[Qemu-devel] [Bug 595438] Re: KVM segmentation fault, using SCSI+writeback and linux 2.4 guest

[Imre Gergely]

I can confirm the segfault with the same Fedora 1 install. It doesn't
even get to 50%, it segfaults way earlier. In fact I tried this:

- kvm-img create -f qcow2 /store/KVM/test.qcow2 2G
- address@hidden:~$ sudo LC_ALL=C 
PATH=/usr/local/sbin:/usr/local/bin:/usr/bin:/usr/sn:/sbin:/bin 
QEMU_AUDIO_DRV=none /usr/bin/kvm -M pc-0.12 -enable-kvm -m 256 -smp 1 -name 
spamsender -uuid b9cacd5e-08f7-41fd-78c8-89cec59af881 -chardev 
socket,id=monitor,path=/var/lib/libvirt/qemu/test.monitor,server,nowait 
-monitor chardev:monitor -boot d -drive 
file=/store/Kits/isos/yarrow-i386-disc1.iso,if=ide,media=cdrom,index=2 -drive 
file=/store/KVM/test.qcow2,if=scsi,index=0,format=qcow2,cache=writeback -net 
nic,macaddr=00:00:00:00:00:00,vlan=0,name=nic.0 -net tap,vlan=0,name=tap.0 
-chardev pty,id=serial0 -serial chardev:serial0 -parallel none -usb -vnc 
172.16.21.1:1 -vga cirrus
(mostly the same options, renamed only to "test whatever")
- Fedora text install, everything on default, "Personal Desktop", 
auto-partitioning
- after it complained that the stuff wouldn't fit (because the partitions are 
too small), I gave it another go (without reboot) and it crapped out instantly.

----------
address@hidden:~$ sudo LC_ALL=C 
PATH=/usr/local/sbin:/usr/local/bin:/usr/bin:/usr/sn:/sbin:/bin 
QEMU_AUDIO_DRV=none /usr/bin/kvm -M pc-0.12 -enable-kvm -m 256 -smp 1 -name 
spamsender -uuid b9cacd5e-08f7-41fd-78c8-89cec59af881 -chardev 
socket,id=monitor,path=/var/lib/libvirt/qemu/test.monitor,server,nowait 
-monitor chardev:monitor -boot d -drive 
file=/store/Kits/isos/yarrow-i386-disc1.iso,if=ide,media=cdrom,index=2 -drive 
file=/store/KVM/test.qcow2,if=scsi,index=0,format=qcow2,cache=writeback -net 
nic,macaddr=00:00:00:00:00:00,vlan=0,name=nic.0 -net tap,vlan=0,name=tap.0 
-chardev pty,id=serial0 -serial chardev:serial0 -parallel none -usb -vnc 
172.16.21.1:1 -vga cirrus
char device redirected to /dev/pts/12
pci_add_option_rom: failed to find romfile "pxe-rtl8139.bin"
scsi-disk: Tag 0x0 already in use
Segmentation fault
----------

I'll try the -proposed package in a little while.

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https://bugs.launchpad.net/bugs/595438

Title:
  KVM segmentation fault, using SCSI+writeback and linux 2.4 guest

Status in Kernel Virtual Machine:
  Confirmed
Status in QEMU:
  Fix Committed
Status in qemu-kvm:
  Fix Released
Status in “qemu-kvm” package in Ubuntu:
  Fix Released
Status in “qemu-kvm” source package in Lucid:
  Fix Committed
Status in “qemu-kvm” package in Debian:
  Fix Released

Bug description:
  I Use Ubuntu 32 bit 10.04 with standard KVM.
I have Intel E7600  @ 3.06GHz processor with VMX

In this system I Run:
LC_ALL=C PATH=/usr/local/sbin:/usr/local/bin:/usr/bin:/usr/sbin:/sbin:/bin 
QEMU_AUDIO_DRV=none /usr/bin/kvm -M pc-0.12 -enable-kvm -m 256 -smp 1 -name 
spamsender -uuid b9cacd5e-08f7-41fd-78c8-89cec59af881 -chardev 
socket,id=monitor,path=/var/lib/libvirt/qemu/spamsender.monitor,server,nowait 
-monitor chardev:monitor -boot d -drive 
file=/mnt/megadiff/cdiso_400_130.iso,if=ide,media=cdrom,index=2 -drive 
file=/home/mmarkk/spamsender2.img,if=scsi,index=0,format=qcow2,cache=writeback 
-net nic,macaddr=00:00:00:00:00:00,vlan=0,name=nic.0 -net tap,vlan=0,name=tap.0 
-chardev pty,id=serial0 -serial chardev:serial0 -parallel none -usb -vnc 
127.0.0.1:0 -vga cirrus

.iso image contain custom distro of 2.4-linux kernel based system. During 
install process (when .tar.gz actively unpacked), kvm dead with segmentation 
fault.

And ONLY when I choose scsi virtual disk and writeback simultaneously.
But, writeback+ide, writethrough+scsi works OK.

I use qcow2. It seems, that qcow does not have such problems.

Virtual machine get down at random time during file copy. It seems, when qcow2 
file size need to be expanded.

IMPACT: kvm used with scsi virtual disk and writeback dies with segfault.

FIX: is the inclusion of a patch cherry-picked from upstream which dequeues
requests before invoking callbacks.  It is at
http://bazaar.launchpad.net/~serge-hallyn/ubuntu/lucid/qemu-kvm/fix-scsi-writeback/revision/70

TO REPRODUCE: See the command above.

REGRESSION POTENTIAL: this is cherry-picked from upstream, and has been
tested by the bug reporter with no ill effects.