ceph: fix leaked inode reference on writeback abort at umount

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.

Cc: stable@vger.kernel.org
Fixes: fd7449d937e7 ("ceph: fix generic/421 test failure")
Signed-off-by: Matthew Brown <matthew@bargrove.com>
Reviewed-by: Xiubo Li <xiubo.li@clyso.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

diff --git a/fs/ceph/addr.c b/fs/ceph/addr.c
index 7e454b8..657c2cb 100644 (file)
--- a/fs/ceph/addr.c
+++ b/fs/ceph/addr.c
@@ -1429,6 +1429,16 @@ 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,
@@ -1492,6 +1502,7 @@ new_request:
                        if (!page)
                                continue;
 
+                       ceph_undo_wrbuffer_claim(inode, page_folio(page));
                        redirty_page_for_writepage(wbc, page);
                        unlock_page(page);
                }