On Sat 21-05-22 21:42:16, 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>
Looks good. I'd just phrase the comment below a bit differently:
> + /*
> + * Because size must be less than or equal to
> + * EXT4_BLOCKS_PER_GROUP, 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.
> + */
> + start = max(start, round_down(ac->ac_o_ex.fe_logical,
> + EXT4_BLOCKS_PER_GROUP(ac->ac_sb)));
> +
Can we make the comment like:
/*
* For tiny groups (smaller than 8MB) the chosen allocation
* alignment may be larger than group size. Make sure the alignment
* does not move allocation to a different group which makes mballoc
* fail assertions later.
*/
With that feel free to add:
Reviewed-by: Jan Kara <jack@xxxxxxx>
Honza
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
