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Date: Thu, 18 Apr 2013 16:11:44 +0200
From: Stefan Hajnoczi <stefanha@gmail.com>
Message-ID: <20130418141144.GA23230@stefanha-thinkpad.redhat.com>
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Subject: Re: [Qemu-devel] [RFC PATCH v4 04/15] net: resolve race of tap
 backend and its peer
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To: Liu Ping Fan <qemulist@gmail.com>
Cc: Stefan Hajnoczi <stefanha@redhat.com>, Jan Kiszka <jan.kiszka@siemens.com>, qemu-devel@nongnu.org, mdroth <mdroth@linux.vnet.ibm.com>, Anthony Liguori <anthony@codemonkey.ws>, Paolo Bonzini <pbonzini@redhat.com>

On Wed, Apr 17, 2013 at 04:39:13PM +0800, Liu Ping Fan wrote:
> From: Liu Ping Fan <pingfank@linux.vnet.ibm.com>
> 
> When vhost net enabled, we should be sure that the user space
> fd handler is not in flight
> 
> Signed-off-by: Liu Ping Fan <pingfank@linux.vnet.ibm.com>
> ---
>  net/tap.c |    5 +++++
>  1 files changed, 5 insertions(+), 0 deletions(-)
> 
> diff --git a/net/tap.c b/net/tap.c
> index 35cbb6e..b5629e3 100644
> --- a/net/tap.c
> +++ b/net/tap.c
> @@ -41,6 +41,7 @@
>  #include "qemu/error-report.h"
>  
>  #include "net/tap.h"
> +#include "util/event_gsource.h"
>  
>  #include "hw/vhost_net.h"
>  
> @@ -327,6 +328,10 @@ static void tap_poll(NetClientState *nc, bool enable)
>      tap_read_poll(s, enable);
>      tap_write_poll(s, enable);
>  
> +    if (!enable) {
> +        /* need sync so vhost can take over polling */
> +        g_source_remove_poll(&s->nsrc->source, &s->nsrc->gfd);
> +    }

We must also re-enable it when .poll(nc, true) is called.

Please drop the comments the previous patch added.  In fact, this patch
can be squashed.

I think there was another vhost sync comment which you haven't addressed
here.  See the previous patch.

Stefan