Re: [Qemu-devel] QEMU abort when network serivce is restarted during live migration with vhost-user as the network backend

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Yori Fang (fangying1@huawei.com) wrote:
> 
> 
> 在 2017/11/14 19:40, Marc-André Lureau 写道:
> > Hi
> > 
> > On Tue, Nov 14, 2017 at 8:09 AM, fangying <fangying1@huawei.com> wrote:
> >> Hi all,
> >>
> >> We have a vm running migration with vhost-user as network backend, we notice that qemu will abort when openvswitch is restarted
> >> when MEMORY_LISTENER_CALL_GLOBAL(log_global_start, Forward) is called. The reasion is clear that vhost_dev_set_log returns -1 because
> >> the network connection is temporarily lost due to the restart of openvswitch service.
> >>
> >> Below is the trace of the call stack.
> >>
> >> #0  0x00007f868ed971d7 in raise() from /usr/lib64/libc.so.6
> >> #1  0x00007f868ed988c8 in abort() from /usr/lib64/libc.so.6
> >> #2  0x00000000004d0d35 in vhost_log_global_start (listener=<optimized out>) at /usr/src/debug/qemu-kvm-2.8.1/hw/virtio/vhost.c:794
> >> #2  0x0000000000486bd2 in memory_global_dirty_log_start at /usr/src/debug/qemu-kvm-2.8.1/memory.c:2304
> >> #3  0x0000000000486dcd in ram_save_init_globals at /usr/src/debug/qemu-kvm-2.8.1/migration/ram.c:2072
> >> #4  0x000000000048c185 in ram_save_setup (f=0x25e6ac0, opaque=<optimized out>) at /usr/src/debug/qemu-kvm-2.8.1/migration/ram.c:2093
> >> #5  0x00000000004fbee2 in qemu_savevm_state_begin at /usr/src/debug/qemu-kvm-2.8.1/migration/savevm.c:956
> >> #6  0x000000000083d8f8 in migration_thread at migration/migration.c:2198
> >>
> >> static void vhost_log_global_start(MemoryListener *listener)
> >> {
> >>     int r;
> >>
> >>     r = vhost_migration_log(listener, true);
> >>     if (r < 0) {
> >>         abort();   /* branch taken */
> >>     }
> >> }
> >>
> >> What confuse me is that
> >> 1. do we really need to abort here ?
> > 
> > Not if we have a sane way to handle the situation. It make sense
> > though to not want to support that use case (restarting the vhost-user
> > process during migration).
> > 
> >> 2. all member of callbacks in MemoryListener returned with type void, we cannot judge in any upper function on the call stack.
> >> Can we just cancel migration here instead of calling abort ? like:
> > 
> > That would be acceptable to me, but there should be a better way than
> > calling qmp_migrate_cancel() (we need to give a reason for cancelling,
> > and report it to user). Juan should be able to help.
> 
> I agree with you, we'd better give more details here instead of passing NULL in qmp_migrate_cancel.

This is an unfortunate place to want to kill the migration; cancel is
the wrong call to use though (it's for users to cancel it).
I think the only way to do it is to call
migrate_fd_error(migrate_get_current(),...)

It's not nice though, but the only one I can think of from here.

Dave

> > 
> >>
> >> diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
> >> index ddc42f0..27ae4a2 100644
> >> --- a/hw/virtio/vhost.c
> >> +++ b/hw/virtio/vhost.c
> >> @@ -27,6 +27,7 @@
> >>  #include "hw/virtio/virtio-access.h"
> >>  #include "migration/blocker.h"
> >>  #include "sysemu/dma.h"
> >> +#include "qmp-commands.h"
> >>
> >>  /* enabled until disconnected backend stabilizes */
> >>  #define _VHOST_DEBUG 1
> >> @@ -885,7 +886,7 @@ static void vhost_log_global_start(MemoryListener *listener)
> >>
> >>      r = vhost_migration_log(listener, true);
> >>      if (r < 0) {
> >> -        abort();
> >> +        qmp_migrate_cancel(NULL);
> >>      }
> >>  }
> >>
> >> @@ -895,7 +896,7 @@ static void vhost_log_global_stop(MemoryListener *listener)
> >>
> >>      r = vhost_migration_log(listener, false);
> >>      if (r < 0) {
> >> -        abort();
> >> +        qmp_migrate_cancel(NULL);
> >>      }
> >>  }
> >>
> >>
> >>
> >>
> > 
> > 
> > 
> 
> 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK