Btrfs: fix unprotected assignment of the left cursor for device replace

We were assigning new values to fields of the device replace object
without holding the respective lock after processing each device extent.
This is important for the left cursor field which can be accessed by a
concurrent task running __btrfs_map_block (which, correctly, takes the
device replace lock).
So change these fields while holding the device replace lock.

Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: Josef Bacik <jbacik@fb.com>

diff --git a/fs/btrfs/scrub.c b/fs/btrfs/scrub.c
index 1611572d47bd0ff32fdd0e6bed4afa069264f5b6..19a1eda703611c8162498657d660ae7516b5b269 100644 (file)
--- a/fs/btrfs/scrub.c
+++ b/fs/btrfs/scrub.c
@@ -3642,9 +3642,11 @@ int scrub_enumerate_chunks(struct scrub_ctx *sctx,
                        break;
                }
 
+               btrfs_dev_replace_lock(&fs_info->dev_replace, 1);
                dev_replace->cursor_right = found_key.offset + length;
                dev_replace->cursor_left = found_key.offset;
                dev_replace->item_needs_writeback = 1;
+               btrfs_dev_replace_unlock(&fs_info->dev_replace, 1);
                ret = scrub_chunk(sctx, scrub_dev, chunk_offset, length,
                                  found_key.offset, cache, is_dev_replace);
 
@@ -3718,8 +3720,10 @@ int scrub_enumerate_chunks(struct scrub_ctx *sctx,
                        break;
                }
 
+               btrfs_dev_replace_lock(&fs_info->dev_replace, 1);
                dev_replace->cursor_left = dev_replace->cursor_right;
                dev_replace->item_needs_writeback = 1;
+               btrfs_dev_replace_unlock(&fs_info->dev_replace, 1);
 skip:
                key.offset = found_key.offset + length;
                btrfs_release_path(path);