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

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

[ Adding more interested parties]

On Wed, Mar 20, 2024 at 09:23:24AM -0700, 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,
> Guenter