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

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Message-ID: <aLjFWzreiLM8nWgL@strlen.de>
Date: Thu, 4 Sep 2025 00:52:20 +0200
From: Florian Westphal <fw@...len.de>
To: Jakub Kicinski <kuba@...nel.org>
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

Jakub Kicinski <kuba@...nel.org> wrote:
> 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?

That works too.  I'll send a new PR tomorrow, its late here.