Re: [PATCH 4/4] btrfs: convert: Avoid allocating metadata extent crossing stripe boundary

[Qu Wenruo]

David Sterba wrote on 2015/07/24 14:34 +0200:

On Thu, Jul 23, 2015 at 05:18:10PM +0800, Qu Wenruo wrote:

@@ -246,6 +247,14 @@ static int custom_alloc_extent(struct btrfs_root *root, 
u64 num_bytes,
                        continue;
                }

+               if (metadata) {
+                       BUG_ON(num_bytes != root->nodesize);

This caught my attention and looking at possible values of num_bytes,
this can crash:

1291         for (last_byte = 0; last_byte < first_free; last_byte += 
sectorsize) {
1292                 ret = custom_alloc_extent(root, sectorsize, 0, &key, 0);

where sectorsize == num_bytes.

For that case, the last 0 means that's a data block,
and won't comes to the BUG_ON, as it is only designed for metadata.
And for metadata allocation, the size will only be nodes/leafsize

Thanks,
Qu

+                       if (check_crossing_stripes(start, num_bytes)) {
+                               last = round_down(start + num_bytes,
+                                                 BTRFS_STRIPE_LEN);
+                               continue;
+                       }
+               }
                clear_extent_dirty(&root->fs_info->free_space_cache,
                                   start, start + num_bytes - 1, 0);

@@ -1280,7 +1289,7 @@ static int create_ext2_image(struct btrfs_root *root, 
ext2_filsys ext2_fs,
         * special, we can't rely on relocate_extents_range to relocate it.
         */
        for (last_byte = 0; last_byte < first_free; last_byte += sectorsize) {
-               ret = custom_alloc_extent(root, sectorsize, 0, &key);
+               ret = custom_alloc_extent(root, sectorsize, 0, &key, 0);

Same here.

-                       ret = custom_alloc_extent(root, sectorsize, 0, &key);
+                       ret = custom_alloc_extent(root, sectorsize, 0, &key, 0);

And here.

I hope there's a way how to avoid the BUG_ON at all.

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