Subject: Re: [PATCH 02/36] scsi,rcu: convert call_rcu(fc_rport_free_rcu) to
 kfree_rcu()
From: James Bottomley <James.Bottomley@suse.de>
To: paulmck@linux.vnet.ibm.com
Cc: Robert Love <robert.w.love@intel.com>,
        Lai Jiangshan <laijs@cn.fujitsu.com>, Ingo Molnar <mingo@elte.hu>,
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        Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>,
        "Pekka Savola (ipv6)" <pekkas@netcore.fi>,
        James Morris <jmorris@namei.org>,
        Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>,
        Patrick McHardy <kaber@trash.net>,
        Eric Dumazet <eric.dumazet@gmail.com>,
        Stephen Hemminger <shemminger@vyatta.com>, Tejun Heo <tj@kernel.org>,
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Date: Wed, 23 Mar 2011 09:05:51 -0500
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On Tue, 2011-03-22 at 23:50 -0700, Paul E. McKenney wrote:
> The kfree_rcu() definition is as
> follows:
> 
> #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?

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.

Why not make the interface take a pointer to the embedding structure and
one to the rcu_head ... that way all pointer mathematics can be
contained inside the RCU routines.

James


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