linux-kernel - Re: [PATCH v2 7/7] kunit, slub: add test_kfree_rcu() and test_leak

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Message-ID: <CAB=+i9SQHqVrfUbuSgsKbD07k37MUsPcU7NMSYgwXhLL+UhF2w@mail.gmail.com>
Date: Sun, 22 Sep 2024 15:16:50 +0900
From: Hyeonggon Yoo <42.hyeyoo@...il.com>
To: Vlastimil Babka <vbabka@...e.cz>
Cc: Guenter Roeck <linux@...ck-us.net>, KUnit Development <kunit-dev@...glegroups.com>, 
	Brendan Higgins <brendanhiggins@...gle.com>, David Gow <davidgow@...gle.com>, 
	"Paul E. McKenney" <paulmck@...nel.org>, Joel Fernandes <joel@...lfernandes.org>, 
	Josh Triplett <josh@...htriplett.org>, Boqun Feng <boqun.feng@...il.com>, 
	Christoph Lameter <cl@...ux.com>, David Rientjes <rientjes@...gle.com>, Steven Rostedt <rostedt@...dmis.org>, 
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>, Lai Jiangshan <jiangshanlai@...il.com>, 
	Zqiang <qiang.zhang1211@...il.com>, Julia Lawall <Julia.Lawall@...ia.fr>, 
	Jakub Kicinski <kuba@...nel.org>, "Jason A. Donenfeld" <Jason@...c4.com>, 
	"Uladzislau Rezki (Sony)" <urezki@...il.com>, Andrew Morton <akpm@...ux-foundation.org>, 
	Roman Gushchin <roman.gushchin@...ux.dev>, linux-mm@...ck.org, linux-kernel@...r.kernel.org, 
	rcu@...r.kernel.org, Alexander Potapenko <glider@...gle.com>, Marco Elver <elver@...gle.com>, 
	Dmitry Vyukov <dvyukov@...gle.com>, kasan-dev@...glegroups.com, 
	Jann Horn <jannh@...gle.com>, Mateusz Guzik <mjguzik@...il.com>
Subject: Re: [PATCH v2 7/7] kunit, slub: add test_kfree_rcu() and test_leak_destroy()

On Sun, Sep 22, 2024 at 6:25 AM Vlastimil Babka <vbabka@...e.cz> wrote:
>
> On 9/21/24 23:08, Guenter Roeck wrote:
> > On 9/21/24 13:40, Vlastimil Babka wrote:
> >> +CC kunit folks
> >>
> >> On 9/20/24 15:35, Guenter Roeck wrote:
> >>> Hi,
> >>
> >> Hi,
> >>
> >>> On Wed, Aug 07, 2024 at 12:31:20PM +0200, Vlastimil Babka wrote:
> >>>> Add a test that will create cache, allocate one object, kfree_rcu() it
> >>>> and attempt to destroy it. As long as the usage of kvfree_rcu_barrier()
> >>>> in kmem_cache_destroy() works correctly, there should be no warnings in
> >>>> dmesg and the test should pass.
> >>>>
> >>>> Additionally add a test_leak_destroy() test that leaks an object on
> >>>> purpose and verifies that kmem_cache_destroy() catches it.
> >>>>
> >>>> Signed-off-by: Vlastimil Babka <vbabka@...e.cz>
> >>>
> >>> This test case, when run, triggers a warning traceback.
> >>>
> >>> kmem_cache_destroy TestSlub_kfree_rcu: Slab cache still has objects when called from test_leak_destroy+0x70/0x11c
> >>> WARNING: CPU: 0 PID: 715 at mm/slab_common.c:511 kmem_cache_destroy+0x1dc/0x1e4
> >>
> >> Yes that should be suppressed like the other slub_kunit tests do. I have
> >> assumed it's not that urgent because for example the KASAN kunit tests all
> >> produce tons of warnings and thus assumed it's in some way acceptable for
> >> kunit tests to do.
> >>
> >
> > I have all tests which generate warning backtraces disabled. Trying to identify
> > which warnings are noise and which warnings are on purpose doesn't scale,
> > so it is all or nothing for me. I tried earlier to introduce a patch series
> > which would enable selective backtrace suppression, but that died the death
> > of architecture maintainers not caring and people demanding it to be perfect
> > (meaning it only addressed WARNING: backtraces and not BUG: backtraces,
> > and apparently that wasn't good enough).
>
> Ah, didn't know, too bad.
>
> > If the backtrace is intentional (and I think you are saying that it is),
> > I'll simply disable the test. That may be a bit counter-productive, but
> > there is really no alternative for me.
>
> It's intentional in the sense that the test intentionally triggers a
> condition that normally produces a warning. Many if the slub kunit test do
> that, but are able to suppress printing the warning when it happens in the
> kunit context. I forgot to do that for the new test initially as the warning
> there happens from a different path that those that already have the kunit
> suppression, but we'll implement that suppression there too ASAP.

We might also need to address the concern of the commit
7302e91f39a ("mm/slab_common: use WARN() if cache still has objects on
destroy"),
the concern that some users prefer WARN() over pr_err() to catch
errors on testing systems
which relies on WARN() format, and to respect panic_on_warn.

So we might need to call WARN() instead of pr_err() if there are errors in
slub error handling code in general, except when running kunit tests?

Thanks,
Hyeonggon