btrfs: extent-tree: Remove dead alignment check
diff mbox series

Message ID 20180723062246.2885-1-wqu@suse.com
State New
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Series
  • btrfs: extent-tree: Remove dead alignment check
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Commit Message

Qu Wenruo July 23, 2018, 6:22 a.m. UTC
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.

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 <wqu@suse.com>
---
 fs/btrfs/extent-tree.c | 7 +------
 1 file changed, 1 insertion(+), 6 deletions(-)

Comments

Qu Wenruo July 23, 2018, 6:39 a.m. UTC | #1
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 <wqu@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) {
>

Patch
diff mbox series

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) {