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From:   Nick Desaulniers <ndesaulniers@google.com>
Date:   Thu, 9 Jan 2020 09:38:52 -0800
Message-ID: <CAKwvOdkh8CV0pgqqHXknv8+gE2ovoKEV_m+qiEmWutmLnra3=g@mail.gmail.com>
Subject: Re: INFO: rcu detected stall in sys_kill
To:     Dmitry Vyukov <dvyukov@google.com>
Cc:     Alexander Potapenko <glider@google.com>,
        Casey Schaufler <casey@schaufler-ca.com>,
        Daniel Axtens <dja@axtens.net>,
        clang-built-linux <clang-built-linux@googlegroups.com>,
        Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>,
        syzbot <syzbot+de8d933e7d153aa0c1bb@syzkaller.appspotmail.com>,
        kasan-dev <kasan-dev@googlegroups.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        LKML <linux-kernel@vger.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@googlegroups.com>
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On Thu, Jan 9, 2020 at 9:23 AM Dmitry Vyukov <dvyukov@google.com> wrote:
>
> On Thu, Jan 9, 2020 at 6:17 PM Nick Desaulniers <ndesaulniers@google.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. :-/

-- 
Thanks,
~Nick Desaulniers