linux-kernel - Re: [PATCH v3] kunit: added lockdep support

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Date:   Sat, 15 Aug 2020 11:17:21 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Uriel Guajardo <urielguajardojr@...il.com>,
        brendanhiggins@...gle.com, mingo@...hat.com, will@...nel.org,
        linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
        kunit-dev@...glegroups.com, urielguajardo@...gle.com,
        alan.maguire@...cle.com
Subject: Re: [PATCH v3] kunit: added lockdep support


* Peter Zijlstra <peterz@...radead.org> wrote:

> On Sat, Aug 15, 2020 at 10:30:29AM +0200, Ingo Molnar wrote:
> > 
> > * Uriel Guajardo <urielguajardojr@...il.com> wrote:
> > 
> > > From: Uriel Guajardo <urielguajardo@...gle.com>
> > > 
> > > KUnit will fail tests upon observing a lockdep failure. Because lockdep
> > > turns itself off after its first failure, only fail the first test and
> > > warn users to not expect any future failures from lockdep.
> > > 
> > > Similar to lib/locking-selftest [1], we check if the status of
> > > debug_locks has changed after the execution of a test case. However, we
> > > do not reset lockdep afterwards.
> > > 
> > > Like the locking selftests, we also fix possible preemption count
> > > corruption from lock bugs.
> > 
> > > --- a/lib/kunit/Makefile
> > > +++ b/lib/kunit/Makefile
> > 
> > > +void kunit_check_lockdep(struct kunit *test, struct kunit_lockdep *lockdep) {
> > > +	int saved_preempt_count = lockdep->preempt_count;
> > > +	bool saved_debug_locks = lockdep->debug_locks;
> > > +
> > > +	if (DEBUG_LOCKS_WARN_ON(preempt_count() != saved_preempt_count))
> > > +		preempt_count_set(saved_preempt_count);
> > > +
> > > +#ifdef CONFIG_TRACE_IRQFLAGS
> > > +	if (softirq_count())
> > > +		current->softirqs_enabled = 0;
> > > +	else
> > > +		current->softirqs_enabled = 1;
> > > +#endif
> > > +
> > > +	if (saved_debug_locks && !debug_locks) {
> > > +		kunit_set_failure(test);
> > > +		kunit_warn(test, "Dynamic analysis tool failure from LOCKDEP.");
> > > +		kunit_warn(test, "Further tests will have LOCKDEP disabled.");
> > > +	}
> > 
> > 
> > So this basically duplicates what the boot-time locking self-tests do, 
> > in a poor fashion?
> 
> No, it makes sure that any kunit based self-test fails when it messes up
> it's locking.

We have a flag for whether lockdep is running though, so is this 
basically a very complicated way to parse /proc/lockdep_debug? :-)

Thanks,

	Ingo