ceph: quota: cache inode pointer in ceph_snap_realm

Keep a pointer to the inode in struct ceph_snap_realm.  This allows to
optimize functions that walk the realms hierarchy (e.g. in quotas).

Signed-off-by: Luis Henriques <lhenriques@suse.com>
Reviewed-by: "Yan, Zheng" <zyan@redhat.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
diff --git a/fs/ceph/inode.c b/fs/ceph/inode.c
index 50ccae1..8ea11b1 100644
--- a/fs/ceph/inode.c
+++ b/fs/ceph/inode.c
@@ -551,6 +551,9 @@
 		dout(" dropping residual ref to snap realm %p\n", realm);
 		spin_lock(&realm->inodes_with_caps_lock);
 		list_del_init(&ci->i_snap_realm_item);
+		ci->i_snap_realm = NULL;
+		if (realm->ino == ci->i_vino.ino)
+			realm->inode = NULL;
 		spin_unlock(&realm->inodes_with_caps_lock);
 		ceph_put_snap_realm(mdsc, realm);
 	}