ceph: re-request max_size if cap auth changes

If the auth cap migrates to another MDS, clear requested_max_size so that
we resend any pending max_size increase requests.  This fixes potential
hangs on writes that extend a file and race with an cap migration between
MDSs.
Signed-off-by: Sage Weil <sage@newdream.net>

fs/ceph/caps.c

@@ -2689,6 +2689,11 @@ static void handle_cap_import(struct ceph_mds_client *mdsc,
 		     NULL /* no caps context */);
 	try_flush_caps(inode, session, NULL);
 	up_read(&mdsc->snap_rwsem);
+
+	/* make sure we re-request max_size, if necessary */
+	spin_lock(&inode->i_lock);
+	ci->i_requested_max_size = 0;
+	spin_unlock(&inode->i_lock);
 }
 
 /*