On 07.03.2018 19:43, Eric Dumazet wrote:
> 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
Reviewed-by: Kirill Tkhai
> ---
> 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;
> }
>
