linux-kernel - Re: [PATCH 0/2] mm: Two small fixes for recent syzbot reports

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Date:   Wed, 15 Apr 2020 13:09:32 +0200
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Dan Rue <dan.rue@...aro.org>
Cc:     Qian Cai <cai@....pw>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Peter Xu <peterx@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>, Jens Axboe <axboe@...nel.dk>,
        Christoph Lameter <cl@...ux.com>,
        Johannes Weiner <hannes@...xchg.org>,
        syzkaller <syzkaller@...glegroups.com>
Subject: Re: [PATCH 0/2] mm: Two small fixes for recent syzbot reports

On Tue, Apr 14, 2020 at 9:28 PM Dan Rue <dan.rue@...aro.org> wrote:
>
> On Tue, Apr 14, 2020 at 01:12:50PM +0200, Dmitry Vyukov wrote:
> > On Tue, Apr 14, 2020 at 12:06 AM Qian Cai <cai@....pw> wrote:
> > > Well, there are other CI's beyond syzbot.
> > > On the other hand, this makes me worry who is testing on linux-next every day.
> >
> > How do these use-after-free's and locking bugs get past the
> > unit-testing systems (which syzbot is not) and remain unnoticed for so
> > long?...
> > syzbot uses the dumbest VMs (GCE), so everything it triggers during
> > boot should be triggerable pretty much everywhere.
> > It seems to be an action point for the testing systems. "Boot to ssh"
> > is not the best criteria. Again if there is a LOCKDEP error, we are
> > not catching any more LOCKDEP errors during subsequent testing. If
> > there is a use-after-free, that's a serious error on its own and KASAN
> > produces only 1 error by default as well. And as far as I understand,
> > lots of kernel testing systems don't even enable KASAN, which is very
> > wrong.
> > I've talked to +Dan Rue re this few days ago. Hopefully LKFT will
> > start catching these as part of unit testing. Which should help with
> > syzbot testing as well.
>
> LKFT has recently added testing with KASAN enabled and improved the
> kernel log parsing to catch more of this class of errors while
> performing our regular functional testing.
>
> Incidentally, -next was also broken for us from March 25 through April 5
> due to a perf build failure[0], which eventually made itself all the way
> down into v5.6 release and I believe the first two 5.6.x stable
> releases.
>
> For -next, LKFT's gap is primarily reporting. We do build and run over
> 30k tests on every -next daily release, but we send out issues manually
> when we see them because triaging is still a manual effort. We're
> working to build better automated reporting. If anyone is interested in
> watching LKFT's -next results more closely (warning, it's a bit noisy),
> please let me know. Watching the results at https://lkft.linaro.org
> provides some overall health indications, but again, it gets pretty
> difficult to figure out signal from noise once you start drilling down
> without sufficient context of the system.

What kind of failures and noise do you get? Is it flaky tests?
I would assume build failures are ~0% flaky/noisy. And boot failures
are maybe ~1% flaky/noisy due to some infra issues.

I can't find any actual test failure logs in the UI. I've got to this page:
https://qa-reports.linaro.org/lkft/linux-mainline-oe/build/v5.7-rc1-24-g8632e9b5645b/testrun/1363280/suite/kselftest/tests/
which seem to contain failed tests on mainline. But I still can't find
the actual test failure logs.


> Dan
>
> [0] https://lore.kernel.org/stable/CA+G9fYsZjmf34pQT1DeLN_DDwvxCWEkbzBfF0q2VERHb25dfZQ@mail.gmail.com/
>
> --
> Linaro LKFT
> https://lkft.linaro.org