Re: [PATCH v3] md: clear MD_CLOSING when array_state_store() bails on interrupted lock

[Jinpu Wang]

On Fri, Nov 6, 2026 at 2:42 AM yu kuai <yukuai@xxxxxxx> wrote:
>
> Hi,
>
> 在 2026/11/2 15:35, Jack Wang 写道:
> > From: Jack Wang <jinpu.wang@xxxxxxxxxxxxxxx>
> >
> > Writing "clear", "readonly", "inactive" or "read_auto" to array_state
> > calls mddev_set_closing_and_sync_blockdev(), which sets MD_CLOSING to
> > keep the array from being reopened while it is torn down. The flag is
> > only cleared again at the tail of array_state_store() (for readonly /
> > read_auto / inactive, or the failed-clear case).
> >
> > Between setting the flag and reaching that tail there is an early return:
> >
> >       err = mddev_lock(mddev);
> >       if (err)
> >               return err;
> >
> > mddev_lock() is mutex_lock_interruptible() on reconfig_mutex. If the
> > writing task catches a signal while blocked there, it returns -EINTR and
> > MD_CLOSING is left set on a still-running array. do_md_stop() /
> > md_set_readonly() never ran, so the array keeps working internally, but
> > every subsequent md_open() now returns -ENODEV for all callers - the
> > device shows up in /proc/mdstat and sysfs is fully populated, yet cannot
> > be opened, and cannot be recovered without a reboot (all clear paths
> > either need the device open or re-enter test_and_set_bit(MD_CLOSING) and
> > bail with -EBUSY before the clear).
> >
> > The window is easy to hit on a busy host: reconfig_mutex is held for long
> > stretches by a running resync/recovery, widening the interruptible wait,
> > and a userspace helper writing to array_state and then being killed or
> > timed out is enough to leak the flag.
> >
> > Clear the flag directly in the interrupted-lock exit. Guard the clear
> > with a set_closing flag that records whether this write actually set
> > MD_CLOSING: the set call is skipped when the array is not running
> > read-write (or mddev->pers is NULL), and in that case this write must
> > not clear a MD_CLOSING it never set. This also tightens the pre-existing
> > tail clear, which had the same unconditional behaviour.
> >
> > Fixes: 99b902ac1725 ("md: sync blockdev before stopping raid or setting readonly")
> > Assisted-by: Claude:claude-opus-4-8 [Claude Code]
>
> checkpatch reprot error with this tag.
ok, will drop it.
>
> > Signed-off-by: Jack Wang <jinpu.wang@xxxxxxxxxxxxxxx>
> > ---
> > v3: (Kuai) clear MD_CLOSING directly at the mddev_lock() failure and
> >      return, drop the out_clear_closing label; reword the commit message.
> >      Keep the set_closing guard: the set call is skipped when the array
> >      is not rdwr or mddev->pers is NULL, so this write may not own the
> >      flag. Rebased on v7.4-rc1.
> > v2: guard the clear with set_closing.
> >
> >   drivers/md/md.c | 13 ++++++++++---
> >   1 file changed, 10 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/md/md.c b/drivers/md/md.c
> > index 03e35386a802..f14a31387990 100644
> > --- a/drivers/md/md.c
> > +++ b/drivers/md/md.c
> > @@ -4671,6 +4671,7 @@ array_state_store(struct mddev *mddev, const char *buf, size_t len)
> >   {
> >       int err = 0;
> >       enum array_state st = match_word(buf, array_states);
> > +     bool set_closing = false;
> >
> >       /* No lock dependent actions */
> >       switch (st) {
> > @@ -4691,6 +4692,7 @@ array_state_store(struct mddev *mddev, const char *buf, size_t len)
> >               err = mddev_set_closing_and_sync_blockdev(mddev, 0);
> >               if (err)
> >                       return err;
> > +             set_closing = true;
> >               break;
> >       default:
> >               break;
> > @@ -4718,8 +4720,12 @@ array_state_store(struct mddev *mddev, const char *buf, size_t len)
> >               return err ?: len;
> >       }
> >       err = mddev_lock(mddev);
> > -     if (err)
> > +     if (err) {
> > +             /* Interrupted before any teardown ran, don't leak MD_CLOSING */
> > +             if (set_closing)
> > +                     clear_bit(MD_CLOSING, &mddev->flags);
> >               return err;
> > +     }
> >
> >       switch (st) {
> >       case inactive:
> > @@ -4792,8 +4798,9 @@ array_state_store(struct mddev *mddev, const char *buf, size_t len)
> >       }
> >       mddev_unlock(mddev);
> >
> > -     if (st == readonly || st == read_auto || st == inactive ||
> > -         (err && st == clear))
> > +     if (set_closing &&
> > +         (st == readonly || st == read_auto || st == inactive ||
> > +          (err && st == clear)))
>
> Just keep the checking of set_closing should be enough.

A bare "if (set_closing)" at the tail would also clear MD_CLOSING after a
successful "clear". do_md_stop() -> md_clean() keeps it on purpose so the
stopped array can't be reopened (except legacy mode with hold_active).

So v4 uses:

        if (set_closing && (st != clear || err))

i.e. always clear for readonly/read_auto/inactive, and for "clear" only
if it failed (array still live). Does that look OK to you?

--
Thanks,
>
> >               clear_bit(MD_CLOSING, &mddev->flags);
> >
> >       return err ?: len;
>
> --
> Thanks,
> Kuai