linux-kernel - Re: [PATCH v2 3/4] btrfs: Add zstd support

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Message-ID: <20170708030706.tle2mpfe376jneft@angband.pl>
Date:   Sat, 8 Jul 2017 05:07:06 +0200
From:   Adam Borowski <kilobyte@...band.pl>
To:     Nick Terrell <terrelln@...com>
Cc:     Kernel Team <Kernel-team@...com>, Chris Mason <clm@...com>,
        Yann Collet <cyan@...com>, David Sterba <dsterba@...e.cz>,
        "linux-btrfs@...r.kernel.org" <linux-btrfs@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 3/4] btrfs: Add zstd support

On Sat, Jul 08, 2017 at 01:40:18AM +0200, Adam Borowski wrote:
> On Fri, Jul 07, 2017 at 11:17:49PM +0000, Nick Terrell wrote:
> > On 7/6/17, 9:32 AM, "Adam Borowski" <kilobyte@...band.pl> wrote:
> > > Got a reproducible crash on amd64:
>
> > Thanks for the bug report Adam! I'm looking into the failure, and haven't
> > been able to reproduce it yet. I've built my kernel from your tree, and
> > I ran your script with the kernel.tar tarball 100 times, but haven't gotten
> > a failure yet.
> 
> > I have a few questions to guide my debugging.
> > 
> > - How many cores are you running with? I’ve run the script with 1, 2, and 4 cores.
> > - Which version of gcc are you using to compile the kernel? I’m using gcc-6.2.0-5ubuntu12.
> > - Are the failures always in exactly the same place, and does it fail 100%
> >   of the time or just regularly?
> 
> 6 cores -- all on bare metal.  gcc-7.1.0-9.
> Lemme try with gcc-6, a different config or in a VM.

I've tried the following:
* gcc-6, defconfig (+btrfs obviously)
* gcc-7, defconfig
* gcc-6, my regular config
* gcc-7, my regular config
* gcc-7, debug + UBSAN + etc
* gcc-7, defconfig, qemu-kvm with only 1 core

Every build with gcc-7 reproduces the crash, every with gcc-6 does not.

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