linux-kernel - Re: [PATCH v2] kunit: added lockdep support

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Message-ID: <20200813103615.GT2674@hirez.programming.kicks-ass.net>
Date:   Thu, 13 Aug 2020 12:36:15 +0200
From:   peterz@...radead.org
To:     Uriel Guajardo <urielguajardojr@...il.com>
Cc:     brendanhiggins@...gle.com, mingo@...hat.com, will@...nel.org,
        linux-kselftest@...r.kernel.org, kunit-dev@...glegroups.com,
        linux-kernel@...r.kernel.org, urielguajardo@...gle.com
Subject: Re: [PATCH v2] kunit: added lockdep support

On Wed, Aug 12, 2020 at 07:33:32PM +0000, Uriel Guajardo wrote:
> 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.

> +static void kunit_check_locking_bugs(struct kunit *test,
> +				     unsigned long saved_preempt_count,
> +				     bool saved_debug_locks)
> +{
> +	preempt_count_set(saved_preempt_count);
> +#ifdef CONFIG_TRACE_IRQFLAGS
> +	if (softirq_count())
> +		current->softirqs_enabled = 0;
> +	else
> +		current->softirqs_enabled = 1;
> +#endif

Urgh, don't silently change these... if they're off that's a hard fail.

	if (DEBUG_LOCKS_WARN_ON(preempt_count() != saved_preempt_count))
		preempt_count_set(saved_preempt_count);

And by using DEBUG_LOCKS_WARN_ON() it will kill IRQ tracing and trigger
the below fail.

> +	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.");
> +	}
> +}