From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f194.google.com ([209.85.192.194]:42295 "EHLO mail-pf0-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933386AbeCGQnV (ORCPT ); Wed, 7 Mar 2018 11:43:21 -0500 Received: by mail-pf0-f194.google.com with SMTP id a16so1144428pfn.9 for ; Wed, 07 Mar 2018 08:43:20 -0800 (PST) Message-ID: <1520440999.109662.48.camel@gmail.com> Subject: [PATCH net-next] ip6mr: remove synchronize_rcu() in favor of SOCK_RCU_FREE From: Eric Dumazet To: Yuval Mintz , Kirill Tkhai Cc: "davem@davemloft.net" , "yoshfuji@linux-ipv6.org" , "netdev@vger.kernel.org" Date: Wed, 07 Mar 2018 08:43:19 -0800 In-Reply-To: <1520432537.109662.39.camel@gmail.com> References: <152035343583.28894.2225634076957704200.stgit@localhost.localdomain> <1520355021.109662.22.camel@gmail.com> <71411e21-0efa-0e41-836d-0301b1c1dbcb@virtuozzo.com> <1520432537.109662.39.camel@gmail.com> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: netdev-owner@vger.kernel.org List-ID: From: Eric Dumazet Kirill found that recently added synchronize_rcu() call in ip6mr_sk_done() was slowing down netns dismantle and posted a patch to use it only if the socket was found. I instead suggested to get rid of this call, and use instead SOCK_RCU_FREE We might later change IPv4 side to use the same technique and unify both stacks. IPv4 does not use synchronize_rcu() but has a call_rcu() that could be replaced by SOCK_RCU_FREE. Tested: time for i in {1..1000}; do unshare -n /bin/false;done Before : real 7m18.911s After : real 10.187s Fixes: 8571ab479a6e ("ip6mr: Make mroute_sk rcu-based") Signed-off-by: Eric Dumazet Reported-by: Kirill Tkhai Cc: Yuval Mintz ---  net/ipv6/ip6mr.c |    6 +++++-  1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/net/ipv6/ip6mr.c b/net/ipv6/ip6mr.c index 2a38f9de45d399fafc9f4bcc662b44be17279e51..7345bd6c4b7dda39c0d73d542e9ca9a5366542ff 100644 --- a/net/ipv6/ip6mr.c +++ b/net/ipv6/ip6mr.c @@ -1443,6 +1443,7 @@ static int ip6mr_sk_init(struct mr_table *mrt, struct sock *sk) err = -EADDRINUSE; } else { rcu_assign_pointer(mrt->mroute_sk, sk); + sock_set_flag(sk, SOCK_RCU_FREE); net->ipv6.devconf_all->mc_forwarding++; } write_unlock_bh(&mrt_lock); @@ -1472,6 +1473,10 @@ int ip6mr_sk_done(struct sock *sk) if (sk == rtnl_dereference(mrt->mroute_sk)) { write_lock_bh(&mrt_lock); RCU_INIT_POINTER(mrt->mroute_sk, NULL); + /* Note that mroute_sk had SOCK_RCU_FREE set, + * so the RCU grace period before sk freeing + * is guaranteed by sk_destruct() + */ net->ipv6.devconf_all->mc_forwarding--; write_unlock_bh(&mrt_lock); inet6_netconf_notify_devconf(net, RTM_NEWNETCONF, @@ -1485,7 +1490,6 @@ int ip6mr_sk_done(struct sock *sk) } } rtnl_unlock(); - synchronize_rcu(); return err; }