ceph: handle race between cap reconnect and cap release

When a cap get released while composing the cap reconnect message.
We should skip queuing the release message if the cap hasn't been
added to the cap reconnect message.

Signed-off-by: Yan, Zheng <zheng.z.yan@intel.com>
Reviewed-by: Sage Weil <sage@inktank.com>
diff --git a/fs/ceph/caps.c b/fs/ceph/caps.c
index d2d6e40..3c0a4bd 100644
--- a/fs/ceph/caps.c
+++ b/fs/ceph/caps.c
@@ -909,7 +909,13 @@
 
 	/* remove from session list */
 	spin_lock(&session->s_cap_lock);
-	if (queue_release)
+	/*
+	 * s_cap_reconnect is protected by s_cap_lock. no one changes
+	 * s_cap_gen while session is in the reconnect state.
+	 */
+	if (queue_release &&
+	    (!session->s_cap_reconnect ||
+	     cap->cap_gen == session->s_cap_gen))
 		__queue_cap_release(session, ci->i_vino.ino, cap->cap_id,
 				    cap->mseq, cap->issue_seq);