linux-ext4 - Re: [PATCH v2 2/5] ext4: Add unit test of ext4_mb_generate

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Date: Wed, 20 Mar 2024 09:23:22 -0700
From: Guenter Roeck <linux@...ck-us.net>
To: Kemeng Shi <shikemeng@...weicloud.com>
Cc: tytso@....edu, adilger.kernel@...ger.ca, linux-ext4@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/5] ext4: Add unit test of ext4_mb_generate_buddy

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@...weicloud.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,
Guenter