From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jarek Poplawski Subject: Re: [PATCH] fib_trie: rcu_assign_pointer warning fix Date: Tue, 12 Feb 2008 08:57:14 +0000 Message-ID: <20080212085714.GB2582@ff.dom.local> References: <20080211.171645.74019568.davem@davemloft.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: shemminger@vyatta.com, paulmck@us.ibm.com, netdev@vger.kernel.org, linux-kernel@vger.kernel.org To: David Miller Return-path: Received: from ug-out-1314.google.com ([66.249.92.168]:49831 "EHLO ug-out-1314.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755504AbYBLIuC (ORCPT ); Tue, 12 Feb 2008 03:50:02 -0500 Received: by ug-out-1314.google.com with SMTP id z38so446070ugc.16 for ; Tue, 12 Feb 2008 00:50:00 -0800 (PST) Content-Disposition: inline In-Reply-To: <20080211.171645.74019568.davem@davemloft.net> Sender: netdev-owner@vger.kernel.org List-ID: On 12-02-2008 02:16, David Miller wrote: > From: Stephen Hemminger > Date: Mon, 11 Feb 2008 16:59:54 -0800 > > linux-kernel added to CC:, any change to generic kernel infrastructure > should be posted there > >> Eliminate warnings when rcu_assign_pointer is used with unsigned long. >> It is reasonable to use RCU with non-pointer values so allow it for general >> use. Add a comment to explain the if test. >> >> Signed-off-by: Stephen Hemminger >> --- >> include/linux/rcupdate.h | 13 +++++++------ >> 1 files changed, 7 insertions(+), 6 deletions(-) >> >> diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h >> index 37a642c..c44ac87 100644 >> --- a/include/linux/rcupdate.h >> +++ b/include/linux/rcupdate.h >> @@ -172,14 +172,15 @@ struct rcu_head { >> * structure after the pointer assignment. More importantly, this >> * call documents which pointers will be dereferenced by RCU read-side >> * code. >> + * >> + * If value is the NULL (constant 0), then no barrier is needed. >> */ >> >> -#define rcu_assign_pointer(p, v) \ >> - ({ \ >> - if (!__builtin_constant_p(v) || \ >> - ((v) != NULL)) \ >> - smp_wmb(); \ >> - (p) = (v); \ >> +#define rcu_assign_pointer(p, v) \ >> + ({ \ >> + if (!(__builtin_constant_p(v) && v)) \ ...But, "If value is the NULL (constant 0)" we have: if (!(1 && NULL != 0)) ==> if (!(0)) and the barrier is used?! >> + smp_wmb(); \ >> + (p) = (v); \ >> }) >> >> /** Regards, Jarek P.