If device tree has hole, find_free_dev_extent() cannot find available
address properly.

The example below, has one BIG hole in device tree, and can only
allocate just one chunk in a transaction.

    item 9 key (1 DEV_EXTENT 273841913856) itemoff 15811 itemsize 48
        dev extent chunk_tree 3
        chunk objectid 256 chunk offset 272759783424 length 1073741824
    item 10 key (1 DEV_EXTENT 1071632089088) itemoff 15763 itemsize 48
        dev extent chunk_tree 3
        chunk objectid 256 chunk offset 1070549958656 length 1073741824
    item 11 key (1 DEV_EXTENT 1072705830912) itemoff 15715 itemsize 48
            dev extent chunk_tree 3
            chunk objectid 256 chunk offset 1071623700480 length

Signed-off-by: Forrest Liu <[email protected]>
---
 fs/btrfs/volumes.c | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index da7e0e1..61be789 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -1060,6 +1060,7 @@ static int contains_pending_extent(struct 
btrfs_trans_handle *trans,
        struct extent_map *em;
        struct list_head *search_list = &trans->transaction->pending_chunks;
        int ret = 0;
+       u64 physical_start = *start;
 
 again:
        list_for_each_entry(em, search_list, list) {
@@ -1070,9 +1071,9 @@ again:
                for (i = 0; i < map->num_stripes; i++) {
                        if (map->stripes[i].dev != device)
                                continue;
-                       if (map->stripes[i].physical >= *start + len ||
+                       if (map->stripes[i].physical >= physical_start + len ||
                            map->stripes[i].physical + em->orig_block_len <=
-                           *start)
+                           physical_start)
                                continue;
                        *start = map->stripes[i].physical +
                                em->orig_block_len;
@@ -1195,8 +1196,14 @@ again:
                         */
                        if (contains_pending_extent(trans, device,
                                                    &search_start,
-                                                   hole_size))
-                               hole_size = 0;
+                                                   hole_size)) {
+                               if (key.offset >= search_start)
+                                       hole_size = key_offset - search_start;
+                               else {
+                                       WARN_ON(1);
+                                       hole_size = 0;
+                               }
+                       }
 
                        if (hole_size > max_hole_size) {
                                max_hole_start = search_start;
-- 
1.9.1

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