On Tue, 06/02 16:36, Christian Borntraeger wrote: > Paolo, > > I bisected > commit a0710f7995f914e3044e5899bd8ff6c43c62f916 > Author: Paolo Bonzini <pbonz...@redhat.com> > AuthorDate: Fri Feb 20 17:26:52 2015 +0100 > Commit: Kevin Wolf <kw...@redhat.com> > CommitDate: Tue Apr 28 15:36:08 2015 +0200 > > iothread: release iothread around aio_poll > > to cause a problem with hanging guests. > > Having many guests all with a kernel/ramdisk (via -kernel) and > several null block devices will result in hangs. All hanging > guests are in partition detection code waiting for an I/O to return > so very early maybe even the first I/O. > > Reverting that commit "fixes" the hangs. > Any ideas?
Christian, I can't reproduce this on my x86 box with virtio-blk-pci. Do you have a reproducer for x86? Or could you collect backtraces for all the threads in QEMU when it hangs? My long shot is that the main loop is blocked at aio_context_acquire(ctx), while the iothread of that ctx is blocked at aio_poll(ctx, blocking). Thanks, Fam > > Christian > > PS: A guest xml looks like > > > <domain type='kvm' xmlns:qemu='http://libvirt.org/schemas/domain/qemu/1.0'> > <name>test2</name> > <uuid>13bd8253-9abb-4be8-9399-73b899762aaa</uuid> > <memory unit='KiB'>286720</memory> > <currentMemory unit='KiB'>286720</currentMemory> > <vcpu placement='static'>10</vcpu> > <iothreads>8</iothreads> > <cputune> > <shares>12</shares> > </cputune> > <os> > <type arch='s390x' machine='s390-ccw-virtio'>hvm</type> > <kernel>/boot/vmlinux-4.0.0+</kernel> > <initrd>/boot/ramdisk.reboot</initrd> > <cmdline>root=/dev/ram0</cmdline> > <boot dev='hd'/> > </os> > <clock offset='utc'/> > <on_poweroff>destroy</on_poweroff> > <on_reboot>restart</on_reboot> > <on_crash>preserve</on_crash> > <devices> > <controller type='usb' index='0' model='none'/> > <console type='pty'> > <target type='sclp' port='0'/> > </console> > <memballoon model='none'/> > </devices> > <qemu:commandline> > <qemu:arg value='-drive'/> > <qemu:arg value='driver=null-aio,id=null1,if=none,size=100G'/> > <qemu:arg value='-device'/> > <qemu:arg > value='virtio-blk-ccw,drive=null1,serial=null1,iothread=iothread1'/> > <qemu:arg value='-drive'/> > <qemu:arg value='driver=null-aio,id=null2,if=none,size=100G'/> > <qemu:arg value='-device'/> > <qemu:arg > value='virtio-blk-ccw,drive=null2,serial=null2,iothread=iothread2'/> > <qemu:arg value='-drive'/> > <qemu:arg value='driver=null-aio,id=null3,if=none,size=100G'/> > <qemu:arg value='-device'/> > <qemu:arg > value='virtio-blk-ccw,drive=null3,serial=null3,iothread=iothread3'/> > <qemu:arg value='-drive'/> > <qemu:arg value='driver=null-aio,id=null4,if=none,size=100G'/> > <qemu:arg value='-device'/> > <qemu:arg > value='virtio-blk-ccw,drive=null4,serial=null4,iothread=iothread4'/> > <qemu:arg value='-drive'/> > <qemu:arg value='driver=null-aio,id=null5,if=none,size=100G'/> > <qemu:arg value='-device'/> > <qemu:arg > value='virtio-blk-ccw,drive=null5,serial=null5,iothread=iothread5'/> > <qemu:arg value='-drive'/> > <qemu:arg value='driver=null-aio,id=null6,if=none,size=100G'/> > <qemu:arg value='-device'/> > <qemu:arg > value='virtio-blk-ccw,drive=null6,serial=null6,iothread=iothread6'/> > <qemu:arg value='-drive'/> > <qemu:arg value='driver=null-aio,id=null7,if=none,size=100G'/> > <qemu:arg value='-device'/> > <qemu:arg > value='virtio-blk-ccw,drive=null7,serial=null7,iothread=iothread7'/> > <qemu:arg value='-drive'/> > <qemu:arg value='driver=null-aio,id=null8,if=none,size=100G'/> > <qemu:arg value='-device'/> > <qemu:arg > value='virtio-blk-ccw,drive=null8,serial=null8,iothread=iothread8'/> > </qemu:commandline> > </domain> > >
