Re: [PATCH v2] ceph: fix leaked inode reference on writeback abort at umount

Hi Matthew,

LGTM.

Reviewed-by: Xiubo Li <[email protected]>

Thanks
- Xiubo

On Wed, 12 Aug 2026 at 10:13, Matthew Brown <[email protected]> wrote:
>
> ceph_dirty_folio() takes a wrbuffer claim on each newly dirtied folio: it
> bumps i_wrbuffer_ref (taking an ihold() on the 0->1 transition) and
> attaches the snap_context to folio->private.  That claim is released only
> by ceph_put_wrbuffer_cap_refs(), which for a submitted write runs from
> writepages_finish().
>
> In ceph_submit_write(), if ceph_inc_osd_stopping_blocker() fails -- which
> happens during umount -- the request is aborted before submission: the
> already-collected folios are only redirtied and unlocked, so
> writepages_finish() never runs and the claim is leaked.
> redirty_page_for_writepage() -> folio_redirty_for_writepage() ->
> filemap_dirty_folio() sets PG_dirty directly and does not go through
> ->dirty_folio, so ceph_dirty_folio() is not re-entered to rebalance it.
> Because every subsequent writeback also fails the osd_stopping_blocker,
> i_wrbuffer_ref never returns to 0, the ihold() is never dropped, and the
> inode cannot be evicted:
>
>   VFS: Busy inodes after unmount of ceph
>   kernel BUG at fs/super.c:650!
>
> Release the orphaned claim in the abort path before redirtying, via
> ceph_undo_wrbuffer_claim(): detach the snap_context, drop the wrbuffer
> reference (letting i_wrbuffer_ref reach 0 and iput() the inode), and drop
> the snap_context reference -- i.e. do what writepages_finish() would have
> done for these never-submitted folios.
>
> Only the locked_pages entries are undone; folios still in the fbatch were
> never dirty-cleared by this call (folio_clear_dirty_for_io() is the
> ownership-transfer point, and a successful move NULLs the fbatch slot), so
> they hold no claim this call owns.
>
> Fixes: fd7449d937e7 ("ceph: fix generic/421 test failure")
> Signed-off-by: Matthew Brown <[email protected]>
> ---
>
> v2:
>  - Reword the commit message: the leak is an orphaned wrbuffer claim on an
>    unsubmitted write (writepages_finish() never runs), not
>    redirty_page_for_writepage() re-entering ceph_dirty_folio().  Thanks to
>    Alex Markuze for the correction.
>  - Convert ceph_undo_wrbuffer_claim() to the folio API
>    (struct folio * / folio_detach_private()), per Alex Markuze.
>  - Spell out the locked_pages/fbatch ownership split in the message, per
>    Xiubo Li's comment.
>
> v1: https://lore.kernel.org/all/[email protected]/
>  fs/ceph/addr.c | 11 +++++++++++
>  1 file changed, 11 insertions(+)
>
> diff --git a/fs/ceph/addr.c b/fs/ceph/addr.c
> index ecf33b6..e9f561b 100644
> --- a/fs/ceph/addr.c
> +++ b/fs/ceph/addr.c
> @@ -1426,6 +1426,16 @@ void ceph_shift_unused_folios_left(struct folio_batch *fbatch)
>         fbatch->nr = n;
>  }
>
> +static void ceph_undo_wrbuffer_claim(struct inode *inode, struct folio *folio)
> +{
> +       struct ceph_snap_context *snapc = folio_detach_private(folio);
> +
> +       if (!snapc)
> +               return;
> +       ceph_put_wrbuffer_cap_refs(ceph_inode(inode), 1, snapc);
> +       ceph_put_snap_context(snapc);
> +}
> +
>  static
>  int ceph_submit_write(struct address_space *mapping,
>                         struct writeback_control *wbc,
> @@ -1489,6 +1499,7 @@ int ceph_submit_write(struct address_space *mapping,
>                         if (!page)
>                                 continue;
>
> +                       ceph_undo_wrbuffer_claim(inode, page_folio(page));
>                         redirty_page_for_writepage(wbc, page);
>                         unlock_page(page);
>                 }
> --
> 2.44.0
>