From mboxrd@z Thu Jan 1 00:00:00 1970 Subject: Re: [RFC][PATCH 2/9] deadlock prevention core From: Peter Zijlstra In-Reply-To: <20060809131942.GY14627@postel.suug.ch> References: <20060808193345.1396.16773.sendpatchset@lappy> <20060808211731.GR14627@postel.suug.ch> <44D93BB3.5070507@google.com> <20060808.183920.41636471.davem@davemloft.net> <44D976E6.5010106@google.com> <20060809131942.GY14627@postel.suug.ch> Content-Type: text/plain Date: Wed, 09 Aug 2006 16:07:20 +0200 Message-Id: <1155132440.12225.70.camel@twins> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Thomas Graf Cc: Daniel Phillips , David Miller , linux-mm@kvack.org, linux-kernel@vger.kernel.org, netdev@vger.kernel.org List-ID: On Wed, 2006-08-09 at 15:19 +0200, Thomas Graf wrote: > * Daniel Phillips 2006-08-08 22:47 > > David Miller wrote: > > >From: Daniel Phillips > > >>Can you please characterize the conditions under which skb->dev changes > > >>after the alloc? Are there writings on this subtlety? > > > > > >The packet scheduler and classifier can redirect packets to different > > >devices, and can the netfilter layer. > > > > > >The setting of skb->dev is wholly transient and you cannot rely upon > > >it to be the same as when you set it on allocation. > > > > > >Even simple things like the bonding device change skb->dev on every > > >receive. > > > > Thankyou, this is easily fixed. > > It's not that simple, in order to just fix the most obvious case > being packet forwarding when skb->dev changes its meaning from > device the packet is coming from to device the packet will be leaving > on is difficult. > > You can't unreserve at that point so you need to keep the original > skb->dev. Since the packet is mostly likely queued before freeing > you will lose the refcnt on the original skb->dev. Keeping a > refcnt just for this memalloc stuff is out of question. Even keeping > the ifindex on a best effort basis is unlikely an option, sk_buff is > way overweight already. I think Daniel was thinking of adding struct net_device * sk_buff::alloc_dev, I know I was after reading the first few mails. However if adding a field there is strict no-no.... /me takes a look at struct sk_buff Hmm, what does sk_buff::input_dev do? That seems to store the initial device? -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org