linux-ext4 - Re: [PATCH v3 1/3] ext4: fix bug_on ext4_mb_use_inode

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Date:   Mon, 30 May 2022 10:12:48 +0800
From:   Baokun Li <libaokun1@...wei.com>
To:     Ritesh Harjani <ritesh.list@...il.com>
CC:     <linux-ext4@...r.kernel.org>, <tytso@....edu>,
        <adilger.kernel@...ger.ca>, <jack@...e.cz>, <lczerner@...hat.com>,
        <linux-kernel@...r.kernel.org>, <yi.zhang@...wei.com>,
        <yebin10@...wei.com>, <yukuai3@...wei.com>,
        Hulk Robot <hulkci@...wei.com>,
        Baokun Li <libaokun1@...wei.com>
Subject: Re: [PATCH v3 1/3] ext4: fix bug_on ext4_mb_use_inode_pa

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@...wei.com>
>> Signed-off-by: Baokun Li <libaokun1@...wei.com>
>> ---
>> 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@...il.com>
>
>>   fs/ext4/mballoc.c | 9 +++++++++
>>   1 file changed, 9 insertions(+)
>>
> .
>
Thank you for your review!
-- 
With Best Regards,
Baokun Li