netdev - Re: [PATCH net 2/2] net: Flush deferred skb free on socket destroy

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Date:   Sun, 23 Jan 2022 10:50:49 +0100
From:   Heiko Carstens <hca@...ux.ibm.com>
To:     Gal Pressman <gal@...dia.com>
Cc:     Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
        Tariq Toukan <tariqt@...dia.com>,
        Saeed Mahameed <saeedm@...dia.com>
Subject: Re: [PATCH net 2/2] net: Flush deferred skb free on socket destroy

On Mon, Jan 17, 2022 at 11:27:33AM +0200, Gal Pressman wrote:
> The cited Fixes patch moved to a deferred skb approach where the skbs
> are not freed immediately under the socket lock.  Add a WARN_ON_ONCE()
> to verify the deferred list is empty on socket destroy, and empty it to
> prevent potential memory leaks.
> 
> Fixes: f35f821935d8 ("tcp: defer skb freeing after socket lock is released")
> Signed-off-by: Gal Pressman <gal@...dia.com>
> ---
>  net/core/sock.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/net/core/sock.c b/net/core/sock.c
> index f32ec08a0c37..4ff806d71921 100644
> --- a/net/core/sock.c
> +++ b/net/core/sock.c
> @@ -2049,6 +2049,9 @@ void sk_destruct(struct sock *sk)
>  {
>  	bool use_call_rcu = sock_flag(sk, SOCK_RCU_FREE);
>  
> +	WARN_ON_ONCE(!llist_empty(&sk->defer_list));
> +	sk_defer_free_flush(sk);
> +

This leads to a link error if CONFIG_INET is not set:

s390x-11.2.0-ld: net/core/sock.o: in function `sk_defer_free_flush':
linux/./include/net/tcp.h:1378: undefined reference to `__sk_defer_free_flush'
make: *** [Makefile:1155: vmlinux] Error 1