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Subject: Re: [PATCH v2 2/5] ext4: Add unit test of ext4_mb_generate_buddy
From: Kemeng Shi <shikemeng@huaweicloud.com>
To: Guenter Roeck <linux@roeck-us.net>
Cc: tytso@mit.edu, adilger.kernel@dilger.ca, linux-ext4@vger.kernel.org,
 linux-kernel@vger.kernel.org
References: <20240103104900.464789-1-shikemeng@huaweicloud.com>
 <20240103104900.464789-3-shikemeng@huaweicloud.com>
 <30a8ce01-84d1-48ef-a93d-d14cc61723e3@roeck-us.net>
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Message-ID: <03b1cc3d-de26-e473-68c6-8c904472095e@huaweicloud.com>
Date: Fri, 22 Mar 2024 17:27:13 +0800
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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.

Kemeng

[1] https://lore.kernel.org/linux-ext4/20240322165518.8147-1-shikemeng@huaweicloud.com/T/#u

>> Thanks,
>> Guenter
>>