ceph: fix iterate_caps removal race

We need to be able to iterate over all caps on a session with a
possibly slow callback on each cap.  To allow this, we used to
prevent cap reordering while we were iterating.  However, we were
not safe from races with removal: removing the 'next' cap would
make the next pointer from list_for_each_entry_safe be invalid,
and cause a lock up or similar badness.

Instead, we keep an iterator pointer in the session pointing to
the current cap.  As before, we avoid reordering.  For removal,
if the cap isn't the current cap we are iterating over, we are
fine.  If it is, we clear cap->ci (to mark the cap as pending
removal) but leave it in the session list.  In iterate_caps, we
can safely finish removal and get the next cap pointer.

While we're at it, clean up put_cap to not take a cap reservation
context, as it was never used.

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

1 files changed, 1 insertions, 1 deletions

diff --git a/fs/ceph/mds_client.h b/fs/ceph/mds_client.h
index 9d6b90173879..961cc6f65878 100644
--- a/fs/ceph/mds_client.h
+++ b/fs/ceph/mds_client.h
@@ -114,7 +114,7 @@ struct ceph_mds_session {
         int               s_num_cap_releases;
         struct list_head  s_cap_releases; /* waiting cap_release messages */
         struct list_head  s_cap_releases_done; /* ready to send */
-        bool              s_iterating_caps;
+        struct ceph_cap  *s_cap_iterator;
 
         /* protected by mutex */
         struct list_head  s_cap_flushing;     /* inodes w/ flushing caps */