ceph: maintain i_head_snapc when any caps are dirty, not just for data

We used to use i_head_snapc to keep track of which snapc the current epoch
of dirty data was dirtied under.  It is used by queue_cap_snap to set up
the cap_snap.  However, since we queue cap snaps for any dirty caps, not
just for dirty file data, we need to keep a valid i_head_snapc anytime
we have dirty|flushing caps.  This fixes a NULL pointer deref in
queue_cap_snap when writing back dirty caps without data (e.g.,
snaptest-authwb.sh).

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

1 files changed, 2 insertions, 1 deletions

diff --git a/fs/ceph/super.h b/fs/ceph/super.h
index b33929d8f287..c33897ae5725 100644
--- a/fs/ceph/super.h
+++ b/fs/ceph/super.h
@@ -344,7 +344,8 @@ struct ceph_inode_info {
         unsigned i_cap_exporting_issued;
         struct ceph_cap_reservation i_cap_migration_resv;
         struct list_head i_cap_snaps;   /* snapped state pending flush to mds */
-        struct ceph_snap_context *i_head_snapc;  /* set if wr_buffer_head > 0 */
+        struct ceph_snap_context *i_head_snapc;  /* set if wr_buffer_head > 0 or
+                                                    dirty|flushing caps */
         unsigned i_snap_caps;           /* cap bits for snapped files */
 
         int i_nr_by_mode[CEPH_FILE_MODE_NUM];  /* open file counts */