From mboxrd@z Thu Jan  1 00:00:00 1970
From: Arun Sharma <asharma@fb.com>
Subject: Re: Kernel crash after using new Intel NIC (igb)
Date: Fri, 27 May 2011 10:52:22 -0700
Message-ID: <4DDFE4D6.4010000@fb.com>
References: <201104250033.03401.maxi@daemonizer.de>	 <1303878240.2699.41.camel@edumazet-laptop>	 <1303878771.2699.44.camel@edumazet-laptop>	 <201104271352.00601.maxi@daemonizer.de>	 <20110512211033.GA3468@dev1756.snc6.facebook.com>	 <1305234953.2831.2.camel@edumazet-laptop>	 <20110524213327.GA3917@dev1756.snc6.facebook.com>	 <1306291469.3305.11.camel@edumazet-laptop>	 <20110525060609.GA32244@dev1756.snc6.facebook.com>	 <1306305331.3305.22.camel@edumazet-laptop>  <4DDEAA3C.7020502@fb.com>	 <1306439246.2543.10.camel@edumazet-laptop>  <4DDECA9B.8080206@fb.com>	 <1306447292.2543.32.camel@edumazet-laptop>  <4DDEEBC5.80804@fb.com> <1306466831.2543.58.camel@edumazet-laptop>
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Cc: David Miller <davem@davemloft.net>,
	Maximilian Engelhardt <maxi@daemonizer.de>,
	linux-kernel@vger.kernel.org, netdev@vger.kernel.org,
	StuStaNet Vorstand <vorstand@stusta.mhn.de>,
	Yann Dupont <Yann.Dupont@univ-nantes.fr>,
	Denys Fedoryshchenko <denys@visp.net.lb>
To: Eric Dumazet <eric.dumazet@gmail.com>
Return-path: <linux-kernel-owner@vger.kernel.org>
In-Reply-To: <1306466831.2543.58.camel@edumazet-laptop>
Sender: linux-kernel-owner@vger.kernel.org
List-Id: netdev.vger.kernel.org

On 5/26/11 8:27 PM, Eric Dumazet wrote:

Looks good. Thanks for taking care of this.

> +static bool atomic_add_unless_return(atomic_t *ptr, int a, int u, int *newv)
> +{
> +	int cur, old = atomic_read(ptr);
> +
> +	while (old != u) {
> +		*newv = old + a;
> +		cur = atomic_cmpxchg(ptr, old, *newv);
> +		if (cur == old)
> +			return true;
> +		old = cur;
> +	}
> +	return false;
> +}

This looks very similar to atomic_add_unless(). If we had a

__atomic_add_unless() that returned "old", we could then do:

atomic_add_unless() { return __atomic_add_unless() != u }
atomic_add_unless_return() { return __atomic_add_unless() + a}

  -Arun