netdev - Re: [PATCH net] virtio-net: fix page refcnt leaking when fail to allocate frag skb

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Message-ID: <1384869828.8604.97.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Tue, 19 Nov 2013 06:03:48 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Jason Wang <jasowang@...hat.com>
Cc:	rusty@...tcorp.com.au, mst@...hat.com,
	virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, Michael Dalton <mwdalton@...gle.com>,
	Eric Dumazet <edumazet@...gle.com>
Subject: Re: [PATCH net] virtio-net: fix page refcnt leaking when fail to
 allocate frag skb

On Tue, 2013-11-19 at 16:05 +0800, Jason Wang wrote:
> We need to drop the refcnt of page when we fail to allocate an skb for frag
> list, otherwise it will be leaked. The bug was introduced by commit
> 2613af0ed18a11d5c566a81f9a6510b73180660a ("virtio_net: migrate mergeable rx
> buffers to page frag allocators").
> 
> Cc: Michael Dalton <mwdalton@...gle.com>
> Cc: Eric Dumazet <edumazet@...gle.com>
> Cc: Rusty Russell <rusty@...tcorp.com.au>
> Cc: Michael S. Tsirkin <mst@...hat.com>
> Signed-off-by: Jason Wang <jasowang@...hat.com>
> ---
> The patch was needed for 3.12 stable.

Good catch, but if we return from receive_mergeable() in the 'middle'
of the frags we would need for the current skb, who will
call the virtqueue_get_buf() to flush the remaining frags ?

Don't we also need to call virtqueue_get_buf() like 

while (--num_buf) {
    buf = virtqueue_get_buf(rq->vq, &len);
    if (!buf)
        break;
    put_page(virt_to_head_page(buf));
}

?




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