Subject: Re: [PATCH net-next] tcp: Fix tcp_syn_flood_action() if CONFIG_IPV6=n

From: Jakub Kicinski <[email-masked]>
Date: Wed, 16 Nov 2022 12:31:15 -0800

On Tue, 15 Nov 2022 11:12:16 +0100 Geert Uytterhoeven wrote:
> If CONFIG_IPV6=n:
> 
>     net/ipv4/tcp_input.c: In function ‘tcp_syn_flood_action’:
>     include/net/sock.h:387:37: error: ‘const struct sock_common’ has no member named ‘skc_v6_rcv_saddr’; did you mean ‘skc_rcv_saddr’?
>       387 | #define sk_v6_rcv_saddr __sk_common.skc_v6_rcv_saddr
> 	  |                                     ^~~~~~~~~~~~~~~~
>     include/linux/printk.h:429:19: note: in definition of macro ‘printk_index_wrap’
>       429 |   _p_func(_fmt, ##__VA_ARGS__);    \
> 	  |                   ^~~~~~~~~~~
>     include/linux/printk.h:530:2: note: in expansion of macro ‘printk’
>       530 |  printk(KERN_INFO pr_fmt(fmt), ##__VA_ARGS__)
> 	  |  ^~~~~~
>     include/linux/net.h:272:3: note: in expansion of macro ‘pr_info’
>       272 |   function(__VA_ARGS__);    \
> 	  |   ^~~~~~~~
>     include/linux/net.h:288:2: note: in expansion of macro ‘net_ratelimited_function’
>       288 |  net_ratelimited_function(pr_info, fmt, ##__VA_ARGS__)
> 	  |  ^~~~~~~~~~~~~~~~~~~~~~~~
>     include/linux/net.h:288:43: note: in expansion of macro ‘sk_v6_rcv_saddr’
>       288 |  net_ratelimited_function(pr_info, fmt, ##__VA_ARGS__)
> 	  |                                           ^~~~~~~~~~~
>     net/ipv4/tcp_input.c:6847:4: note: in expansion of macro ‘net_info_ratelimited’
>      6847 |    net_info_ratelimited("%s: Possible SYN flooding on port [%pI6c]:%u. %s.\n",
> 	  |    ^~~~~~~~~~~~~~~~~~~~
> 
> Fix this by using "#if" instead of "if", like is done for all other
> checks for CONFIG_IPV6.
> 
> Fixes: d9282e48c6088105 ("tcp: Add listening address to SYN flood message")
> Signed-off-by: Geert Uytterhoeven <[email-masked]>

Sorry for the late reaction, this now conflicts with bf36267e3ad3df8

I was gonna hand edit but perhaps we can do better with the ifdef
formation.

Instead of 

#ifdef v6
	if (v6) {
		expensive_call6();
	} else    //  d k
#endif            //  o i
	{         //  o e
		expensive_call4();
	}

Can we go with:

#ifdef v6
	if (v6)
		expensive_call6();
	else 
#endif
		expensive_call4();

or

	if (v4) {
		expensive_call4();
#ifdef v6
	} else {
		expensive_call6();
#endif
	}

or

	if (v6) {
#ifdef v6
		expensive_call6();
#endif
	} else {
		expensive_call6();
	}

I know you're just going with the most obviously correct / smallest diff
way, but the broken up else bracket gives me flashbacks of looking at
vendor code :S