> have run, and thus all relevant cfile puts are queued on fileinfo_put_wq
> or serverclose_wq.
>
> Third, no path between those drains and cifs_umount() can queue new work
> onto either workqueue. In the "cifs_sb->root == NULL" path there are no
> file-related workers either, so that case is safe as well.
>
> Therefore the busy-dentry and null-ptr-deref problems cannot arise, and
> the flush added by commit 6d9a4aaaa8b2 ("cifs: remove all cifs files before
> kill super") is redundant and can be removed.
>
> Signed-off-by: Zizhi Wo <wozizhi@xxxxxxxxxx>
Will apply it to #for-next.
Thanks!