1 files changed, 65 insertions, 1 deletions

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 936c3137c646..7e8d8169779d 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -2253,11 +2253,69 @@ static int add_pending_csums(struct btrfs_trans_handle *trans,
 	return 0;
 }
 
+static int btrfs_find_new_delalloc_bytes(struct btrfs_inode *inode,
+					 const u64 start,
+					 const u64 len,
+					 struct extent_state **cached_state)
+{
+	u64 search_start = start;
+	const u64 end = start + len - 1;
+
+	while (search_start < end) {
+		const u64 search_len = end - search_start + 1;
+		struct extent_map *em;
+		u64 em_len;
+		int ret = 0;
+
+		em = btrfs_get_extent(inode, NULL, 0, search_start, search_len);
+		if (IS_ERR(em))
+			return PTR_ERR(em);
+
+		if (em->block_start != EXTENT_MAP_HOLE)
+			goto next;
+
+		em_len = em->len;
+		if (em->start < search_start)
+			em_len -= search_start - em->start;
+		if (em_len > search_len)
+			em_len = search_len;
+
+		ret = set_extent_bit(&inode->io_tree, search_start,
+				     search_start + em_len - 1,
+				     EXTENT_DELALLOC_NEW,
+				     NULL, cached_state, GFP_NOFS);
+next:
+		search_start = extent_map_end(em);
+		free_extent_map(em);
+		if (ret)
+			return ret;
+	}
+	return 0;
+}
+
 int btrfs_set_extent_delalloc(struct btrfs_inode *inode, u64 start, u64 end,
 			      unsigned int extra_bits,
 			      struct extent_state **cached_state)
 {
 	WARN_ON(PAGE_ALIGNED(end));
+
+	if (start >= i_size_read(&inode->vfs_inode) &&
+	    !(inode->flags & BTRFS_INODE_PREALLOC)) {
+		/*
+		 * There can't be any extents following eof in this case so just
+		 * set the delalloc new bit for the range directly.
+		 */
+		extra_bits |= EXTENT_DELALLOC_NEW;
+	} else {
+		int ret;
+
+		ret = btrfs_find_new_delalloc_bytes(inode, start,
+						    end + 1 - start,
+						    cached_state);
+		if (ret)
+			return ret;
+	}
+
 	return set_extent_delalloc(&inode->io_tree, start, end, extra_bits,
 				   cached_state);
 }
@@ -9672,10 +9730,16 @@ static int __btrfs_prealloc_file_range(struct inode *inode, int mode,
 		 * clear_offset by our extent size.
 		 */
 		clear_offset += ins.offset;
-		btrfs_dec_block_group_reservations(fs_info, ins.objectid);
 
 		last_alloc = ins.offset;
 		trans = insert_prealloc_file_extent(trans, inode, &ins, cur_offset);
+		/*
+		 * Now that we inserted the prealloc extent we can finally
+		 * decrement the number of reservations in the block group.
+		 * If we did it before, we could race with relocation and have
+		 * relocation miss the reserved extent, making it fail later.
+		 */
+		btrfs_dec_block_group_reservations(fs_info, ins.objectid);
 		if (IS_ERR(trans)) {
 			ret = PTR_ERR(trans);
 			btrfs_free_reserved_extent(fs_info, ins.objectid,