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Message-ID: <CAFd5g44BfUxyS=wxFCWFeD4PYBcmyKa_GaODajS8nc6JZ9OADA@mail.gmail.com>
Date: Fri, 9 Apr 2021 00:54:38 -0700
From: Brendan Higgins <brendanhiggins@...gle.com>
To: Daniel Latypov <dlatypov@...gle.com>
Cc: Marco Elver <elver@...gle.com>, Vlastimil Babka <vbabka@...e.cz>,
glittao@...il.com, Christoph Lameter <cl@...ux.com>,
Pekka Enberg <penberg@...nel.org>,
David Rientjes <rientjes@...gle.com>,
Joonsoo Kim <iamjoonsoo.kim@....com>,
Andrew Morton <akpm@...ux-foundation.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Linux Memory Management List <linux-mm@...ck.org>,
KUnit Development <kunit-dev@...glegroups.com>,
David Gow <davidgow@...gle.com>
Subject: Re: [PATCH v3 1/2] kunit: add a KUnit test for SLUB debugging functionality
On Thu, Apr 8, 2021 at 10:19 AM Daniel Latypov <dlatypov@...gle.com> wrote:
>
> On Thu, Apr 8, 2021 at 3:30 AM Marco Elver <elver@...gle.com> wrote:
> >
> > On Tue, 6 Apr 2021 at 12:57, Vlastimil Babka <vbabka@...e.cz> wrote:
> > >
> > >
> > > On 4/1/21 11:24 PM, Marco Elver wrote:
> > > > On Thu, 1 Apr 2021 at 21:04, Daniel Latypov <dlatypov@...gle.com> 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 <vbabka@...e.cz>
> > > 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))
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