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Date: Tue, 19 Dec 2017 12:48:42 +0800
From: Peter Xu <peterx@redhat.com>
Message-ID: <20171219044842.GY22308@xz-mi>
References: <20171215115123.12959-1-dgilbert@redhat.com>
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In-Reply-To: <20171215115123.12959-1-dgilbert@redhat.com>
Subject: Re: [Qemu-devel] [PATCH] migration: Guard ram_bytes_remaining
 against early call
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To: "Dr. David Alan Gilbert (git)" <dgilbert@redhat.com>
Cc: qemu-devel@nongnu.org, quintela@redhat.com

On Fri, Dec 15, 2017 at 11:51:23AM +0000, Dr. David Alan Gilbert (git) wrote:
> From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
> 
> Calling ram_bytes_remaining during the early part of setup is unsafe
> because the ram_state isn't yet initialised.
> 
> This can happen in the sequence:
>    migrate
>    migrate_cancel
>    info migrate
> 
> if the migrate sticks trying to connect (e.g. to an unresponsive
> destination due to the connect timeout).  Here 'info migrate' sees
> a state of CANCELLING and so assumes the migrate has partially happened.
> 
> partial fix for:
> RH bz: https://bugzilla.redhat.com/show_bug.cgi?id=1525899
> Reported-by: Xianxian Wang <xianwang@redhat.com>
> Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

Reviewed-by: Peter Xu <peterx@redhat.com>

Now we fetch this as long as !COMPLETE:

    if (s->state != MIGRATION_STATUS_COMPLETED) {
        info->ram->remaining = ram_bytes_remaining();
        info->ram->dirty_pages_rate = ram_counters.dirty_pages_rate;
    }

Maybe we should also narrow this down some day.  Thanks,

-- 
Peter Xu