Commit a366e300 authored Mar 07, 2018 by Eric Dumazet Committed by David S. Miller Mar 07, 2018

ip6mr: remove synchronize_rcu() in favor of SOCK_RCU_FREE



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: 8571ab47 ("ip6mr: Make mroute_sk rcu-based")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Kirill Tkhai <ktkhai@virtuozzo.com>
Cc: Yuval Mintz <yuvalm@mellanox.com>
Reviewed-by: Kirill Tkhai <ktkhai@virtuozzo.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent 3f6be0eb

net/ipv6/ip6mr.c

+5 −1

Original line number	Diff line number	Diff line
		@@ -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;
		}

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