From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ben Hutchings Subject: [PATCH net] ipv6: addrconf: Avoid calling netdevice notifiers with RCU read-side lock Date: Tue, 14 Aug 2012 19:54:51 +0100 Message-ID: <1344970491.2690.8.camel@bwh-desktop.uk.solarflarecom.com> References: <1344940096-5548-1-git-send-email-amwang@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Cc: , John Fastabend , Greg Rose , Thomas Graf , Eric Dumazet , Ben Hutchings , Cong Wang To: David Miller Return-path: Received: from webmail.solarflare.com ([12.187.104.25]:48950 "EHLO ocex02.SolarFlarecom.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1756069Ab2HNSy4 (ORCPT ); Tue, 14 Aug 2012 14:54:56 -0400 In-Reply-To: <1344940096-5548-1-git-send-email-amwang@redhat.com> Sender: netdev-owner@vger.kernel.org List-ID: Cong Wang reports that lockdep detected suspicious RCU usage while enabling IPV6 forwarding: [ 1123.310275] =============================== [ 1123.442202] [ INFO: suspicious RCU usage. ] [ 1123.558207] 3.6.0-rc1+ #109 Not tainted [ 1123.665204] ------------------------------- [ 1123.768254] include/linux/rcupdate.h:430 Illegal context switch in RCU read-side critical section! [ 1123.992320] [ 1123.992320] other info that might help us debug this: [ 1123.992320] [ 1124.307382] [ 1124.307382] rcu_scheduler_active = 1, debug_locks = 0 [ 1124.522220] 2 locks held by sysctl/5710: [ 1124.648364] #0: (rtnl_mutex){+.+.+.}, at: [] rtnl_trylock+0x15/0x17 [ 1124.882211] #1: (rcu_read_lock){.+.+.+}, at: [] rcu_lock_acquire+0x0/0x29 [ 1125.085209] [ 1125.085209] stack backtrace: [ 1125.332213] Pid: 5710, comm: sysctl Not tainted 3.6.0-rc1+ #109 [ 1125.441291] Call Trace: [ 1125.545281] [] lockdep_rcu_suspicious+0x109/0x112 [ 1125.667212] [] rcu_preempt_sleep_check+0x45/0x47 [ 1125.781838] [] __might_sleep+0x1e/0x19b [...] [ 1127.445223] [] call_netdevice_notifiers+0x4a/0x4f [...] [ 1127.772188] [] dev_disable_lro+0x32/0x6b [ 1127.885174] [] dev_forward_change+0x30/0xcb [ 1128.013214] [] addrconf_forward_change+0x85/0xc5 [...] addrconf_forward_change() uses RCU iteration over the netdev list, which is unnecessary since it already holds the RTNL lock. We also cannot reasonably require netdevice notifier functions not to sleep. Reported-by: Cong Wang Signed-off-by: Ben Hutchings --- net/ipv6/addrconf.c | 4 +--- 1 files changed, 1 insertions(+), 3 deletions(-) diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c index 7918181..6bc85f7 100644 --- a/net/ipv6/addrconf.c +++ b/net/ipv6/addrconf.c @@ -494,8 +494,7 @@ static void addrconf_forward_change(struct net *net, __s32 newf) struct net_device *dev; struct inet6_dev *idev; - rcu_read_lock(); - for_each_netdev_rcu(net, dev) { + for_each_netdev(net, dev) { idev = __in6_dev_get(dev); if (idev) { int changed = (!idev->cnf.forwarding) ^ (!newf); @@ -504,7 +503,6 @@ static void addrconf_forward_change(struct net *net, __s32 newf) dev_forward_change(idev); } } - rcu_read_unlock(); } static int addrconf_fixup_forwarding(struct ctl_table *table, int *p, int newf) -- 1.7.7.6 -- Ben Hutchings, Staff Engineer, Solarflare Not speaking for my employer; that's the marketing department's job. They asked us to note that Solarflare product names are trademarked.