From mboxrd@z Thu Jan 1 00:00:00 1970 From: Stephen Hemminger Subject: Re: [RFC] net/hsr: Add support for IEC 62439-3 High-availability Seamless Redundancy Date: Thu, 24 May 2012 10:16:23 -0700 Message-ID: <20120524101623.16f09fea@nehalam.linuxnetplumber.net> References: <4F71BEAD.5080605@enea.com> <4FB14ADD.3050708@xdin.com> <20120514112821.526b12be@nehalam.linuxnetplumber.net> <4FBE6B5E.3060403@xdin.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Cc: "netdev@vger.kernel.org" , "David S. Miller" , Bruno Ferreira , Christian Borntraeger , Herbert Xu To: Arvid Brodin Return-path: Received: from mail.vyatta.com ([76.74.103.46]:59673 "EHLO mail.vyatta.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754966Ab2EXRQ1 (ORCPT ); Thu, 24 May 2012 13:16:27 -0400 In-Reply-To: <4FBE6B5E.3060403@xdin.com> Sender: netdev-owner@vger.kernel.org List-ID: On Thu, 24 May 2012 17:09:53 +0000 Arvid Brodin wrote: > On 2012-05-14 20:28, Stephen Hemminger wrote: > > On Mon, 14 May 2012 18:11:44 +0000 > > Arvid Brodin wrote: > > > >> 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.) > >> > > > > LLTX is deprecated (ie should not be used) for physical devices. > > > > Also, for virtual devices, there should be non transmit queue, this > > causes mulit-queue lockless semantics to be preserved as the call passes > > through the virtual device. > > (First: apologies for my late reply; your emails doesn't get through to me for some reason.) > > So does this mean that it is OK to use LLTX for virtual devices? My virtual device has > zero queue length (no transmit queue), but since it calls dev_queue_xmit for its slaves, I > still get recursive locking if I don't set LLTX (just like vlan and bonding does). Yes LLTX is fine for virtual devices.