Re: [PATCH v2 2/5] ext4: Add unit test of ext4_mb_generate_buddy

[Guenter Roeck <linux@roeck-us.net>]

On 3/22/24 02:27, Kemeng Shi wrote:
> 
> 
> on 3/21/2024 3:16 PM, Kemeng Shi wrote:
>>
>>
>> on 3/21/2024 12:23 AM, Guenter Roeck wrote:
>>> Hi,
>>>
>>> On Wed, Jan 03, 2024 at 06:48:57PM +0800, Kemeng Shi wrote:
>>>> Add unit test of ext4_mb_generate_buddy
>>>>
>>>> Signed-off-by: Kemeng Shi <shikemeng@huaweicloud.com>
>>>
>>> With this and other new ext4 tests test in the tree, I see a variety
>>> of backtraces in the upstream kernel if debug options are enabled.
>>> An example is
>>>
>>> [    6.821447]         KTAP version 1
>>> [    6.821769]         # Subtest: test_mb_generate_buddy
>>> [    6.824787] =============================================================================
>>> [    6.825568] BUG inode_cache (Tainted: G                 N): Padding overwritten. 0xfffff80006223f68-0xfffff80006223f6f @offset=16232
>>> ...
>>> [    6.894341] ok 7 ext4_inode_test
>>> [    6.895411] =============================================================================
>>> [    6.895777] BUG inode_cache (Tainted: G    B            N): Padding overwritten. 0xfffff80006223f68-0xfffff80006223f6f @offset=16232
>>>
>>> Another example, from another test run, is
>>>
>>> [    3.938551]         # Subtest: test_new_blocks_simple
>>> [    3.947171]         ok 1 block_bits=10 cluster_bits=3 blocks_per_group=8192 group_count=4 desc_size=64
>>> [    3.952988]         ok 2 block_bits=12 cluster_bits=3 blocks_per_group=8192 group_count=4 desc_size=64
>>> [    3.958403]         ok 3 block_bits=16 cluster_bits=3 blocks_per_group=8192 group_count=4 desc_size=64
>>> [    3.958890] =============================================================================
>>> [    3.959159] BUG inode_cache (Tainted: G                 N): Padding overwritten. 0xffff8de881adbf68-0xffff8de881adbf6f @offset=16232
>>>
>>> Another one:
>>>
>>> [   18.730473]         # Subtest: test_new_blocks_simple
>>> [   18.760547]         ok 1 block_bits=10 cluster_bits=3 blocks_per_group=8192 group_count=4 desc_size=64
>>> [   18.778477] ==================================================================
>>> [   18.778950] BUG: KFENCE: out-of-bounds write in ext4_mb_init+0x5d7/0xa60
>>>
>>> This is just a sample, taken from a quick look at test results.
>>>
>>> Are those backtraces expected ? If so, would it be possible to execute the
>>> tests without generating such backtraces ? The backtraces, if intentional,
>>> hide real problems in the noise.
>> Thanks for the report. The backtrace is not expected, I will look into this. Thansk!
>>>
> Hi Guenter, I could not reproduce this in my local vm. From the reported backtraces, it's
> likely there is a out-of-bounds write to sbi->s_buddy_cache. I try to fix this in [1] and
> it works fine in my local vm. I wish this work for you to elimate the reported nosie.
> Look forward to your reply, Thanks.
> 

You would need to have CONFIG_SLUB_DEBUG=y, CONFIG_SLUB_DEBUG_ON=y, and CONFIG_KFENCE=y
to see the problems.

Guenter