diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 1f192a581fb2..ac612c02ced9 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -790,6 +790,13 @@ bool cleanup_offline_cgwb(struct bdi_writeback *wb)
 		new_wb = &wb->bdi->wb; /* wb_get() is noop for bdi's wb */
 
 	nr = 0;
+	/*
+	 * The scan moves walked inodes to the newest end of b_dirty_time,
+	 * past ones it didn't reach. If one of those was dirtied after a
+	 * sync's cutoff, the sync's queue_io() stops there and misses the
+	 * moved ones. Exclude syncs as process_inode_switch_wbs() does.
+	 */
+	down_read(&wb->bdi->wb_switch_rwsem);
 	spin_lock(&wb->list_lock);
 	/*
 	 * In addition to the inodes that have completed writeback, also switch
@@ -804,6 +811,7 @@ bool cleanup_offline_cgwb(struct bdi_writeback *wb)
 		restart = isw_prepare_wbs_switch(new_wb, isw, &wb->b_dirty_time,
 						 &nr);
 	spin_unlock(&wb->list_lock);
+	up_read(&wb->bdi->wb_switch_rwsem);
 
 	/* no attached inodes? bail out */
 	if (nr == 0) {