linux-kernel - Re: [PATCH slab hotfixes v2 2/2] slub/kunit: skip test_kfree

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Message-ID: <7f18cd71-4a4a-4d29-beb4-33f6d9fe3c12@suse.cz>
Date: Wed, 2 Oct 2024 16:44:45 +0200
From: Vlastimil Babka <vbabka@...e.cz>
To: Guenter Roeck <linux@...ck-us.net>, Christoph Lameter <cl@...ux.com>,
 David Rientjes <rientjes@...gle.com>
Cc: Roman Gushchin <roman.gushchin@...ux.dev>,
 Andrew Morton <akpm@...ux-foundation.org>,
 Hyeonggon Yoo <42.hyeyoo@...il.com>, linux-kernel@...r.kernel.org,
 linux-mm@...ck.org, "Paul E. McKenney" <paulmck@...nel.org>,
 Boqun Feng <boqun.feng@...il.com>, Uladzislau Rezki <urezki@...il.com>,
 rcu@...r.kernel.org, David Gow <davidgow@...gle.com>,
 Rae Moar <rmoar@...gle.com>, linux-kselftest@...r.kernel.org,
 kunit-dev@...glegroups.com, Brendan Higgins <brendan.higgins@...ux.dev>
Subject: Re: [PATCH slab hotfixes v2 2/2] slub/kunit: skip test_kfree_rcu when
 the slub kunit test is built-in

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@...ck-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.

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