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[67.180.167.114]) by smtp.gmail.com with ESMTPSA id k125-v6sm3855581pgk.41.2018.08.02.08.07.12 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 02 Aug 2018 08:07:13 -0700 (PDT) Subject: Re: AW: AW: PROBLEM: Kernel Oops in UDP stack To: Marcel Hellwig , 'Eric Dumazet' , David Laight , "'davem@davemloft.net'" , "'kuznet@ms2.inr.ac.ru'" , "'yoshfuji@linux-ipv6.org'" , "'andrew@lunn.ch'" Cc: "'netdev@vger.kernel.org'" , "'linux-kernel@vger.kernel.org'" , Matthias Wystrik References: <18092446dfa7435aaa8deaab65afbf23@ZCOM03.mut-group.com> <96753ca4-88fe-aa26-b439-6e22eaf8b524@gmail.com> <9f9d731107594b368504cbbaf698bc3d@ZCOM03.mut-group.com> <405319c1-2fa0-e1b5-7173-b19d9769d98a@gmail.com> <18341daf5b2c458db8e30299d6cddafc@ZCOM03.mut-group.com> From: Eric Dumazet Message-ID: Date: Thu, 2 Aug 2018 08:07:11 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.6.0 MIME-Version: 1.0 In-Reply-To: <18341daf5b2c458db8e30299d6cddafc@ZCOM03.mut-group.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 08/02/2018 06:57 AM, Marcel Hellwig wrote: >>> There are actually 2 faults, difficult to quickly sort out the merged tracebacks. >>> You are also running a rather old kernel: Linux version 3.4.113. >>> >>> It may well be that whichever ethernet driver generated the misaligned >>> frame has since been fixed. >> >> A misalign frame driver problem would have faulted earlier in IP stack, much before we perform the copy to user space in udp_recvmsg() >> > > JFYI: we are talking about the lpc_eth driver[0] #57c10b6 , which is not the newest, but all newer did not fix a major problem (at least the commit messages are not screaming: WARNING, UNALIGNED MEMORY!). Is there a diagram/document how a ip packet travels down the code? From the MAC/phy driver to udp_recvmsg? It's not that obvious for me, but maybe it is something I can work with. > > > [0]: https://elixir.bootlin.com/linux/v3.4.113/source/drivers/net/ethernet/nxp/lpc_eth.c > > Regards, > Marcel > Well, this driver does not use NET_IP_ALIGN reservation, meaning IP header is not 4-byte aligned. No idea why mis-alignments are okay in IP layer, but not in UDP You could try to patch it to use netdev_alloc_skb_ip_align() instead of dev_alloc_skb()