[PATCH v2] net: ipmr: fix suspicious RCU warning
From: Anders Roxell
Date: Wed Nov 20 2019 - 10:23:11 EST
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@xxxxxxxxxxxxx>
Reviewed-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
Signed-off-by: Anders Roxell <anders.roxell@xxxxxxxxxx>
---
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