netdev - Re: [PATCH net 1/2] selftests: netfilter: fix udpclash tool hang

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Message-ID: <20250903151554.5c72661e@kernel.org>
Date: Wed, 3 Sep 2025 15:15:54 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Florian Westphal <fw@...len.de>
Cc: <netdev@...r.kernel.org>, Paolo Abeni <pabeni@...hat.com>, "David S.
 Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 <netfilter-devel@...r.kernel.org>, pablo@...filter.org
Subject: Re: [PATCH net 1/2] selftests: netfilter: fix udpclash tool hang

On Tue,  2 Sep 2025 20:58:54 +0200 Florian Westphal wrote:
> Yi Chen reports that 'udpclash' loops forever depending on compiler
> (and optimization level used); while (x == 1) gets optimized into
> for (;;).  Switch to stdatomic to prevent this.

gcc version 15.1.1 (F42) w/ whatever flags kselftests use appear to be
unaware of this macro:

udpclash.c:33:26: error: implicit declaration of function ‘ATOMIC_VAR_INIT’; did you mean ‘ATOMIC_FLAG_INIT’? [-Wimplicit-function-declaration]
   33 | static atomic_int wait = ATOMIC_VAR_INIT(1);
      |                          ^~~~~~~~~~~~~~~
      |                          ATOMIC_FLAG_INIT
udpclash.c:33:26: error: initializer element is not constant

Could you perhaps use volatile instead?

> +#include <stdatomic.h>
>  #include <stdio.h>
>  #include <string.h>
>  #include <stdlib.h>
> @@ -29,7 +30,7 @@ struct thread_args {
>  	int sockfd;
>  };
>  
> -static int wait = 1;
> +static atomic_int wait = ATOMIC_VAR_INIT(1);
>  
>  static void *thread_main(void *varg)
>  {