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

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Message-ID: <CANJ5vPKmP6rFsBgMGFM8DcuGww7B9PxJMSBkUMHNZOa7LJOA2g@mail.gmail.com>
Date:	Tue, 19 Nov 2013 13:38:16 -0800
From:	Michael Dalton <mwdalton@...gle.com>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	Jason Wang <jasowang@...hat.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	lf-virt <virtualization@...ts.linux-foundation.org>,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	Eric Dumazet <edumazet@...gle.com>
Subject: Re: [PATCH net] virtio-net: fix page refcnt leaking when fail to
 allocate frag skb

Great catch Jason. I agree this now raises the larger issue of how to
handle a memory alloc failure in the middle of receive. As Eric mentioned,
we can drop the packet and free the remaining (num_buf) frags.

Michael, perhaps I'm missing something, but why would you prefer
pre-allocating buffers in this case? If the guest kernel is OOM'ing,
dropping packets should provide backpressure.

Also, we could just as easily fail the initial skb alloc in page_to_skb,
and I think that case also needs to be handled now in the same fashion as
a memory allocation failure in receive_mergeable.

Best,

Mike
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