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Date: Wed, 20 Nov 2019 16:22:55 +0100 From: Anders Roxell <anders.roxell@...aro.org> To: davem@...emloft.net, kuznet@....inr.ac.ru, yoshfuji@...ux-ipv6.org Cc: paulmck@...nel.org, netdev@...r.kernel.org, linux-kernel@...r.kernel.org, Anders Roxell <anders.roxell@...aro.org> Subject: [PATCH v2] net: ipmr: fix suspicious RCU warning When booting an arm64 allmodconfig kernel on linux-next next-20191115 The following "suspicious RCU usage" warning shows up. This bug seems to have been introduced by commit f0ad0860d01e ("ipv4: ipmr: support multiple tables") in 2010, but the warning was added only in this past year by commit 28875945ba98 ("rcu: Add support for consolidated-RCU reader checking"). [ 32.496021][ T1] ============================= [ 32.497616][ T1] WARNING: suspicious RCU usage [ 32.499614][ T1] 5.4.0-rc6-next-20191108-00003-gf74bac957b5c-dirty #2 Not tainted [ 32.502018][ T1] ----------------------------- [ 32.503976][ T1] net/ipv4/ipmr.c:136 RCU-list traversed in non-reader section!! [ 32.506746][ T1] [ 32.506746][ T1] other info that might help us debug this: [ 32.506746][ T1] [ 32.509794][ T1] [ 32.509794][ T1] rcu_scheduler_active = 2, debug_locks = 1 [ 32.512661][ T1] 1 lock held by swapper/0/1: [ 32.514169][ T1] #0: ffffa000150dd678 (pernet_ops_rwsem){+.+.}, at: register_pernet_subsys+0x24/0x50 [ 32.517621][ T1] [ 32.517621][ T1] stack backtrace: [ 32.519930][ T1] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.4.0-rc6-next-20191108-00003-gf74bac957b5c-dirty #2 [ 32.523063][ T1] Hardware name: linux,dummy-virt (DT) [ 32.524787][ T1] Call trace: [ 32.525946][ T1] dump_backtrace+0x0/0x2d0 [ 32.527433][ T1] show_stack+0x20/0x30 [ 32.528811][ T1] dump_stack+0x204/0x2ac [ 32.530258][ T1] lockdep_rcu_suspicious+0xf4/0x108 [ 32.531993][ T1] ipmr_get_table+0xc8/0x170 [ 32.533496][ T1] ipmr_new_table+0x48/0xa0 [ 32.535002][ T1] ipmr_net_init+0xe8/0x258 [ 32.536465][ T1] ops_init+0x280/0x2d8 [ 32.537876][ T1] register_pernet_operations+0x210/0x420 [ 32.539707][ T1] register_pernet_subsys+0x30/0x50 [ 32.541372][ T1] ip_mr_init+0x54/0x180 [ 32.542785][ T1] inet_init+0x25c/0x3e8 [ 32.544186][ T1] do_one_initcall+0x4c0/0xad8 [ 32.545757][ T1] kernel_init_freeable+0x3e0/0x500 [ 32.547443][ T1] kernel_init+0x14/0x1f0 [ 32.548875][ T1] ret_from_fork+0x10/0x18 This commit therefore holds RTNL mutex around the problematic code path, which is function ipmr_rules_init() in ipmr_net_init(). This commit also adds a lockdep_rtnl_is_held() check to the ipmr_for_each_table() macro. Suggested-by: David Miller <davem@...emloft.net> Reviewed-by: Paul E. McKenney <paulmck@...nel.org> Signed-off-by: Anders Roxell <anders.roxell@...aro.org> --- net/ipv4/ipmr.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/net/ipv4/ipmr.c b/net/ipv4/ipmr.c index 6e68def66822..53dff9a0e60a 100644 --- a/net/ipv4/ipmr.c +++ b/net/ipv4/ipmr.c @@ -110,7 +110,8 @@ static void ipmr_expire_process(struct timer_list *t); #ifdef CONFIG_IP_MROUTE_MULTIPLE_TABLES #define ipmr_for_each_table(mrt, net) \ - list_for_each_entry_rcu(mrt, &net->ipv4.mr_tables, list) + list_for_each_entry_rcu(mrt, &net->ipv4.mr_tables, list, \ + lockdep_rtnl_is_held()) static struct mr_table *ipmr_mr_table_iter(struct net *net, struct mr_table *mrt) @@ -3086,7 +3087,9 @@ static int __net_init ipmr_net_init(struct net *net) if (err) goto ipmr_notifier_fail; + rtnl_lock(); err = ipmr_rules_init(net); + rtnl_unlock(); if (err < 0) goto ipmr_rules_fail; -- 2.20.1
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