Re: [RFC PATCH 2/2] KUnit: KASAN Integration

From: Dmitry Vyukov <dvyukov@google.com>
To: Patricia Alfonso <trishalfonso@google.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>,
	Brendan Higgins <brendanhiggins@google.com>,
	David Gow <davidgow@google.com>, Ingo Molnar <mingo@redhat.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Juri Lelli <juri.lelli@redhat.com>,
	Vincent Guittot <vincent.guittot@linaro.org>,
	LKML <linux-kernel@vger.kernel.org>,
	kasan-dev <kasan-dev@googlegroups.com>,
	"open list:KERNEL SELFTEST FRAMEWORK" 
	<linux-kselftest@vger.kernel.org>,
	kunit-dev@googlegroups.com
Subject: Re: [RFC PATCH 2/2] KUnit: KASAN Integration
Date: Wed, 4 Mar 2020 07:23:41 +0100	[thread overview]
Message-ID: <CACT4Y+b5WaH8OkAJCDeAJcYQ1cbnbqgiF=tTb7CCmtY4UXHc0A@mail.gmail.com> (raw)
In-Reply-To: <CAKFsvU+ruKWt-BdVz+OX-T9wNEBetqVFACsG1B9ucMS4zHrMBQ@mail.gmail.com>

On Wed, Mar 4, 2020 at 2:26 AM Patricia Alfonso <trishalfonso@google.com> wrote:
>
> On Sat, Feb 29, 2020 at 10:29 PM Dmitry Vyukov <dvyukov@google.com> wrote:
> >
> > On Sat, Feb 29, 2020 at 2:23 AM Patricia Alfonso
> > <trishalfonso@google.com> wrote:
> > > >
> > > > On Thu, Feb 27, 2020 at 3:44 AM 'Patricia Alfonso' via kasan-dev
> > > > <kasan-dev@googlegroups.com> wrote:
> > > > >
> > > > > --- a/tools/testing/kunit/kunit_kernel.py
> > > > > +++ b/tools/testing/kunit/kunit_kernel.py
> > > > > @@ -141,7 +141,7 @@ class LinuxSourceTree(object):
> > > > >                 return True
> > > > >
> > > > >         def run_kernel(self, args=[], timeout=None, build_dir=''):
> > > > > -               args.extend(['mem=256M'])
> > > > > +               args.extend(['mem=256M', 'kasan_multi_shot'])
> > > >
> > > > This is better done somewhere else (different default value if
> > > > KASAN_TEST is enabled or something). Or overridden in the KASAN tests.
> > > > Not everybody uses tools/testing/kunit/kunit_kernel.py and this seems
> > > > to be a mandatory part now. This means people will always hit this, be
> > > > confused, figure out they need to flip the value, and only then be
> > > > able to run kunit+kasan.
> > > >
> > > I agree. Is the best way to do this with "bool multishot =
> > > kasan_save_enable_multi_shot();"  and
> > > "kasan_restore_multi_shot(multishot);" inside test_kasan.c like what
> > > was done in the tests before?
> >
> > This will fix KASAN tests, but not non-KASAN tests running under KUNIT
> > and triggering KASAN reports.
> > You set kasan_multi_shot for all KUNIT tests. I am reading this as
> > that we don't want to abort on the first test that triggered a KASAN
> > report. Or not?
>
> I don't think I understand the question, but let me try to explain my
> thinking and see if that resonates with you. We know that the KASAN
> tests will require more than one report, and we want that. For most
> users, since a KASAN error can cause unexpected kernel behavior for
> anything after a KASAN error, it is best for just one unexpected KASAN
> error to be the only error printed to the user, unless they specify
> kasan-multi-shot. The way I understand it, the way to implement this
> is to use  "bool multishot = kasan_save_enable_multi_shot();"  and
> "kasan_restore_multi_shot(multishot);" around the KASAN tests so that
> kasan-multi-shot is temporarily enabled for the tests we expect
> multiple reports. I assume "kasan_restore_multi_shot(multishot);"
> restores the value to what the user input was so after the KASAN tests
> are finished, if the user did not specify kasan-multi-shot and an
> unexpected kasan error is reported, it will print the full report and
> only that first one. Is this understanding correct? If you have a
> better way of implementing this or a better expected behavior, I
> appreciate your thoughts.

Everything you say is correct.
What I tried to point at is that this new behavior is different from
the original behavior of your change. Initially you added
kasan_multi_shot to command line for _all_ kunit tests (not just
KASAN). The question is: do we want kasan_multi_shot for non-KASAN
tests or not?