Re: [Qemu-devel] [Bug 1815993] [NEW] drive-backup with iscsi will cause vm disk no response

[Stefan Hajnoczi]

On Fri, Feb 15, 2019 at 03:03:34AM -0000, Cheng Chen wrote:
> When the drive-backup is running, I manually crash the iscsi server（or
> interrupt network, eg. iptables -j DROP）.
> 
> Then after less than 1 minute：
> virsh qemu-monitor-command ${DOMAIN} --pretty '{ "execute": "query-block" }' 
> will block and no any response, until timeout. This is still excusable.
> But, the disk（drive-virtio-disk0）will occur the same situation：in vm os, the 
> disk will block and no any response.
> 
> In other words, when qemu and iscsi-server lose contact, It will cause
> the vm unable.

I haven't tried to reproduce this but I guess QEMU reaches a
synchronization point where it waits for all outstanding requests to
complete.  Since the iSCSI target is unresponsive QEMU gets stuck.

These issues can sometimes be fixed by avoiding the synchronization
point (a backtrace should reveal where the main loop thread is stuck)
but other times it really is necessary to wait for all requests and the
solution isn't as obvious.

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https://bugs.launchpad.net/bugs/1815993

Title:
  drive-backup with iscsi will cause vm disk no response

Status in QEMU:
  New

Bug description:
  virsh qemu-monitor-command ${DOMAIN} '{ "execute" : "drive-backup" ,
  "arguments" : { "device" : "drive-virtio-disk0" , "sync" : "top" ,
  "target" : "iscsi://192.168.1.100:3260/iqn.2019-01.com.iaas/0" } }'

  When the drive-backup is running, I manually crash the iscsi server（or
  interrupt network, eg. iptables -j DROP）.

  Then after less than 1 minute：
  virsh qemu-monitor-command ${DOMAIN} --pretty '{ "execute": "query-block" }' 
will block and no any response, until timeout. This is still excusable.
  But, the disk（drive-virtio-disk0）will occur the same situation：in vm os, the 
disk will block and no any response.

  In other words, when qemu and iscsi-server lose contact, It will cause
  the vm unable.

  ---
  Host: centos 7.5
  qemu version: ovirt-4.2（qemu-2.12.0）
  qemu command line: qemu-system-x86_64 -name guest=test,debug-threads=on -S 
-object 
secret,id=masterKey0,format=raw,file=/var/lib/libvirt/qemu/domain-190-test./master-key.aes
 -machine pc-i440fx-3.1,accel=kvm,usb=off,dump-guest-core=off,mem-merge=off -m 
1024 -mem-prealloc -mem-path /dev/hugepages1G/libvirt/qemu/190-test -realtime 
mlock=off -smp 1,sockets=1,cores=1,threads=1 -uuid 
1c8611c2-a18a-4b1c-b40b-9d82040eafa4 -smbios type=1,manufacturer=IaaS 
-no-user-config -nodefaults -chardev socket,id=charmonitor,fd=31,server,nowait 
-mon chardev=charmonitor,id=monitor,mode=control -rtc base=utc -no-shutdown 
-boot menu=on,strict=on -device piix3-usb-uhci,id=usb,bus=pci.0,addr=0x1.0x2 
-device virtio-serial-pci,id=virtio-serial0,bus=pci.0,addr=0x3 -drive 
file=/opt/vol/sas/fb0c7c37-13e7-41fe-b3f8-f0fbaaeec7ce,format=qcow2,if=none,id=drive-virtio-disk0,cache=writeback
 -device 
virtio-blk-pci,scsi=off,bus=pci.0,addr=0x5,drive=drive-virtio-disk0,id=virtio-disk0,bootindex=1,write-cache=on
 -drive 
file=/opt/vol/sas/bde66671-536d-49cd-8b46-a4f1ea7be513,format=qcow2,if=none,id=drive-virtio-disk1,cache=writeback
 -device 
virtio-blk-pci,scsi=off,bus=pci.0,addr=0x7,drive=drive-virtio-disk1,id=virtio-disk1,write-cache=on
 -netdev tap,fd=33,id=hostnet0,vhost=on,vhostfd=34 -device 
virtio-net-pci,netdev=hostnet0,id=net0,mac=00:85:45:3e:d4:3a,bus=pci.0,addr=0x6 
-chardev pty,id=charserial0 -device isa-serial,chardev=charserial0,id=serial0 
-chardev socket,id=charchannel0,fd=35,server,nowait -device 
virtserialport,bus=virtio-serial0.0,nr=1,chardev=charchannel0,id=channel0,name=org.qemu.guest_agent.0
 -device usb-tablet,id=input0,bus=usb.0,port=1 -vnc 0.0.0.0:0,password -device 
cirrus-vga,id=video0,bus=pci.0,addr=0x2 -device 
virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x4 -msg timestamp=on

  iscsi：
  yum -y install targetcli python-rtslib
  systemctl start target
  systemctl enable target

  targetcli /iscsi create iqn.2019-01.com.iaas

  targetcli /iscsi/iqn.2019-01.com.iaas/tpg1 set attribute
  authentication=0 demo_mode_write_protect=0 generate_node_acls=1

  targetcli /iscsi/iqn.2019-01.com.iaas/tpg1/portals create 192.168.1.100 3260
  targetcli /backstores/fileio create testfile1 /backup/file1 2G
  targetcli /iscsi/iqn.2019-01.com.iaas/tpg1/luns create 
/backstores/fileio/testfile1

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