> -----邮件原件-----
> 发件人: Peter Krempa <pkrempa@xxxxxxxxxx>
> 发送时间: 2019年12月13日 15:56
> 收件人: Lin Ma <LMa@xxxxxxxx>
> 抄送: libvir-list@xxxxxxxxxx; berrange@xxxxxxxxxx
> 主题: Re: [PATCH] qemu: snapshot: Fix libvirtd crash in snapshot-revert
>
> On Fri, Dec 13, 2019 at 15:47:36 +0800, Lin Ma wrote:
> > When reverting a running domain to a snapshot(active state), We need
> > to use the FORCE flag for snapshot-revert if current domain
> > configuration is different from the target domain configuration, and
> > this will start a new qemu instance for the target domain.
> >
> > In this situation, if there is existing connection to the domain, say
> > Spice or VNC through virt-manager, Then the libvirtd would crash
> > during snapshot revert because: Both of snapshot revert worker and new
> > worker job 'remoteDispatchDomainOpenGraphicsFd' are waiting for
> > mon->msg->finished in qemuMonitorSend(), We know if IO process
> > resulted in an error with a message, Libvirtd main thread calls
> qemuMonitorIO() to wakeup the waiter.
> > Then mon->msg will be set to NULL in qemuMonitorSend() once the worker
> > GraphicsFD is woken up, which causes snapshot revert worker
> > dereferences this null pointer.
>
> [....]
>
> > Signed-off-by: Lin Ma <lma@xxxxxxxx>
> > ---
> > src/qemu/qemu_monitor.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/src/qemu/qemu_monitor.c b/src/qemu/qemu_monitor.c index
> > ea3e62dc8e..a8344e698b 100644
> > --- a/src/qemu/qemu_monitor.c
> > +++ b/src/qemu/qemu_monitor.c
> > @@ -994,7 +994,7 @@ qemuMonitorSend(qemuMonitorPtr mon,
> > "mon=%p msg=%s fd=%d",
> > mon, mon->msg->txBuffer, mon->msg->txFD);
> >
> > - while (!mon->msg->finished) {
> > + while (mon->msg && !mon->msg->finished) {
>
> This fixes only the symptom. The actual problem is in handling of our job state
> when restarting the qemu process:
>
> Please see the following patches which aim to fix the same problem:
>
> https://www.redhat.com/archives/libvir-list/2019-December/msg00663.html
Indeed, It fixed the root cause, Thanks for your information.
Lin
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