Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756719Ab0DUVps (ORCPT ); Wed, 21 Apr 2010 17:45:48 -0400 Received: from e5.ny.us.ibm.com ([32.97.182.145]:47846 "EHLO e5.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755232Ab0DUVpq (ORCPT ); Wed, 21 Apr 2010 17:45:46 -0400 Date: Wed, 21 Apr 2010 14:45:42 -0700 From: "Paul E. McKenney" To: Borislav Petkov , Miles Lane , Eric Paris , Lai Jiangshan , Ingo Molnar , Peter Zijlstra , LKML Cc: eric.dumazet@gmail.com, netdev@vger.kernel.org Subject: Re: [PATCH] RCU: don't turn off lockdep when find suspicious rcu_dereference_check() usage Message-ID: <20100421214542.GP2563@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <1271701612.2972.5.camel@dhcp231-113.rdu.redhat.com> <20100419230136.GA16856@linux.vnet.ibm.com> <1271726729.2972.13.camel@dhcp231-113.rdu.redhat.com> <20100420030452.GB2905@linux.vnet.ibm.com> <4BCD646B.1080206@cn.fujitsu.com> <1271766716.2972.16.camel@dhcp231-113.rdu.redhat.com> <20100420135227.GC2628@linux.vnet.ibm.com> <20100421060428.GA3839@liondog.tnic> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20100421060428.GA3839@liondog.tnic> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4909 Lines: 97 On Wed, Apr 21, 2010 at 08:04:28AM +0200, Borislav Petkov wrote: > Hi, > > a plain -rc5 triggers at net/core/dev.c:1993 here too: Thank you for testing this, Borislav! A prototype patch may be found below, CCing the netdev guys for their thoughts on this. (And if this patch is valid, it is probably best for it to go up with the networking patches, since this part of the code looks to be under active development.) Thanx, Paul > [ 12.889090] =================================================== > [ 12.889387] [ INFO: suspicious rcu_dereference_check() usage. ] > [ 12.889533] --------------------------------------------------- > [ 12.889679] net/core/dev.c:1993 invoked rcu_dereference_check() without protection! > [ 12.889929] > [ 12.889929] other info that might help us debug this: > [ 12.889930] > [ 12.890368] > [ 12.890369] rcu_scheduler_active = 1, debug_locks = 0 > [ 12.890659] 2 locks held by swapper/0: > [ 12.890803] #0: (&idev->mc_ifc_timer){+.-...}, at: [] run_timer_softirq+0x266/0x503 > [ 12.891227] #1: (rcu_read_lock_bh){.+....}, at: [] dev_queue_xmit+0x153/0x512 > [ 12.891647] > [ 12.891648] stack backtrace: > [ 12.891934] Pid: 0, comm: swapper Not tainted 2.6.34-rc5 #1 > [ 12.892085] Call Trace: > [ 12.892231] [] lockdep_rcu_dereference+0xaa/0xb2 > [ 12.892430] [] dev_queue_xmit+0x25e/0x512 > [ 12.892576] [] ? dev_queue_xmit+0x153/0x512 > [ 12.892723] [] ? trace_hardirqs_on+0xd/0xf > [ 12.892871] [] ? local_bh_enable_ip+0xbc/0xda > [ 12.893024] [] neigh_resolve_output+0x323/0x36a > [ 12.893183] [] ? ipv6_chk_mcast_addr+0x0/0x1fa [ipv6] > [ 12.893338] [] ip6_output_finish+0x81/0xb9 [ipv6] > [ 12.893492] [] ip6_output2+0x2a9/0x2b4 [ipv6] > [ 12.893644] [] ip6_output+0xbc1/0xbd0 [ipv6] > [ 12.893797] [] ? fib6_force_start_gc+0x30/0x32 [ipv6] > [ 12.893951] [] mld_sendpack+0x30b/0x435 [ipv6] > [ 12.894109] [] ? mld_sendpack+0x0/0x435 [ipv6] > [ 12.894264] [] ? mark_held_locks+0x52/0x70 > [ 12.894418] [] mld_ifc_timer_expire+0x254/0x28d [ipv6] > [ 12.894570] [] run_timer_softirq+0x381/0x503 > [ 12.894717] [] ? run_timer_softirq+0x266/0x503 > [ 12.894870] [] ? mld_ifc_timer_expire+0x0/0x28d [ipv6] > [ 12.895024] [] ? __do_softirq+0x79/0x2f5 > [ 12.895174] [] __do_softirq+0x180/0x2f5 > [ 12.895323] [] call_softirq+0x1c/0x28 > [ 12.895472] [] do_softirq+0x3d/0x85 > [ 12.895619] [] irq_exit+0x4a/0x95 > [ 12.895766] [] smp_apic_timer_interrupt+0x8c/0x9a > [ 12.895913] [] apic_timer_interrupt+0x13/0x20 > [ 12.896065] [] ? _raw_spin_unlock_irqrestore+0x38/0x69 > [ 12.896363] [] ? default_idle+0xd8/0x10a > [ 12.896512] [] ? default_idle+0xd6/0x10a > [ 12.896658] [] c1e_idle+0xcd/0xf4 > [ 12.896805] [] cpu_idle+0x5e/0xb5 > [ 12.896952] [] rest_init+0xff/0x106 > [ 12.897104] [] ? rest_init+0x0/0x106 > [ 12.897260] [] start_kernel+0x30f/0x31a > [ 12.897409] [] x86_64_start_reservations+0x7d/0x81 > [ 12.897560] [] x86_64_start_kernel+0xe4/0xeb commit df3f17af2d26d1451a3d23d5c7b7a6423a38569e Author: Paul E. McKenney Date: Wed Apr 21 14:40:37 2010 -0700 net: fix dev_pick_tx() to use rcu_dereference_bh() dev_pick_tx() is called in an RCU-bh read-side critical section, but uses rcu_dereference(). This patch changes to rcu_dereference_bh() in order to suppress the RCU lockdep splat. Signed-off-by: Paul E. McKenney diff --git a/net/core/dev.c b/net/core/dev.c index 92584bf..f769098 100644 --- a/net/core/dev.c +++ b/net/core/dev.c @@ -1990,7 +1990,7 @@ static struct netdev_queue *dev_pick_tx(struct net_device *dev, queue_index = skb_tx_hash(dev, skb); if (sk) { - struct dst_entry *dst = rcu_dereference(sk->sk_dst_cache); + struct dst_entry *dst = rcu_dereference_bh(sk->sk_dst_cache); if (dst && skb_dst(skb) == dst) sk_tx_queue_set(sk, queue_index); -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/