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From:   Brendan Higgins <brendanhiggins@google.com>
Date:   Mon, 10 Aug 2020 13:35:35 -0700
Message-ID: <CAFd5g46=zgY_+jawXMS+yTx6MhRGa_4-WVmer-BwoL_c2QPcrg@mail.gmail.com>
Subject: Re: [PATCH] kunit: added lockdep support
To:     Uriel Guajardo <urielguajardo@google.com>
Cc:     Uriel Guajardo <urielguajardojr@gmail.com>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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On Thu, Aug 6, 2020 at 1:43 PM Uriel Guajardo <urielguajardo@google.com> wrote:
>
> On Thu, Aug 6, 2020 at 3:37 PM Uriel Guajardo <urielguajardojr@gmail.com> wrote:
> >
> > From: Uriel Guajardo <urielguajardo@google.com>
> >
> > KUnit tests will now fail if lockdep detects an error during a test
> > case.
> >
> > The idea comes from how lib/locking-selftest [1] checks for lock errors: we
> > first if lock debugging is turned on. If not, an error must have
> > occurred, so we fail the test and restart lockdep for the next test case.
> >
> > Like the locking selftests, we also fix possible preemption count
> > corruption from lock bugs.

Sorry, just noticed: You probably want to send this to some of the
lockdep maintainers or the maintainers of the kselftest for lockdep.

> > Depends on kunit: support failure from dynamic analysis tools [2]
> >
> > [1] https://elixir.bootlin.com/linux/v5.7.12/source/lib/locking-selftest.c#L1137
> >
> > [2] https://lore.kernel.org/linux-kselftest/20200806174326.3577537-1-urielguajardojr@gmail.com/
> >
> > Signed-off-by: Uriel Guajardo <urielguajardo@google.com>
> > ---
> >  lib/kunit/test.c | 26 +++++++++++++++++++++++++-
> >  1 file changed, 25 insertions(+), 1 deletion(-)
> >
> > diff --git a/lib/kunit/test.c b/lib/kunit/test.c
> > index d8189d827368..0838ececa005 100644
> > --- a/lib/kunit/test.c
> > +++ b/lib/kunit/test.c
> > @@ -11,6 +11,8 @@
> >  #include <linux/kref.h>
> >  #include <linux/sched/debug.h>
> >  #include <linux/sched.h>
> > +#include <linux/lockdep.h>
> > +#include <linux/debug_locks.h>
> >
> >  #include "debugfs.h"
> >  #include "string-stream.h"
> > @@ -22,6 +24,26 @@ void kunit_fail_current_test(void)
> >                 kunit_set_failure(current->kunit_test);
> >  }
> >
> > +static inline void kunit_check_locking_bugs(struct kunit *test,
> > +                                           unsigned long 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
>
> I am not entirely sure why lib/locking-selftests enables/disables
> softirqs, but I suspect it has to do with the fact that preempt_count
> became corrupted, and somehow softirqs became incorrectly
> enabled/disabled as a result. The resetting of the preemption count
> will undo the enabling/disabling accordingly. Any insight on this
> would be appreciated!
>
> > +#if IS_ENABLED(CONFIG_LOCKDEP)
> > +       local_irq_disable();
> > +       if (!debug_locks) {
> > +               kunit_set_failure(test);
> > +               lockdep_reset();
> > +       }
> > +       local_irq_enable();
> > +#endif
> > +}
> > +
> >  static void kunit_print_tap_version(void)
> >  {
> >         static bool kunit_has_printed_tap_version;
> > @@ -289,6 +311,7 @@ static void kunit_try_run_case(void *data)
> >         struct kunit *test = ctx->test;
> >         struct kunit_suite *suite = ctx->suite;
> >         struct kunit_case *test_case = ctx->test_case;
> > +       unsigned long saved_preempt_count = preempt_count();
> >
> >         current->kunit_test = test;
> >
> > @@ -298,7 +321,8 @@ static void kunit_try_run_case(void *data)
> >          * thread will resume control and handle any necessary clean up.
> >          */
> >         kunit_run_case_internal(test, suite, test_case);
> > -       /* This line may never be reached. */
> > +       /* These lines may never be reached. */
> > +       kunit_check_locking_bugs(test, saved_preempt_count);
> >         kunit_run_case_cleanup(test, suite);
> >  }
> >
> > --
> > 2.28.0.236.gb10cc79966-goog
> >