From 377cb248840907adc407324b4d23f97b3ee70c98 Mon Sep 17 00:00:00 2001 From: Florian Westphal Date: Thu, 10 Aug 2017 16:52:57 +0200 Subject: [PATCH] rtnetlink: use rcu_dereference_raw to silence rcu splat Ido reports a rcu splat in __rtnl_register. The splat is correct; as rtnl_register doesn't grab any logs and doesn't use rcu locks either. It has always been like this. handler families are not registered in parallel so there are no races wrt. the kmalloc ordering. The only reason to use rcu_dereference in the first place was to avoid sparse from complaining about this. Thus this switches to _raw() to not have rcu checks here. The alternative is to add rtnl locking to register/unregister, however, I don't see a compelling reason to do so as this has been lockless for the past twenty years or so. Fixes: 6853dd4881 ("rtnetlink: protect handler table with rcu") Reported-by: Ido Schimmel Signed-off-by: Florian Westphal Tested-by: Ido Schimmel Signed-off-by: David S. Miller --- net/core/rtnetlink.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c index dd4e50dfa248..a5bc5bd0dc12 100644 --- a/net/core/rtnetlink.c +++ b/net/core/rtnetlink.c @@ -172,7 +172,7 @@ int __rtnl_register(int protocol, int msgtype, BUG_ON(protocol < 0 || protocol > RTNL_FAMILY_MAX); msgindex = rtm_msgindex(msgtype); - tab = rcu_dereference(rtnl_msg_handlers[protocol]); + tab = rcu_dereference_raw(rtnl_msg_handlers[protocol]); if (tab == NULL) { tab = kcalloc(RTM_NR_MSGTYPES, sizeof(*tab), GFP_KERNEL); if (tab == NULL) -- 2.20.1