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Bug 699754

Summary: sys-kernel/gentoo-sources-4.19.82: libvirt-guests are stuck in reboot-loop
Product: Gentoo Linux Reporter: tastytea <gentoo>
Component: Current packagesAssignee: Gentoo Kernel Bug Wranglers and Kernel Maintainers <kernel>
Severity: normal CC: fabian, jbuchert+genbug, randy
Priority: Normal    
Version: unspecified   
Hardware: AMD64   
OS: Linux   
Package list:
Runtime testing required: ---
Bug Depends on: 700416    
Bug Blocks:    
Attachments: libvirt log of guest
dmesg excerpt

Description tastytea 2019-11-10 16:24:16 UTC
After upgrading from 4.19.72 to 4.19.82, my VMs are stuck in a reboot-loop. The boot up to Grub is fine, but when I select an item in the boot menu, the guest reboots after a short while. I can't see any output. I don't see anything unusual in the logs but I'll attach the log from libvirt and dmesg. After I switch back to .72, the guests boots fine. The same issue manifests when booting from "CD-ROM".

The .82-kernel is compiled with sys-devel/gcc-9.2.0-r2, the old was compiled with 8.3. The only change in the kernel config is CONFIG_GCC_VERSION.

I tried to reproduce the issue and found a possible clue: The affected machines both have an Intel Core 2 DUO CPU (T7300 and P8700). The machine that is not affected has an AMD CPU (A10-9700).

Reproducible: Always
Comment 1 tastytea 2019-11-10 16:25:31 UTC
Created attachment 595666 [details]
libvirt log of guest
Comment 2 tastytea 2019-11-10 16:26:16 UTC
Created attachment 595668 [details]
dmesg excerpt
Comment 3 tastytea 2019-11-10 22:19:44 UTC
I recompiled the kernel with sys-devel/gcc-8.3.0-r1 to be sure it's not that; the issue persists.
Comment 4 xyz 2019-11-11 18:52:32 UTC
Same issue after upgrading from linux-4.14.143-gentoo to linux-4.14.152-gentoo on the VM host. After reboot host works fine, but guests with linux-4.14.143-gentoo are stuck in a bootloop.
All kernels compiled with sys-devel/gcc-8.3.0-r1
Comment 5 Mike Pagano gentoo-dev 2019-11-14 16:19:08 UTC
Are you able to do a git bisect between the last working kernel and the first on working kernel?
Comment 6 tastytea 2019-11-14 18:25:54 UTC
Yes, I'll get right to work. :-)
Comment 7 tastytea 2019-11-15 18:31:32 UTC
496cf984a60edb5534118a596613cc9971e406e8 is the first bad commit (commit 16cfacc8085782dab8e365979356ce1ca87fd6cc upstream).
Comment 8 Thomas Deutschmann gentoo-dev Security 2019-11-17 23:10:12 UTC
Upstream patch: bf03d4f9334728bf7c8ffc7de787df48abd6340e 

Will be in next stable kernels.
Comment 9 tastytea 2019-11-18 03:34:00 UTC
I can confirm the fix works with 4.19.82.