ceph: fix leaked inode ref due to snap metadata writeback race

We create a ceph_cap_snap if there is dirty cap metadata (for writeback to
mds) OR dirty pages (for writeback to osd).  It is thus possible that the
metadata has been written back to the MDS but the OSD data has not when
the cap_snap is created.  This results in a cap_snap with dirty(caps) == 0.
The problem is that cap writeback to the MDS isn't necessary, and a
FLUSHSNAP cap op gets no ack from the MDS.  This leaves the cap_snap
attached to the inode along with its inode reference.

Fix the problem by dropping the cap_snap if it becomes 'complete' (all
pages written out) and dirty(caps) == 0 in ceph_put_wrbuffer_cap_refs().

Also, BUG() in __ceph_flush_snaps() if we encounter a cap_snap with
dirty(caps) == 0.

Signed-off-by: Sage Weil <sage@newdream.net>

1 files changed, 6 insertions, 4 deletions

diff --git a/fs/ceph/snap.c b/fs/ceph/snap.c
index df04e210a055..7e3e5f9edaa4 100644
--- a/fs/ceph/snap.c
+++ b/fs/ceph/snap.c
@@ -521,15 +521,17 @@ int __ceph_finish_cap_snap(struct ceph_inode_info *ci,
         capsnap->ctime = inode->i_ctime;
         capsnap->time_warp_seq = ci->i_time_warp_seq;
         if (capsnap->dirty_pages) {
-                dout("finish_cap_snap %p cap_snap %p snapc %p %llu s=%llu "
+                dout("finish_cap_snap %p cap_snap %p snapc %p %llu %s s=%llu "
                      "still has %d dirty pages\n", inode, capsnap,
                      capsnap->context, capsnap->context->seq,
-                     capsnap->size, capsnap->dirty_pages);
+                     ceph_cap_string(capsnap->dirty), capsnap->size,
+                     capsnap->dirty_pages);
                 return 0;
         }
-        dout("finish_cap_snap %p cap_snap %p snapc %p %llu s=%llu clean\n",
+        dout("finish_cap_snap %p cap_snap %p snapc %p %llu %s s=%llu\n",
              inode, capsnap, capsnap->context,
-             capsnap->context->seq, capsnap->size);
+             capsnap->context->seq, ceph_cap_string(capsnap->dirty),
+             capsnap->size);
 
         spin_lock(&mdsc->snap_flush_lock);
         list_add_tail(&ci->i_snap_flush_item, &mdsc->snap_flush_list);