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

[Baokun Li]

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