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Subject: Re: [PATCH v2 3/4] btrfs: Add zstd support
To: Adam Borowski <kilobyte@angband.pl>, Nick Terrell <terrelln@fb.com>
Cc: Kernel Team <Kernel-team@fb.com>, Chris Mason <clm@fb.com>,
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From: "Austin S. Hemmelgarn" <ahferroin7@gmail.com>
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Date: Mon, 10 Jul 2017 08:36:44 -0400
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On 2017-07-07 23:07, Adam Borowski wrote:
> 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@angband.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.
> 
Got a GCC7 tool-chain built, and I can confirm this here too, tested 
with various numbers of cores ranging from 1-32 in a QEMU+KVM VM, with 
various combinations of debug options and other config switches.