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

[Vlastimil Babka]

On 10/2/24 15:52, Guenter Roeck wrote:
> 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@xxxxxxxxxxxx>
>>> Closes: https://lore.kernel.org/all/6fcb1252-7990-4f0d-8027-5e83f0fb9409@xxxxxxxxxxxx/
>> 
>> 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.

Thanks for testing! Queued for -next now and will send to Linus later if
all's 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.

Hmm, didn't see the hang with that (using virtme-ng) on v6.12-rc1. Guess
there's something more to it. Oh well.

> Thanks,
> Guenter