Re: [PATCH v3 1/3] ext4: fix bug_on ext4_mb_use_inode_pa

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在 2022/5/28 23:10, Ritesh Harjani 写道:
On 22/05/28 07:00PM, Baokun Li wrote:
Hulk Robot reported a BUG_ON:
==================================================================
kernel BUG at fs/ext4/mballoc.c:3211!
[...]
RIP: 0010:ext4_mb_mark_diskspace_used.cold+0x85/0x136f
[...]
Call Trace:
  ext4_mb_new_blocks+0x9df/0x5d30
  ext4_ext_map_blocks+0x1803/0x4d80
  ext4_map_blocks+0x3a4/0x1a10
  ext4_writepages+0x126d/0x2c30
  do_writepages+0x7f/0x1b0
  __filemap_fdatawrite_range+0x285/0x3b0
  file_write_and_wait_range+0xb1/0x140
  ext4_sync_file+0x1aa/0xca0
  vfs_fsync_range+0xfb/0x260
  do_fsync+0x48/0xa0
[...]
==================================================================

Above issue may happen as follows:
-------------------------------------
do_fsync
  vfs_fsync_range
   ext4_sync_file
    file_write_and_wait_range
     __filemap_fdatawrite_range
      do_writepages
       ext4_writepages
        mpage_map_and_submit_extent
         mpage_map_one_extent
          ext4_map_blocks
           ext4_mb_new_blocks
            ext4_mb_normalize_request
             >>> start + size <= ac->ac_o_ex.fe_logical
            ext4_mb_regular_allocator
             ext4_mb_simple_scan_group
              ext4_mb_use_best_found
               ext4_mb_new_preallocation
                ext4_mb_new_inode_pa
                 ext4_mb_use_inode_pa
                  >>> set ac->ac_b_ex.fe_len <= 0
            ext4_mb_mark_diskspace_used
             >>> BUG_ON(ac->ac_b_ex.fe_len <= 0);

we can easily reproduce this problem with the following commands:
	`fallocate -l100M disk`
	`mkfs.ext4 -b 1024 -g 256 disk`
	`mount disk /mnt`
	`fsstress -d /mnt -l 0 -n 1000 -p 1`

The size must be smaller than or equal to EXT4_BLOCKS_PER_GROUP.
Therefore, "start + size <= ac->ac_o_ex.fe_logical" may occur
when the size is truncated. So start should be the start position of
the group where ac_o_ex.fe_logical is located after alignment.
In addition, when the value of fe_logical or EXT4_BLOCKS_PER_GROUP
is very large, the value calculated by start_off is more accurate.

Fixes: cd648b8a8fd5 ("ext4: trim allocation requests to group size")
Reported-by: Hulk Robot <hulkci@xxxxxxxxxx>
Signed-off-by: Baokun Li <libaokun1@xxxxxxxxxx>
---
V1->V2:
	Replace round_down() with rounddown().
	Modified comments.
V2->V3:
	Convert EXT4_BLOCKS_PER_GROUP type to ext4_lblk_t
	to avoid compilation warnings.
Looks good to me. Feel free to add -

Reviewed-by: Ritesh Harjani <ritesh.list@xxxxxxxxx>

  fs/ext4/mballoc.c | 9 +++++++++
  1 file changed, 9 insertions(+)

.

Thank you for your review!
--
With Best Regards,
Baokun Li




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