linux-kernel - Re: INFO: rcu detected stall in sys

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Date:   Tue, 14 Jan 2020 11:15:26 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Alexander Potapenko <glider@...gle.com>
Cc:     Nick Desaulniers <ndesaulniers@...gle.com>,
        Casey Schaufler <casey@...aufler-ca.com>,
        Daniel Axtens <dja@...ens.net>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        syzbot <syzbot+de8d933e7d153aa0c1bb@...kaller.appspotmail.com>,
        kasan-dev <kasan-dev@...glegroups.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>
Subject: Re: INFO: rcu detected stall in sys_kill

The clang instances are back to life (incl smack).

#syz invalid

On Fri, Jan 10, 2020 at 9:37 AM 'Alexander Potapenko' via kasan-dev
<kasan-dev@...glegroups.com> wrote:
>
> On Thu, Jan 9, 2020 at 6:39 PM 'Nick Desaulniers' via kasan-dev
> <kasan-dev@...glegroups.com> wrote:
> >
> > On Thu, Jan 9, 2020 at 9:23 AM Dmitry Vyukov <dvyukov@...gle.com> wrote:
> > >
> > > On Thu, Jan 9, 2020 at 6:17 PM Nick Desaulniers <ndesaulniers@...gle.com> wrote:
> > > > I disabled loop unrolling and loop unswitching in LLVM when the loop
> > > > contained asm goto in:
> > > > https://github.com/llvm/llvm-project/commit/c4f245b40aad7e8627b37a8bf1bdcdbcd541e665
> > > > I have a fix for loop unrolling in:
> > > > https://reviews.llvm.org/D64101
> > > > that I should dust off. I haven't looked into loop unswitching yet.
> > >
> > > c4f245b40aad7e8627b37a8bf1bdcdbcd541e665 is in the range between the
> > > broken compiler and the newer compiler that seems to work, so I would
> > > assume that that commit fixes this.
> > > We will get the final stamp from syzbot hopefully by tomorrow.
> >
> > How often do you refresh the build of Clang in syzbot? Is it manual? I
> > understand the tradeoffs of living on the tip of the spear, but
> > c4f245b40aad7e8627b37a8bf1bdcdbcd541e665 is 6 months old.  So upstream
> > LLVM could be regressing more often, and you wouldn't notice for 1/2 a
> > year or more. :-/
> KMSAN used to be the only user of Clang on syzbot, so I didn't bother too often.
> Now that there are other users, we'll need a better strategy.
> Clang revisions I've been picking previously came from Chromium's
> Clang distributions. This is nice, because Chromium folks usually pick
> a revision that has been extensively tested at Google already, plus
> they make sure Chromium tests also pass.
> They don't roll the compiler often, however (typically once a month or
> two, but this time there were holidays, plus some nasty breakages).
> > --
> > Thanks,
> > ~Nick Desaulniers
> >
> > --
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>
>
>
> --
> Alexander Potapenko
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>
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