[PATCH] btrfs-progs: fix false alert on tree block crossing 64K page boundary

[PATCH] btrfs-progs: fix false alert on tree block crossing 64K page boundary

[Qu Wenruo]

[BUG]
When btrfs-check is executed on even newly created fs, it can report
tree blocks crossing 64K page boundary like this:

  Opening filesystem to check...
  Checking filesystem on /dev/test/test
  UUID: 80d734c8-dcbc-411b-9623-a10bd9e7767f
  [1/7] checking root items
  [2/7] checking extents
  WARNING: tree block [30523392, 30539776) crosses 64K page boudnary, may cause problem for 64K page system
  [3/7] checking free space cache
  [4/7] checking fs roots
  [5/7] checking only csums items (without verifying data)
  [6/7] checking root refs
  [7/7] checking quota groups skipped (not enabled on this FS)
  found 131072 bytes used, no error found
  total csum bytes: 0
  total tree bytes: 131072
  total fs tree bytes: 32768
  total extent tree bytes: 16384
  btree space waste bytes: 125199
  file data blocks allocated: 0
   referenced 0

[CAUSE]
Tree block [30523392, 30539776) is at the last 16K slot of page.
As 30523392 % 65536 = 49152, and 30539776 % 65536 = 0.

The cross boundary check is using exclusive end, which causes false
alerts.

[FIX]
Use inclusive end to do the cross 64K boundary check.

Reported-by: Wang Yugui <wangyugui@e16-tech.com>
Fixes: fc38ae7f4826 ("btrfs-progs: check: detect and warn about tree blocks crossing 64K page boundary")
Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 check/mode-common.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/check/mode-common.h b/check/mode-common.h
index 8fdeb7f6be0a..3107b00c48bf 100644
--- a/check/mode-common.h
+++ b/check/mode-common.h
@@ -186,7 +186,7 @@ int get_extent_item_generation(u64 bytenr, u64 *gen_ret);
 static inline void btrfs_check_subpage_eb_alignment(u64 start, u32 len)
 {
 	if (start / BTRFS_MAX_METADATA_BLOCKSIZE !=
-	    (start + len) / BTRFS_MAX_METADATA_BLOCKSIZE)
+	    (start + len - 1) / BTRFS_MAX_METADATA_BLOCKSIZE)
 		warning(
 "tree block [%llu, %llu) crosses 64K page boudnary, may cause problem for 64K page system",
 			start, start + len);
-- 
2.30.1

Re: [PATCH] btrfs-progs: fix false alert on tree block crossing 64K page boundary

[Wang Yugui]

Hi,

It passed the test. Thanks a lot.

Best Regards
Wang Yugui (wangyugui@e16-tech.com)
2021/03/06

> [BUG]
> When btrfs-check is executed on even newly created fs, it can report
> tree blocks crossing 64K page boundary like this:
> 
>   Opening filesystem to check...
>   Checking filesystem on /dev/test/test
>   UUID: 80d734c8-dcbc-411b-9623-a10bd9e7767f
>   [1/7] checking root items
>   [2/7] checking extents
>   WARNING: tree block [30523392, 30539776) crosses 64K page boudnary, may cause problem for 64K page system
>   [3/7] checking free space cache
>   [4/7] checking fs roots
>   [5/7] checking only csums items (without verifying data)
>   [6/7] checking root refs
>   [7/7] checking quota groups skipped (not enabled on this FS)
>   found 131072 bytes used, no error found
>   total csum bytes: 0
>   total tree bytes: 131072
>   total fs tree bytes: 32768
>   total extent tree bytes: 16384
>   btree space waste bytes: 125199
>   file data blocks allocated: 0
>    referenced 0
> 
> [CAUSE]
> Tree block [30523392, 30539776) is at the last 16K slot of page.
> As 30523392 % 65536 = 49152, and 30539776 % 65536 = 0.
> 
> The cross boundary check is using exclusive end, which causes false
> alerts.
> 
> [FIX]
> Use inclusive end to do the cross 64K boundary check.
> 
> Reported-by: Wang Yugui <wangyugui@e16-tech.com>
> Fixes: fc38ae7f4826 ("btrfs-progs: check: detect and warn about tree blocks crossing 64K page boundary")
> Signed-off-by: Qu Wenruo <wqu@suse.com>
> ---
>  check/mode-common.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/check/mode-common.h b/check/mode-common.h
> index 8fdeb7f6be0a..3107b00c48bf 100644
> --- a/check/mode-common.h
> +++ b/check/mode-common.h
> @@ -186,7 +186,7 @@ int get_extent_item_generation(u64 bytenr, u64 *gen_ret);
>  static inline void btrfs_check_subpage_eb_alignment(u64 start, u32 len)
>  {
>  	if (start / BTRFS_MAX_METADATA_BLOCKSIZE !=
> -	    (start + len) / BTRFS_MAX_METADATA_BLOCKSIZE)
> +	    (start + len - 1) / BTRFS_MAX_METADATA_BLOCKSIZE)
>  		warning(
>  "tree block [%llu, %llu) crosses 64K page boudnary, may cause problem for 64K page system",
>  			start, start + len);
> -- 
> 2.30.1

Re: [PATCH] btrfs-progs: fix false alert on tree block crossing 64K page boundary

[David Sterba]

On Sat, Mar 06, 2021 at 08:40:19AM +0800, Qu Wenruo wrote:
> [BUG]
> When btrfs-check is executed on even newly created fs, it can report
> tree blocks crossing 64K page boundary like this:
> 
>   Opening filesystem to check...
>   Checking filesystem on /dev/test/test
>   UUID: 80d734c8-dcbc-411b-9623-a10bd9e7767f
>   [1/7] checking root items
>   [2/7] checking extents
>   WARNING: tree block [30523392, 30539776) crosses 64K page boudnary, may cause problem for 64K page system
>   [3/7] checking free space cache
>   [4/7] checking fs roots
>   [5/7] checking only csums items (without verifying data)
>   [6/7] checking root refs
>   [7/7] checking quota groups skipped (not enabled on this FS)
>   found 131072 bytes used, no error found
>   total csum bytes: 0
>   total tree bytes: 131072
>   total fs tree bytes: 32768
>   total extent tree bytes: 16384
>   btree space waste bytes: 125199
>   file data blocks allocated: 0
>    referenced 0
> 
> [CAUSE]
> Tree block [30523392, 30539776) is at the last 16K slot of page.
> As 30523392 % 65536 = 49152, and 30539776 % 65536 = 0.
> 
> The cross boundary check is using exclusive end, which causes false
> alerts.
> 
> [FIX]
> Use inclusive end to do the cross 64K boundary check.
> 
> Reported-by: Wang Yugui <wangyugui@e16-tech.com>
> Fixes: fc38ae7f4826 ("btrfs-progs: check: detect and warn about tree blocks crossing 64K page boundary")
> Signed-off-by: Qu Wenruo <wqu@suse.com>

Thanks. I've extended the 001 test for mkfs to actually check for any
check warnings right after mkfs, covering all profiles and
single/multiple setups.