netdev - Re: lock warnings in dev_addr

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Message-ID: <228845bb-1a90-42eb-b2d7-47007734535e@roeck-us.net>
Date: Thu, 29 Feb 2024 12:34:20 -0800
From: Guenter Roeck <linux@...ck-us.net>
To: David Gow <davidgow@...gle.com>
Cc: Jakub Kicinski <kuba@...nel.org>, Eric Dumazet <edumazet@...gle.com>,
 netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
 Brendan Higgins <brendanhiggins@...gle.com>,
 linux-kselftest@...r.kernel.org, kunit-dev@...glegroups.com
Subject: Re: lock warnings in dev_addr_lists test

On 2/29/24 00:10, David Gow wrote:
> On Thu, 29 Feb 2024 at 03:45, Guenter Roeck <linux@...ck-us.net> wrote:
>>
>> Hi,
>>
>> when running the dev_addr_lists unit test with lock debugging enabled,
>> I always get the following lockdep warning.
>>
>> [    7.031327] ====================================
>> [    7.031393] WARNING: kunit_try_catch/1886 still has locks held!
>> [    7.031478] 6.8.0-rc6-00053-g0fec7343edb5-dirty #1 Tainted: G        W        N
>> [    7.031728] ------------------------------------
>> [    7.031816] 1 lock held by kunit_try_catch/1886:
>> [    7.031896]  #0: ffffffff8ed35008 (rtnl_mutex){+.+.}-{3:3}, at: dev_addr_test_init+0x6a/0x100
>>
>> Instrumentation shows that dev_addr_test_exit() is called, but only
>> after the warning fires.
>>
>> Is this a problem with kunit tests or a problem with this specific test ?
> 
> A bit of both, I think. KUnit test cleanup is not guaranteed to run in
> the same thread as the test, so that definitely is triggering lockdep
> warnings.
> 
> On the other hand, we really should make this particular case work in
> KUnit. Ideally test cleanup will happen on the test thread first, and
> only fall back to another test if the test thread otherwise aborted.
> 
> So, this is probably something we won't be able to fix if the test
> fails, but it definitely shouldn't be happening here where it passes.
> I'll look into fixing that.
> 

Other tests seem to have similar problems with locking:

[   25.762445]         # Subtest: drm_vc4_test_pv_muxing
[   25.845857] [drm] Initialized vc4 0.0.0 20140616 for drm_vc4_test_pv_muxing.drm-kunit-mock-device on minor 0
[   25.859603]
[   25.859867] ====================================
[   25.860085] WARNING: kunit_try_catch/1729 still has locks held!
[   25.860354] 6.8.0-rc6-00066-g1c8c39f56e47-dirty #1 Tainted: G        W        N
[   25.860675] ------------------------------------
[   25.860918] 2 locks held by kunit_try_catch/1729:
[   25.865468]  #0: ffff17e04945d850 (crtc_ww_class_acquire){+.+.}-{0:0}, at: drm_kunit_helper_acquire_ctx_alloc+0x44/0xd4
[   25.866383]  #1: ffff17e047042518 (crtc_ww_class_mutex){+.+.}-{3:3}, at: modeset_lock.part.0+0x134/0x1d0

Guenter