On 2018年07月23日 14:22, Qu Wenruo wrote:
> In find_free_extent() under checks: tag, we have the following code
>
> ------
> search_start = ALIGN(offset, fs_info->stripesize);
> /* move on to the next group */
> if (search_start + num_bytes >
> block_group->key.objectid + block_group->key.offset) {
> btrfs_add_free_space(block_group, offset, num_bytes);
> goto loop;
> }
> if (offset < search_start)
> btrfs_add_free_space(block_group, offset,
> search_start - offset);
> BUG_ON(offset > search_start);
> ------
>
> However ALIGN() is rounding down, thus @search_start <= @offset.
Well, ALIGN() is rounding up, so this is completely wrong.
But still we have some conflicting BUG_ON() against ALIGN().
I'll update the patch and hopes no one found my stupid error.
Thanks,
Qu
>
> That later (offset < search_start) check will never be true, but that
> BUG_ON(offset > search_start) can be triggered as long as our @offset is
> not aligned to @stripesize.
>
> However we never has such report on this BUG_ON(), which means the
> search result @offset is always aligned to @fs_info->stripesize (which
> is also set to sector size at mkfs time), or it's handled by block group
> range check.
>
> Anyway, remove such dead unalignment check.
>
> Signed-off-by: Qu Wenruo <w...@suse.com>
> ---
> fs/btrfs/extent-tree.c | 7 +------
> 1 file changed, 1 insertion(+), 6 deletions(-)
>
> diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
> index f18e86177067..48a2aec7dc59 100644
> --- a/fs/btrfs/extent-tree.c
> +++ b/fs/btrfs/extent-tree.c
> @@ -7754,7 +7754,7 @@ static noinline int find_free_extent(struct
> btrfs_fs_info *fs_info,
> goto loop;
> }
> checks:
> - search_start = ALIGN(offset, fs_info->stripesize);
> + search_start = round_down(offset, fs_info->stripesize);
>
> /* move on to the next group */
> if (search_start + num_bytes >
> @@ -7763,11 +7763,6 @@ static noinline int find_free_extent(struct
> btrfs_fs_info *fs_info,
> goto loop;
> }
>
> - if (offset < search_start)
> - btrfs_add_free_space(block_group, offset,
> - search_start - offset);
> - BUG_ON(offset > search_start);
> -
> ret = btrfs_add_reserved_bytes(block_group, ram_bytes,
> num_bytes, delalloc);
> if (ret == -EAGAIN) {
>
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