From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: Re: [PATCH net] virtio-net: fix page refcnt leaking when fail to allocate frag skb Date: Wed, 20 Nov 2013 11:00:09 +0200 Message-ID: <20131120090009.GC19341@redhat.com> References: <1384848307-7217-1-git-send-email-jasowang@redhat.com> <1384869828.8604.97.camel@edumazet-glaptop2.roam.corp.google.com> <20131119204909.GA15004@redhat.com> <1384896996.8604.120.camel@edumazet-glaptop2.roam.corp.google.com> <20131119215312.GE15004@redhat.com> <1384898411.8604.127.camel@edumazet-glaptop2.roam.corp.google.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: Eric Dumazet , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, lf-virt , Eric Dumazet To: Michael Dalton Return-path: Content-Disposition: inline In-Reply-To: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org List-Id: netdev.vger.kernel.org On Tue, Nov 19, 2013 at 05:34:16PM -0800, Michael Dalton wrote: > Hi, > > After further reflection I think we're looking at two related issues: > (a) a memory leak that Jason has identified that occurs when a memory > allocation fails in receive_mergeable. Jasons commit solves this issue. > (b) virtio-net does not dequeue all buffers for a packet in the > case that an error occurs on receive and mergeable receive buffers is > enabled. > > For (a), this bug is new and due to changes in 2613af0ed18a, and the > net impact is memory leak on the physical page. However, I believe (b) > has always been possible in some form because if page_to_skb() returns > NULL (e.g., due to SKB allocation failure), receive_mergeable is never > called. AFAICT this is also the behavior prior to 2613af0ed18a. > > The net impact of (b) would be that virtio-net would interpret a packet > buffer that is in the middle of a mergeable packet as the start of a > new packet, which is definitely also a bug (and the buffer contents > could contain bytes that resembled a valid virtio-net header). > > A solution for (b) will require handling both the page_to_skb memory > allocation failures and the memory allocation failures in > receive_mergeable introduced by 2613af0ed18a. > > Best, > > Mike Absolutely. I missed this fact yesterday night but I can see it clearly in the morning.