From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jarek Poplawski Subject: Re: [PATCH] af_packet: Don't use skb after dev_queue_xmit() Date: Thu, 7 Jan 2010 18:56:10 +0100 Message-ID: <20100107175610.GA3088@del.dom.local> References: <4B454A16.3030909@majjas.com> <4B455C62.6030504@majjas.com> <20100106205343.5460d658@nehalam> <4B4571D5.30002@majjas.com> <4B457711.1040008@majjas.com> <4B458B36.6050509@majjas.com> <20100107074756.GB6258@ff.dom.local> <4B459368.2000503@majjas.com> <20100107082140.GB7229@ff.dom.local> <4B45F7D7.3060308@majjas.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Stephen Hemminger , David Miller , akpm@linux-foundation.org, flyboy@gmail.com, linux-kernel@vger.kernel.org, netdev@vger.kernel.org To: Michael Breuer Return-path: Content-Disposition: inline In-Reply-To: <4B45F7D7.3060308@majjas.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On Thu, Jan 07, 2010 at 10:03:51AM -0500, Michael Breuer wrote: > On 1/7/2010 3:21 AM, Jarek Poplawski wrote: > >On Thu, Jan 07, 2010 at 02:55:20AM -0500, Michael Breuer wrote: > >>Unless I misread the code, I think that in some cases e skb is actually > >>freed if the cfq (among others perhaps) scheduler returns an error on > >>enqueue (flow control perhaps). Thus with alternative 1, it is possible > >>that the skb is acted upon after being freed - this would be consistent > >>with the DMAR errors I saw. > >I can't see your point: could you give some scenario? > > > >Jarek P. > With NET_CLS_ACT set, net_dev_enqueue can return an error after > freeing the skb. Alternative 1 disregards the error and assumes the > skb is still valid. The original code and alternative 2 exit the > loop assuming the skb has been freed. Not exactly: alternative 1 disregards the error, and tries to send next skbs if the message was longer. After consuming all the message it returns without err code (at least wrt. dev_queue_xmit). This is quite often practice to skip dev_queue_xmit() return (try to grep in net\). It should never touch any part of an earlier sent skb. Jarek P.