Re: [PATCH slab hotfixes v2 2/2] slub/kunit: skip test_kfree_rcu when the slub kunit test is built-in

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

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On 10/2/24 03:26, Vlastimil Babka wrote:
> On 10/1/24 18:20, Vlastimil Babka wrote:
>> Guenter Roeck reports that the new slub kunit tests added by commit
>> 4e1c44b3db79 ("kunit, slub: add test_kfree_rcu() and
>> test_leak_destroy()") cause a lockup on boot on several architectures
>> when the kunit tests are configured to be built-in and not modules.
>>
>> The test_kfree_rcu test invokes kfree_rcu() and boot sequence inspection
>> showed the runner for built-in kunit tests kunit_run_all_tests() is
>> called before setting system_state to SYSTEM_RUNNING and calling
>> rcu_end_inkernel_boot(), so this seems like a likely cause. So while I
>> was unable to reproduce the problem myself, skipping the test when the
>> slub_kunit module is built-in should avoid the issue.
>>
>> An alternative fix that was moving the call to kunit_run_all_tests() a
>> bit later in the boot was tried, but has broken tests with functions
>> marked as __init due to free_initmem() already being done.
>>
>> Fixes: 4e1c44b3db79 ("kunit, slub: add test_kfree_rcu() and test_leak_destroy()")
>> Reported-by: Guenter Roeck <linux@roeck-us.net>
>> Closes: https://lore.kernel.org/all/6fcb1252-7990-4f0d-8027-5e83f0fb9409@roeck-us.net/
> 
> I hope you can confirm it helps, because the commit added two tests and I've
> only skipped one of them, as it's the one using kfree_rcu(), which is
> suspected. But the other is responsible for the (now suppressed)
> kmem_cache_destroy() warning, and maybe I'm missing something and it was
> actually that one causing the lockups.
> 

Everything works with your patches applied, so we are good.

> Since you mentioned the boot lockups happened on some x86_64 too, do you
> have a .config of the lockup case? I've tried tweaking some rcu options but
> still nothing.
> 

I have a bunch of debug options enabled. Configuration (generated using
"make savedefconfig") for x86_64 is attached.

Thanks,
Guenter

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