On 09/14/2018 07:37 AM, Qu Wenruo wrote:
On 2018/9/13 上午4:49, damenly.su@xxxxxxxxx wrote:
From: Su Yue <suy.fnst@xxxxxxxxxxxxxx>
In check_fs_roots_lowmem(), we do search and follow the resulted path
to call check_fs_root(), then call btrfs_next_item() to check next
root.
However, if repair is enabled, the root tree can be cowed, the
existed path can cause strange errors.
Solution:
If repair, save the key before calling check_fs_root,
search the saved key again before checking next root.
Both reason and solution looks good.
Signed-off-by: Su Yue <suy.fnst@xxxxxxxxxxxxxx>
---
check/mode-lowmem.c | 15 +++++++++++++++
1 file changed, 15 insertions(+)
diff --git a/check/mode-lowmem.c b/check/mode-lowmem.c
index 89a304bbdd69..8fc9edab1d66 100644
--- a/check/mode-lowmem.c
+++ b/check/mode-lowmem.c
@@ -4967,9 +4967,13 @@ int check_fs_roots_lowmem(struct btrfs_fs_info *fs_info)
}
while (1) {
+ struct btrfs_key saved_key;
+
node = path.nodes[0];
slot = path.slots[0];
btrfs_item_key_to_cpu(node, &key, slot);
+ if (repair)
+ saved_key = key;
if (key.objectid > BTRFS_LAST_FREE_OBJECTID)
goto out;
if (key.type == BTRFS_ROOT_ITEM_KEY &&
@@ -5000,6 +5004,17 @@ int check_fs_roots_lowmem(struct btrfs_fs_info *fs_info)
err |= ret;
}
next:
+ /*
+ * Since root tree can be cowed during repair,
+ * here search the saved key again.
+ */
+ if (repair) {
+ btrfs_release_path(&path);
+ ret = btrfs_search_slot(NULL, fs_info->tree_root,
+ &saved_key, &path, 0, 0);
+ /* Repair never deletes trees, search must succeed. */
+ BUG_ON(ret);
But this doesn't look good to me.
Your assumption here is valid (at least for now), but it's possible that
some tree blocks get corrupted in a large root tree, and in that case,
we could still read part of the root tree, but btrfs_search_slot() could
still return -EIO for certain search key.
So I still prefer to do some error handling other than BUG_ON(ret).
Okay, will try it.
Thanks,
Su
Thanks,
Qu
+ }
ret = btrfs_next_item(tree_root, &path);
if (ret > 0)
goto out;
