From mboxrd@z Thu Jan 1 00:00:00 1970 From: Arvid Brodin Subject: Re: [RFC] net/hsr: Add support for IEC 62439-3 High-availability Seamless Redundancy Date: Mon, 14 May 2012 18:11:44 +0000 Message-ID: <4FB14ADD.3050708@xdin.com> References: <4F71BEAD.5080605@enea.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7BIT Cc: "David S. Miller" , Stephen Hemminger , Bruno Ferreira , Arvid Brodin , Christian Borntraeger , Herbert Xu To: "netdev@vger.kernel.org" Return-path: Received: from spam1.webland.se ([91.207.112.90]:51496 "EHLO spam1.webland.se" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757033Ab2ENSLq convert rfc822-to-8bit (ORCPT ); Mon, 14 May 2012 14:11:46 -0400 In-Reply-To: <4F71BEAD.5080605@enea.com> Content-Language: en-US Content-ID: <194CD4078011CB40A3AAEA7CA61B73C3@redbull.xdin.com> Sender: netdev-owner@vger.kernel.org List-ID: On 2012-03-27 15:20, Arvid Brodin wrote: > Hi! *snip* > > 2) I have a locking problem that I haven't managed to figure out. This happens > the first time I send any packet (hsr_dev_xmit() in hsr_device.c:121, called > from hsr_device.c:147). It happens even if I set skb2 to NULL (i.e. only send > one copy): > > ============================================= > [ INFO: possible recursive locking detected ] > 2.6.37 #118 > --------------------------------------------- > swapper/0 is trying to acquire lock: > (_xmit_ETHER#2){+.-...}, at: [<901bf38e>] sch_direct_xmit+0x24/0x152 > > but task is already holding lock: > (_xmit_ETHER#2){+.-...}, at: [<901b4d1a>] dev_queue_xmit+0x31e/0x3cc > > other info that might help us debug this: > 4 locks held by swapper/0: > #0: (&n->timer){+.-...}, at: [<9002bc20>] run_timer_softirq+0x98/0x184 > #1: (rcu_read_lock_bh){.+....}, at: [<901b49fc>] dev_queue_xmit+0x0/0x3cc > #2: (_xmit_ETHER#2){+.-...}, at: [<901b4d1a>] dev_queue_xmit+0x31e/0x3cc > #3: (rcu_read_lock_bh){.+....}, at: [<901b49fc>] dev_queue_xmit+0x0/0x3cc > > stack backtrace: > Call trace: > [<9001c640>] dump_stack+0x18/0x20 > [<90040eac>] validate_chain+0x40c/0x9ac > [<90041a58>] __lock_acquire+0x60c/0x670 > [<90042f32>] lock_acquire+0x3a/0x48 > [<902201a4>] _raw_spin_lock+0x20/0x44 > [<901bf38e>] sch_direct_xmit+0x24/0x152 > [<901b4c14>] dev_queue_xmit+0x218/0x3cc > [<9021c2e0>] slave_xmit+0x10/0x14 > [<9021c540>] hsr_dev_xmit+0x88/0x8c > [<901b4942>] dev_hard_start_xmit+0x3c6/0x480 > [<901b4d34>] dev_queue_xmit+0x338/0x3cc > [<901e3cd8>] arp_xmit+0x8/0xc > [<901e4436>] arp_send+0x2a/0x2c > [<901e4e74>] arp_solicit+0x15c/0x170 > [<901bad0c>] neigh_timer_handler+0x1c0/0x204 > [<9002bc8a>] run_timer_softirq+0x102/0x184 > [<900287d8>] __do_softirq+0x64/0xe0 > [<9002896a>] do_softirq+0x26/0x48 > [<90028a66>] irq_exit+0x2e/0x64 > [<90019f16>] do_IRQ+0x46/0x5c > [<90018428>] irq_level0+0x18/0x60 > [<9021cc16>] rest_init+0x72/0x98 > [<9000063c>] start_kernel+0x21c/0x258 > [<00000000>] 0x0 > > Any idea why this happens? I need help! I've spent a few days digging into this and the key apparently is NETIF_F_LLTX. The problem seems to be that HARD_TX_LOCK is called more than once, first for my virtual hsr device and then, recursively, for each of the slaves in turn. (At least that's where lockdep complains - at __netif_tx_lock(), that is.) At first I just could not understand why both the VLAN and the bonding code got away with recursive calls to dev_queue_xmit() but I didn't. After some gooling (a lot, actually) I found some references to the NETIF_F_LLTX flag (here's one: http://lwn.net/Articles/121566/). I realised both VLAN and bonding code set this flag. And sure enough, if I set it for my hsr device lockdep does not complain any more. But NETIF_F_LLTX is described as deprecated in both netdevice.h and in Documentation/networking/netdevices.txt. Is there an alternative solution that I should use instead? (To recap, a hsr device is a virtual device which uses two Ethernet devices as slaves. This gives redundancy with instant failover, and since nodes are connected in a ring topology, uses less cabling than duplication.) -- Arvid Brodin | Consultant (Linux) XDIN AB | Jan Stenbecks Torg 17 | SE-164 40 Kista | Sweden | xdin.com