netdev - Re: [PATCH 02/36] scsi,rcu: convert call_rcu(fc_rport_free_rcu) to kfree

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Message-ID: <20110323231948.GE13806@parisc-linux.org>
Date:	Wed, 23 Mar 2011 17:19:49 -0600
From:	Matthew Wilcox <matthew@....cx>
To:	James Bottomley <James.Bottomley@...e.de>
Cc:	paulmck@...ux.vnet.ibm.com, Robert Love <robert.w.love@...el.com>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	Ingo Molnar <mingo@...e.hu>, Jens Axboe <axboe@...nel.dk>,
	Neil Horman <nhorman@...driver.com>,
	"David S. Miller" <davem@...emloft.net>,
	Alexey Kuznetsov <kuznet@....inr.ac.ru>,
	"Pekka Savola (ipv6)" <pekkas@...core.fi>,
	James Morris <jmorris@...ei.org>,
	Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
	Patrick McHardy <kaber@...sh.net>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Stephen Hemminger <shemminger@...tta.com>,
	Tejun Heo <tj@...nel.org>, Jarek Poplawski <jarkao2@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devel@...n-fcoe.org" <devel@...n-fcoe.org>,
	"linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH 02/36] scsi,rcu: convert call_rcu(fc_rport_free_rcu) to
	kfree_rcu()

On Wed, Mar 23, 2011 at 09:05:51AM -0500, James Bottomley wrote:
> > #define kfree_rcu(ptr, rcu_head)					\
> > 	__kfree_rcu(&((ptr)->rcu_head), offsetof(typeof(*(ptr)), rcu_head))
> 
> Isn't this one of those cases where the obvious use of the interface is
> definitely wrong?

But it's a compile time breakage if you use it wrong, not runtime.

> It's also another nasty pseudo C prototype.  I know we do this sort of
> thing for container_of et al, but I don't really think we want to extend
> it.

We do it for list_entry, list_for_each_entry, etc.  And those are very
widespread within the kernel.

-- 
Matthew Wilcox				Intel Open Source Technology Centre
"Bill, look, we understand that you're interested in selling us this
operating system, but compare it to ours.  We can't possibly take such
a retrograde step."
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