2 files changed, 31 insertions, 2 deletions

diff --git a/fs/btrfs/dev-replace.c b/fs/btrfs/dev-replace.c
index 71fd99b48283..f26202621989 100644
--- a/fs/btrfs/dev-replace.c
+++ b/fs/btrfs/dev-replace.c
@@ -734,7 +734,12 @@ static int btrfs_dev_replace_start(struct btrfs_fs_info *fs_info,
 
 	btrfs_wait_ordered_roots(fs_info, U64_MAX, 0, (u64)-1);
 
-	/* Commit dev_replace state and reserve 1 item for it. */
+	/*
+	 * Commit dev_replace state and reserve 1 item for it.
+	 * This is crucial to ensure we won't miss copying extents for new block
+	 * groups that are allocated after we started the device replace, and
+	 * must be done after setting up the device replace state.
+	 */
 	trans = btrfs_start_transaction(root, 1);
 	if (IS_ERR(trans)) {
 		ret = PTR_ERR(trans);
diff --git a/fs/btrfs/scrub.c b/fs/btrfs/scrub.c
index 11089568b287..8cd713d37ad2 100644
--- a/fs/btrfs/scrub.c
+++ b/fs/btrfs/scrub.c
@@ -3699,6 +3699,31 @@ int scrub_enumerate_chunks(struct scrub_ctx *sctx,
 		if (!cache)
 			goto skip;
 
+		ASSERT(cache->start <= chunk_offset);
+		/*
+		 * We are using the commit root to search for device extents, so
+		 * that means we could have found a device extent item from a
+		 * block group that was deleted in the current transaction. The
+		 * logical start offset of the deleted block group, stored at
+		 * @chunk_offset, might be part of the logical address range of
+		 * a new block group (which uses different physical extents).
+		 * In this case btrfs_lookup_block_group() has returned the new
+		 * block group, and its start address is less than @chunk_offset.
+		 *
+		 * We skip such new block groups, because it's pointless to
+		 * process them, as we won't find their extents because we search
+		 * for them using the commit root of the extent tree. For a device
+		 * replace it's also fine to skip it, we won't miss copying them
+		 * to the target device because we have the write duplication
+		 * setup through the regular write path (by btrfs_map_block()),
+		 * and we have committed a transaction when we started the device
+		 * replace, right after setting up the device replace state.
+		 */
+		if (cache->start < chunk_offset) {
+			btrfs_put_block_group(cache);
+			goto skip;
+		}
+
 		if (sctx->is_dev_replace && btrfs_is_zoned(fs_info)) {
 			spin_lock(&cache->lock);
 			if (!cache->to_copy) {
@@ -3822,7 +3847,6 @@ int scrub_enumerate_chunks(struct scrub_ctx *sctx,
 		dev_replace->item_needs_writeback = 1;
 		up_write(&dev_replace->rwsem);
 
-		ASSERT(cache->start == chunk_offset);
 		ret = scrub_chunk(sctx, cache, scrub_dev, found_key.offset,
 				  dev_extent_len);