From af0fc14a4dca69503bf47b46f7b43eb6527019b3 Mon Sep 17 00:00:00 2001 From: Anders Roxell Date: Fri, 15 Nov 2019 11:24:30 +0100 Subject: [PATCH] net: ipmr: fix suspicious RCU warning When booting an arm64 allmodconfig kernel on linux-next (tag 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 introduces RCU locking around the problematic code path, that is function ipmr_rules_init() in ipmr_net_init(). Suggested-by: Paul E. McKenney Reviewed-by: Paul E. McKenney Signed-off-by: Anders Roxell --- net/ipv4/ipmr.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/net/ipv4/ipmr.c b/net/ipv4/ipmr.c index 6e68def66822..d207434c83af 100644 --- a/net/ipv4/ipmr.c +++ b/net/ipv4/ipmr.c @@ -3086,7 +3086,9 @@ static int __net_init ipmr_net_init(struct net *net) if (err) goto ipmr_notifier_fail; + rcu_read_lock(); err = ipmr_rules_init(net); + rcu_read_unlock(); if (err < 0) goto ipmr_rules_fail; -- 2.20.1