TSADOK, Shlomi (Shlomi)
2013-Nov-06 10:23 UTC
[libvirt-users] Calling 'virsh' from within a hook script - avoid deadlock?
I'm trying to create a hook that attaches several virtio-scsi disks to a starting vm, and it seems like the hook enters a deadlock while attempting to do so. Is there any workaround around this? Any better way, forking virsh execution somehow? Could anyone explain why this is creating a deadlock in the first place? Isn't libvirt multithreaded? Thanks for the help! Shlomi ### hook script: #!/bin/bash enum_scsi() { scsi_devices=`cd /dev;ls sd[^a]*` } gen_hba_xml() { cat > ./hba.xml << EOF <controller type='scsi' model='virtio-scsi'/> EOF } passthrough_start() { # create virtio-scsi HBA gen_hba_xml virsh attach-device --persistent $domain_name ./hba.xml rm -f ./hba.xml # attache scsi devices to guest enum_scsi for sd in ${scsi_devices[@]} do virsh attach-disk --persistent $domain_name /dev/${sd} ${sd} done } domain_name=$1 domain_event=$2 case $domain_event in start) passthrough_start ;; *) echo "qemu hook called with unexpected options $*" >&2 ;; esac ### starce libvirt: [root@localhost ~]# strace -f -p 14630 Process 14630 attached with 11 threads - interrupt to quit [pid 14640] futex(0xc34ebc, FUTEX_WAIT_PRIVATE, 2303, NULL <unfinished ...> [pid 14638] futex(0xc34ebc, FUTEX_WAIT_PRIVATE, 2303, NULL <unfinished ...> [pid 14637] futex(0xc34ebc, FUTEX_WAIT_PRIVATE, 2303, NULL <unfinished ...> [pid 14636] futex(0xc34ebc, FUTEX_WAIT_PRIVATE, 2303, NULL <unfinished ...> [pid 14635] futex(0x7fcc240ccd80, FUTEX_WAIT_PRIVATE, 2, NULL <unfinished ...> [pid 14639] futex(0xc34ebc, FUTEX_WAIT_PRIVATE, 2303, NULL <unfinished ...> [pid 14634] futex(0x7fcc240ccd80, FUTEX_WAIT_PRIVATE, 2, NULL <unfinished ...> [pid 14631] restart_syscall(<... resuming interrupted call ...> <unfinished ...> [pid 14633] futex(0x7fcc240ccd80, FUTEX_WAIT_PRIVATE, 2, NULL <unfinished ...> [pid 14630] restart_syscall(<... resuming interrupted call ...> <unfinished ...> [pid 14632] futex(0xc34e24, FUTEX_WAIT_PRIVATE, 3091, NULL^C <unfinished ...> ... [pid 14630] poll([{fd=7, events=POLLIN}, {fd=9, events=POLLIN}, {fd=12, events=POLLIN}, {fd=13, events=POLLIN}, {fd=6, events=POLLIN}, {fd=14, events=POLLIN}, {fd=16, events=POLLIN}, {fd=18, events=POLLIN|POLLOUT}, {fd=24, events=POLLIN}], 9, 1927) = 1 ([{fd=18, revents=POLLOUT}]) [pid 14630] gettid() = 14630 [pid 14630] gettid() = 14630 [pid 14630] gettid() = 14630 [pid 14630] gettid() = 14630 [pid 14630] gettid() = 14630 [pid 14630] gettid() = 14630 [pid 14630] gettid() = 14630 [pid 14630] gettid() = 14630 [pid 14630] gettid() = 14630 [pid 14630] gettid() = 14630 [pid 14630] gettid() = 14630 [pid 14630] gettid() = 14630 [pid 14630] write(18, "\0\0\0\34keep\0\0\0\1\0\0\0\1\0\0\0\2\0\0\0\0\0\0\0\0", 28) = 28 ... ### strace bash: [root@localhost ~]# strace -f -p 14783 Process 14783 attached - interrupt to quit wait4(-1, ...
Michal Privoznik
2013-Nov-06 15:17 UTC
Re: [libvirt-users] Calling 'virsh' from within a hook script - avoid deadlock?
On 06.11.2013 11:23, TSADOK, Shlomi (Shlomi) wrote:> I'm trying to create a hook that attaches several virtio-scsi disks to a > starting vm, > > and it seems like the hook enters a deadlock while attempting to do so. > > > > Is there any workaround around this? Any better way, forking virsh > execution somehow? > > > > Could anyone explain why this is creating a deadlock in the first place? > Isn't libvirt multithreaded? > > > > Thanks for the help! > > > > Shlomi > > > > ### hook script: > > > > #!/bin/bash > > > > enum_scsi() { > > scsi_devices=`cd /dev;ls sd[^a]*` > > } > > > > gen_hba_xml() { > > cat > ./hba.xml << EOF > > <controller type='scsi' model='virtio-scsi'/> > > EOF > > } > > > > passthrough_start() { > > # create virtio-scsi HBA > > gen_hba_xml > > virsh attach-device --persistent $domain_name ./hba.xml > > rm -f ./hba.xmlhttp://libvirt.org/hooks.html#recursive Do not do this. Michal
TSADOK, Shlomi (Shlomi)
2013-Nov-06 15:59 UTC
Re: [libvirt-users] Calling 'virsh' from within a hook script - avoid deadlock?
Yes.. I saw that, but I have to :) The issue was solved by converting the hook to Python and using 'subprocess.Popen'. deadlock is gone, all looks good. Regards Shlomi -----Original Message----- From: Michal Privoznik [mailto:mprivozn@redhat.com] Sent: Wednesday, November 06, 2013 5:17 PM To: TSADOK, Shlomi (Shlomi) Cc: libvirt-users@redhat.com Subject: Re: [libvirt-users] Calling 'virsh' from within a hook script - avoid deadlock? On 06.11.2013 11:23, TSADOK, Shlomi (Shlomi) wrote:> I'm trying to create a hook that attaches several virtio-scsi disks to > a starting vm, > > and it seems like the hook enters a deadlock while attempting to do so. > > > > Is there any workaround around this? Any better way, forking virsh > execution somehow? > > > > Could anyone explain why this is creating a deadlock in the first place? > Isn't libvirt multithreaded? > > > > Thanks for the help! > > > > Shlomi > > > > ### hook script: > > > > #!/bin/bash > > > > enum_scsi() { > > scsi_devices=`cd /dev;ls sd[^a]*` > > } > > > > gen_hba_xml() { > > cat > ./hba.xml << EOF > > <controller type='scsi' model='virtio-scsi'/> > > EOF > > } > > > > passthrough_start() { > > # create virtio-scsi HBA > > gen_hba_xml > > virsh attach-device --persistent $domain_name ./hba.xml > > rm -f ./hba.xmlhttp://libvirt.org/hooks.html#recursive Do not do this. Michal
Michal Privoznik
2013-Nov-07 09:16 UTC
Re: [libvirt-users] Calling 'virsh' from within a hook script - avoid deadlock?
On 06.11.2013 16:17, Michal Privoznik wrote:> On 06.11.2013 11:23, TSADOK, Shlomi (Shlomi) wrote: >> [...] > > http://libvirt.org/hooks.html#recursive > > Do not do this. > > Michal >Maybe I should explain a bit why this is not supported. It's true that libvirt is multithreaded. However, not in terms of multiple write/modify accesses to a single domain. That is, when a domain is being started up it is a modify access. Meanwhile, at some point during the transaction the startup hook script is called. If the script decides to start another modify transaction an deadlock occurs. Michal
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