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Date: Tue, 18 Jun 2013 14:57:53 +0200
From: Stefan Hajnoczi <stefanha@gmail.com>
Message-ID: <20130618125753.GL7649@stefanha-thinkpad.redhat.com>
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Subject: Re: [Qemu-devel] [PATCH v2 5/6] net: defer nested call to BH
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To: Liu Ping Fan <qemulist@gmail.com>
Cc: qemu-devel@nongnu.org, Stefan Hajnoczi <stefanha@redhat.com>, mdroth <mdroth@linux.vnet.ibm.com>

On Thu, Jun 13, 2013 at 05:03:05PM +0800, Liu Ping Fan wrote:
> From: Liu Ping Fan <pingfanl@linux.vnet.ibm.com>
> 
> Nested call caused by ->receive() will raise issue like deadlock,
> so postphone it to BH.
> 
> Signed-off-by: Liu Ping Fan <pingfank@linux.vnet.ibm.com>
> ---
>  net/queue.c | 40 ++++++++++++++++++++++++++++++++++++++--
>  1 file changed, 38 insertions(+), 2 deletions(-)

Does this patch belong before the netqueue lock patch?  The commit
history should be bisectable without temporary failures/deadlocks.

> diff --git a/net/queue.c b/net/queue.c
> index 58222b0..9c343ab 100644
> --- a/net/queue.c
> +++ b/net/queue.c
> @@ -24,6 +24,8 @@
>  #include "net/queue.h"
>  #include "qemu/queue.h"
>  #include "net/net.h"
> +#include "block/aio.h"
> +#include "qemu/main-loop.h"
>  
>  /* The delivery handler may only return zero if it will call
>   * qemu_net_queue_flush() when it determines that it is once again able
> @@ -183,6 +185,22 @@ static ssize_t qemu_net_queue_deliver_iov(NetQueue *queue,
>      return ret;
>  }
>  
> +typedef struct NetQueBH {

This file uses "Queue" consistently, please don't add "Que" here.

> @@ -192,8 +210,17 @@ ssize_t qemu_net_queue_send(NetQueue *queue,
>  {
>      ssize_t ret;
>  
> -    if (queue->delivering || !qemu_can_send_packet_nolock(sender)) {
> +    if (queue->delivering || !qemu_can_send_packet_nolock(sender)
> +        || sender->send_queue->delivering) {

Not sure this is safe, we're only holding one NetClientState->peer_lock
and one NetQueue->lock.  How can we access both queue->delivering and
sender->send_queue->delivering safely?