ceph: fix comments over ceph_add_cap

We actually need the ci->i_ceph_lock here. The necessity of the s_mutex
is less clear. Also add a lockdep assertion for the i_ceph_lock.
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: "Yan, Zheng" <zyan@redhat.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

fs/ceph/caps.c

@@ -597,7 +597,7 @@ static void __check_cap_issue(struct ceph_inode_info *ci, struct ceph_cap *cap,
 /*
  * Add a capability under the given MDS session.
  *
- * Caller should hold session snap_rwsem (read) and s_mutex.
+ * Caller should hold session snap_rwsem (read) and ci->i_ceph_lock
  *
  * @fmode is the open file mode, if we are opening a file, otherwise
  * it is < 0.  (This is so we can atomically add the cap and add an
@@ -616,6 +616,8 @@ void ceph_add_cap(struct inode *inode,
 	int actual_wanted;
 	u32 gen;
 
+	lockdep_assert_held(&ci->i_ceph_lock);
+
 	dout("add_cap %p mds%d cap %llx %s seq %d\n", inode,
 	     session->s_mds, cap_id, ceph_cap_string(issued), seq);