linux-kernel - Re: [PATCH] seqlock: fix raw_read_seqcount

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Message-ID: <20160525195745.GH3354@mtj.duckdns.org>
Date:	Wed, 25 May 2016 15:57:45 -0400
From:	Tejun Heo <tj@...nel.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Alexey Dobriyan <adobriyan@...il.com>, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org,
	Paul McKenney <paulmck@...ux.vnet.ibm.com>
Subject: Re: [PATCH] seqlock: fix raw_read_seqcount_latch()

Hello,

On Mon, May 23, 2016 at 11:36:18AM +0200, Peter Zijlstra wrote:
> > 	include/linux/percpu-refcount.h:146:36: warning: initialization makes pointer from integer without a cast [-Wint-conversion]
> > 	  percpu_ptr = lockless_dereference(ref->percpu_count_ptr);
> 
> TJ; would you prefer casting or not using lockless_dereference() here?

Casting is nasty - *(unsigned long __percpu **)& - because the macro
expects an lvalue.  I think it'd be better to revert to opencoding
READ_ONCE() and barrier there.  It's a pretty special case anyway.

Thanks.

-- 
tejun