On 7/10/17, 5:36 AM, "Austin S. Hemmelgarn" <ahferro...@gmail.com> wrote: > 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" <kilob...@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.
I was running in an Ubuntu 16.10 VM on a MacBook Pro. I built with gcc-6.2 with KASAN, and couldn't trigger it, as expected. I built with gcc-7.1.0 built from source, and couldn't reproduce it. However, when I set up qemu-kvm on another device, and compiled with gcc-7.1.0 built from source, I was able to reproduce the bug. Now that I can reproduce it, I'll look into a fix. Thanks Adam and Austin for finding, reproducing, and verifying the bug.