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Re: [Qemu-devel] [PATCH] migration: Fix possible bug for migrate cancel


From: Gonglei (Arei)
Subject: Re: [Qemu-devel] [PATCH] migration: Fix possible bug for migrate cancel
Date: Fri, 28 Mar 2014 09:18:35 +0000

> > >> Return error for migrate cancel, when migration status is not
> > >> MIG_STATE_SETUP or MIG_STATE_ACTIVE. Thus, libvirt can can
> > >> perceive the operation fails.
> > >>
> > >> Signed-off-by: zengjunliang <address@hidden>
> > >> Signed-off-by: Gonglei <address@hidden>
> > >
> > > I think this is done on purpose, because canceling migration is racy.
> > > Instead, libvirt should do "query-migrate" and check if the migration
> > > was completed or canceled.
> >
> > Can you please give more details at how you are triggering the problem
> > with libvirt?  I think Paolo is probably right - the bug is more likely
> > to be in libvirt not expecting the race and not recovering correctly
> > when the race occurs, than it is to be in changing qemu's state algorithm.
> >
> When the migration progress reaches 100%, and the migration status becomes
> MIG_STATE_COMPLETED in Qemu.
> It will take some time which from MIG_STATE_COMPLETED to the migration
> thread resources are recovered.
> If we cancel the migration at this moment, the migrate_fd_cancel function will
> break directly without reporting
> error code. Then, libvirt considers the cancle operation a success, contrary
> facts.
> 

Ping... 


Best regards,
-Gonglei

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