ceph: add helper function that forcibly reconnects to ceph cluster.

It closes mds sessions, drop all caps and invalidates page caches,
then use new entity address to reconnect to the cluster.

After reconnect, all dirty data/metadata are dropped, file locks
get lost sliently. Open files continue to work because client will
try renewing caps on later read/write.
Signed-off-by: "Yan, Zheng" <zyan@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

fs/ceph/mds_client.c

@@ -1394,9 +1394,12 @@ static int remove_session_caps_cb(struct inode *inode, struct ceph_cap *cap,
 		struct ceph_cap_flush *cf;
 		struct ceph_mds_client *mdsc = fsc->mdsc;
 
-		if (ci->i_wrbuffer_ref > 0 &&
-		    READ_ONCE(fsc->mount_state) == CEPH_MOUNT_SHUTDOWN)
-			invalidate = true;
+		if (READ_ONCE(fsc->mount_state) == CEPH_MOUNT_SHUTDOWN) {
+			if (inode->i_data.nrpages > 0)
+				invalidate = true;
+			if (ci->i_wrbuffer_ref > 0)
+				mapping_set_error(&inode->i_data, -EIO);
+		}
 
 		while (!list_empty(&ci->i_cap_flush_list)) {
 			cf = list_first_entry(&ci->i_cap_flush_list,
@@ -4369,7 +4372,12 @@ void ceph_mdsc_force_umount(struct ceph_mds_client *mdsc)
 		session = __ceph_lookup_mds_session(mdsc, mds);
 		if (!session)
 			continue;
+
+		if (session->s_state == CEPH_MDS_SESSION_REJECTED)
+			__unregister_session(mdsc, session);
+		__wake_requests(mdsc, &session->s_waiting);
 		mutex_unlock(&mdsc->mutex);
+
 		mutex_lock(&session->s_mutex);
 		__close_session(mdsc, session);
 		if (session->s_state == CEPH_MDS_SESSION_CLOSING) {
@@ -4378,6 +4386,7 @@ void ceph_mdsc_force_umount(struct ceph_mds_client *mdsc)
 		}
 		mutex_unlock(&session->s_mutex);
 		ceph_put_mds_session(session);
+
 		mutex_lock(&mdsc->mutex);
 		kick_requests(mdsc, mds);
 	}

fs/ceph/super.c

@@ -829,7 +829,6 @@ static void ceph_umount_begin(struct super_block *sb)
 	fsc->mount_state = CEPH_MOUNT_SHUTDOWN;
 	ceph_osdc_abort_requests(&fsc->client->osdc, -EIO);
 	ceph_mdsc_force_umount(fsc->mdsc);
-	return;
 }
 
 static int ceph_remount(struct super_block *sb, int *flags, char *data)
@@ -1152,6 +1151,31 @@ static struct file_system_type ceph_fs_type = {
 };
 MODULE_ALIAS_FS("ceph");
 
+int ceph_force_reconnect(struct super_block *sb)
+{
+	struct ceph_fs_client *fsc = ceph_sb_to_client(sb);
+	int err = 0;
+
+	ceph_umount_begin(sb);
+
+	/* Make sure all page caches get invalidated.
+	 * see remove_session_caps_cb() */
+	flush_workqueue(fsc->inode_wq);
+
+	/* In case that we were blacklisted. This also reset
+	 * all mon/osd connections */
+	ceph_reset_client_addr(fsc->client);
+
+	ceph_osdc_clear_abort_err(&fsc->client->osdc);
+	fsc->mount_state = CEPH_MOUNT_MOUNTED;
+
+	if (sb->s_root) {
+		err = __ceph_do_getattr(d_inode(sb->s_root), NULL,
+					CEPH_STAT_CAP_INODE, true);
+	}
+	return err;
+}
+
 static int __init init_ceph(void)
 {
 	int ret = init_caches();

fs/ceph/super.h

@@ -846,7 +846,8 @@ static inline int default_congestion_kb(void)
 }
 
 
-
+/* super.c */
+extern int ceph_force_reconnect(struct super_block *sb);
 /* snap.c */
 struct ceph_snap_realm *ceph_lookup_snap_realm(struct ceph_mds_client *mdsc,
 					       u64 ino);