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Fri, 09 Apr 2021 00:54:49 -0700 (PDT) MIME-Version: 1.0 References: <20210331085156.5028-1-glittao@gmail.com> <11886d4f-8826-0cd6-b5fd-defc65470ed5@suse.cz> In-Reply-To: From: Brendan Higgins Date: Fri, 9 Apr 2021 00:54:38 -0700 Message-ID: Subject: Re: [PATCH v3 1/2] kunit: add a KUnit test for SLUB debugging functionality To: Daniel Latypov Cc: Marco Elver , Vlastimil Babka , glittao@gmail.com, Christoph Lameter , Pekka Enberg , David Rientjes , Joonsoo Kim , Andrew Morton , Linux Kernel Mailing List , Linux Memory Management List , KUnit Development , David Gow Content-Type: text/plain; charset="UTF-8" X-Rspamd-Queue-Id: 13A6FC0001EE X-Stat-Signature: 4tgypqtjwzd9kam8a97oeekci9skkqnz X-Rspamd-Server: rspam02 Received-SPF: none (google.com>: No applicable sender policy available) receiver=imf14; identity=mailfrom; envelope-from=""; helo=mail-pj1-f48.google.com; client-ip=209.85.216.48 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1617954884-500416 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Thu, Apr 8, 2021 at 10:19 AM Daniel Latypov wrote: > > On Thu, Apr 8, 2021 at 3:30 AM Marco Elver wrote: > > > > On Tue, 6 Apr 2021 at 12:57, Vlastimil Babka wrote: > > > > > > > > > On 4/1/21 11:24 PM, Marco Elver wrote: > > > > On Thu, 1 Apr 2021 at 21:04, Daniel Latypov wrote: > > > >> > } > > > >> > #else > > > >> > static inline bool slab_add_kunit_errors(void) { return false; } > > > >> > #endif > > > >> > > > > >> > And anywhere you want to increase the error count, you'd call > > > >> > slab_add_kunit_errors(). > > > >> > > > > >> > Another benefit of this approach is that if KUnit is disabled, there is > > > >> > zero overhead and no additional code generated (vs. the current > > > >> > approach). > > > >> > > > >> The resource approach looks really good, but... > > > >> You'd be picking up a dependency on > > > >> https://lore.kernel.org/linux-kselftest/20210311152314.3814916-2-dlatypov@google.com/ > > > >> current->kunit_test will always be NULL unless CONFIG_KASAN=y && > > > >> CONFIG_KUNIT=y at the moment. > > > >> My patch drops the CONFIG_KASAN requirement and opens it up to all tests. > > > > > > > > Oh, that's a shame, but hopefully it'll be in -next soon. > > > > > > > >> At the moment, it's just waiting another look over from Brendan or David. > > > >> Any ETA on that, folks? :) > > > >> > > > >> So if you don't want to get blocked on that for now, I think it's fine to add: > > > >> #ifdef CONFIG_SLUB_KUNIT_TEST > > > >> int errors; > > > >> #endif > > > > > > > > Until kunit fixes setting current->kunit_test, a cleaner workaround > > > > that would allow to do the patch with kunit_resource, is to just have > > > > an .init/.exit function that sets it ("current->kunit_test = test;"). > > > > And then perhaps add a note ("FIXME: ...") to remove it once the above > > > > patch has landed. > > > > > > > > At least that way we get the least intrusive change for mm/slub.c, and > > > > the test is the only thing that needs a 2-line patch to clean up > > > > later. > > > > > > So when testing internally Oliver's new version with your suggestions (thanks > > > again for those), I got lockdep splats because slab_add_kunit_errors is called > > > also from irq disabled contexts, and kunit_find_named_resource will call > > > spin_lock(&test->lock) that's not irq safe. Can we make the lock irq safe? I > > > tried the change below and it makde the problem go away. If you agree, the > > > question is how to proceed - make it part of Oliver's patch series and let > > > Andrew pick it all with eventually kunit team's acks on this patch, or whatnot. > > > > From what I can tell it should be fine to make it irq safe (ack for > > your patch below). Regarding patch logistics, I'd probably add it to > > the series. If that ends up not working, we'll find out sooner or > > later. > > > > (FYI, the prerequisite patch for current->kunit_test is in -next now.) > > Yep. > There's also two follow-up patches in > https://git.kernel.org/pub/scm/linux/kernel/git/shuah/linux-kselftest.git/log/?h=kunit > > > > > KUnit maintainers, do you have any preferences? > > Poked offline and Brendan and David seemed fine either way. > So probably just include it in this patch series for convenience. > > Brendan also mentioned KUnit used to use spin_lock_irqsave/restore() > but had been told to not use it until necessary. > See https://lore.kernel.org/linux-kselftest/20181016235120.138227-3-brendanhiggins@google.com/ > So I think there's no objections to the patch itself either. > > But I'd wait for Brendan to chime in to confirm. That's correct. Before KUnit was accepted upstream, early versions of the patchset used the irqsave/restore versions. I was asked to remove them until they were necessary, and it looks like that time is now :-) So yes, I would be happy to see this patch go in. Looks good to me the way you have it below. Send it out as its own patch in your series and I will give it a Reviewed-by. Thanks! > > > ----8<---- > > > > > > commit ab28505477892e9824c57ac338c88aec2ec0abce > > > Author: Vlastimil Babka > > > Date: Tue Apr 6 12:28:07 2021 +0200 > > > > > > kunit: make test->lock irq safe > > > > > > diff --git a/include/kunit/test.h b/include/kunit/test.h > > > index 49601c4b98b8..524d4789af22 100644 > > > --- a/include/kunit/test.h > > > +++ b/include/kunit/test.h > > > @@ -515,8 +515,9 @@ kunit_find_resource(struct kunit *test, > > > void *match_data) > > > { > > > struct kunit_resource *res, *found = NULL; > > > + unsigned long flags; > > > > > > - spin_lock(&test->lock); > > > + spin_lock_irqsave(&test->lock, flags); > > > > > > list_for_each_entry_reverse(res, &test->resources, node) { > > > if (match(test, res, (void *)match_data)) { > > > @@ -526,7 +527,7 @@ kunit_find_resource(struct kunit *test, > > > } > > > } > > > > > > - spin_unlock(&test->lock); > > > + spin_unlock_irqrestore(&test->lock, flags); > > > > > > return found; > > > } > > > diff --git a/lib/kunit/test.c b/lib/kunit/test.c > > > index ec9494e914ef..2c62eeb45b82 100644 > > > --- a/lib/kunit/test.c > > > +++ b/lib/kunit/test.c > > > @@ -442,6 +442,7 @@ int kunit_add_resource(struct kunit *test, > > > void *data) > > > { > > > int ret = 0; > > > + unsigned long flags; > > > > > > res->free = free; > > > kref_init(&res->refcount); > > > @@ -454,10 +455,10 @@ int kunit_add_resource(struct kunit *test, > > > res->data = data; > > > } > > > > > > - spin_lock(&test->lock); > > > + spin_lock_irqsave(&test->lock, flags); > > > list_add_tail(&res->node, &test->resources); > > > /* refcount for list is established by kref_init() */ > > > - spin_unlock(&test->lock); > > > + spin_unlock_irqrestore(&test->lock, flags); > > > > > > return ret; > > > } > > > @@ -515,9 +516,11 @@ EXPORT_SYMBOL_GPL(kunit_alloc_and_get_resource); > > > > > > void kunit_remove_resource(struct kunit *test, struct kunit_resource *res) > > > { > > > - spin_lock(&test->lock); > > > + unsigned long flags; > > > + > > > + spin_lock_irqsave(&test->lock, flags); > > > list_del(&res->node); > > > - spin_unlock(&test->lock); > > > + spin_unlock_irqrestore(&test->lock, flags); > > > kunit_put_resource(res); > > > } > > > EXPORT_SYMBOL_GPL(kunit_remove_resource); > > > @@ -597,6 +600,7 @@ EXPORT_SYMBOL_GPL(kunit_kfree); > > > void kunit_cleanup(struct kunit *test) > > > { > > > struct kunit_resource *res; > > > + unsigned long flags; > > > > > > /* > > > * test->resources is a stack - each allocation must be freed in the > > > @@ -608,9 +612,9 @@ void kunit_cleanup(struct kunit *test) > > > * protect against the current node being deleted, not the next. > > > */ > > > while (true) { > > > - spin_lock(&test->lock); > > > + spin_lock_irqsave(&test->lock, flags); > > > if (list_empty(&test->resources)) { > > > - spin_unlock(&test->lock); > > > + spin_unlock_irqrestore(&test->lock, flags); > > > break; > > > } > > > res = list_last_entry(&test->resources, > > > @@ -621,7 +625,7 @@ void kunit_cleanup(struct kunit *test) > > > * resource, and this can't happen if the test->lock > > > * is held. > > > */ > > > - spin_unlock(&test->lock); > > > + spin_unlock_irqrestore(&test->lock, flags); > > > kunit_remove_resource(test, res); > > > } > > > #if (IS_ENABLED(CONFIG_KASAN) && IS_ENABLED(CONFIG_KUNIT))