ceph: fix null pointer dereference in send_mds_reconnect()

sb->s_root can be null when umounting

Signed-off-by: Yan, Zheng <zyan@redhat.com>

diff --git a/fs/ceph/mds_client.c b/fs/ceph/mds_client.c
index fd5585b..0a2eb32 100644 (file)
--- a/fs/ceph/mds_client.c
+++ b/fs/ceph/mds_client.c
@@ -2892,7 +2892,8 @@ static void send_mds_reconnect(struct ceph_mds_client *mdsc,
        spin_unlock(&session->s_cap_lock);
 
        /* trim unused caps to reduce MDS's cache rejoin time */
-       shrink_dcache_parent(mdsc->fsc->sb->s_root);
+       if (mdsc->fsc->sb->s_root)
+               shrink_dcache_parent(mdsc->fsc->sb->s_root);
 
        ceph_con_close(&session->s_con);
        ceph_con_open(&session->s_con,