Re: [PATCH net-next] tcp: use 2-arg optimal variant of kfree_rcu()

["Paul E. McKenney" <paulmck@kernel.org>]

On Fri, Dec 02, 2022 at 05:28:47AM +0000, Eric Dumazet wrote:
> kfree_rcu(1-arg) should be avoided as much as possible,
> since this is only possible from sleepable contexts,
> and incurr extra rcu barriers.
> 
> I wish the 1-arg variant of kfree_rcu() would
> get a distinct name, like kfree_rcu_slow()
> to avoid it being abused.

Fair point, the bug of forgetting the second argument goes unflagged,
at least from contexts where blocking is OK.

Let the bikeshedding commence!  ;-)

							Thanx, Paul

> Fixes: 459837b522f7 ("net/tcp: Disable TCP-MD5 static key on tcp_md5sig_info destruction")
> Signed-off-by: Eric Dumazet <edumazet@google.com>
> Cc: Dmitry Safonov <dima@arista.com>
> Cc: Paul E. McKenney <paulmck@kernel.org>
> ---
>  net/ipv4/tcp_ipv4.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
> index 7fae586405cfb10011a0674289280bf400dfa8d8..8320d0ecb13ae1e3e259f3c13a4c2797fbd984a5 100644
> --- a/net/ipv4/tcp_ipv4.c
> +++ b/net/ipv4/tcp_ipv4.c
> @@ -1245,7 +1245,7 @@ int tcp_md5_do_add(struct sock *sk, const union tcp_md5_addr *addr,
>  
>  			md5sig = rcu_dereference_protected(tp->md5sig_info, lockdep_sock_is_held(sk));
>  			rcu_assign_pointer(tp->md5sig_info, NULL);
> -			kfree_rcu(md5sig);
> +			kfree_rcu(md5sig, rcu);
>  			return -EUSERS;
>  		}
>  	}
> @@ -1271,7 +1271,7 @@ int tcp_md5_key_copy(struct sock *sk, const union tcp_md5_addr *addr,
>  			md5sig = rcu_dereference_protected(tp->md5sig_info, lockdep_sock_is_held(sk));
>  			net_warn_ratelimited("Too many TCP-MD5 keys in the system\n");
>  			rcu_assign_pointer(tp->md5sig_info, NULL);
> -			kfree_rcu(md5sig);
> +			kfree_rcu(md5sig, rcu);
>  			return -EUSERS;
>  		}
>  	}
> -- 
> 2.39.0.rc0.267.gcb52ba06e7-goog
>