linux-kernel - Re: [PATCH 1/6] net: ip4_datagram_connect: Use correct form of statistics update

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Message-ID: <20131016083545.GP10651@twins.programming.kicks-ass.net>
Date:	Wed, 16 Oct 2013 10:35:45 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Christoph Lameter <cl@...ux.com>
Cc:	Tejun Heo <tj@...nel.org>, akpm@...uxfoundation.org,
	rostedt@...dmis.org, linux-kernel@...r.kernel.org,
	Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Eric Dumazet <edumazet@...gle.com>,
	David Miller <davem@...emloft.net>
Subject: Re: [PATCH 1/6] net: ip4_datagram_connect: Use correct form of
 statistics update

On Tue, Oct 15, 2013 at 12:47:23PM -0500, Christoph Lameter wrote:
> ip4_datagram_connect is called with BH processing enabled. Therefore
> we cannot use IP_INC_STATS_BH but must use IP_INC_STATS which disables
> BH handling before incrementing the counter.
> 
> The following trace is triggered without this patch:
> 
> [ 9293.806634] __this_cpu_add operation in preemptible [00000000] code: ntpd/2150

You lost the BUG there; that really needs to be there:

 - BUG makes people pay attention
 - This was an actual BUG wasn't it?

Sure there can be false positives, but in all cases people should amend
the code. Sometimes with a comment explaining why the raw primitive
should be used; sometimes to fix an actual bug, but a patch needs to be
written. Therefore BUG!
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