Re: [Qemu-devel] [PATCH 2/7] migration: only flush when there are no errors

[Daniel P. Berrange]

On Tue, Sep 20, 2011 at 03:24:41PM +0200, Juan Quintela wrote:
> If we have one error while migrating, and then we issuse a
> "migrate_cancel" command, guest hang.  Fix it for flushing only when
> migration is in MIG_STATE_ACTIVE.  In case of error of cancellation,
> don't flush.
> 
> We had an infinite loop at buffered_close()
> 
>         while (!s->has_error && s->buffer_size) {
>             buffered_flush(s);
>             if (s->freeze_output)
>                 s->wait_for_unfreeze(s);
>         }
> 
> There was no errors, there were things to send, and connection was
> broken.  send() returns -EAGAIN, so we freezed output, but we
> unfreeze_output and try again.

I posted a couple of alternative approaches to fixing this
hang problem

http://lists.nongnu.org/archive/html/qemu-devel/2011-08/msg03248.html

My second approach of checking the migration state in migrate_fd_put_buffer()
seems like it would be worthwhile, even with your patch as an additional
safety net against bad code.

Daniel
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