Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758670Ab1DNCoI (ORCPT ); Wed, 13 Apr 2011 22:44:08 -0400 Received: from mga02.intel.com ([134.134.136.20]:56351 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758440Ab1DNCoH (ORCPT ); Wed, 13 Apr 2011 22:44:07 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.64,208,1301900400"; d="scan'208";a="628296987" Subject: Re: [patch v3 2/3] percpu_counter: fix code for 32bit systems for UP From: Shaohua Li To: Eric Dumazet Cc: "linux-kernel@vger.kernel.org" , "akpm@linux-foundation.org" , "tj@kernel.org" , "cl@linux.com" In-Reply-To: <1302748530.3549.24.camel@edumazet-laptop> References: <20110414020447.979946152@sli10-conroe.sh.intel.com> <20110414020747.201728372@sli10-conroe.sh.intel.com> <1302748530.3549.24.camel@edumazet-laptop> Content-Type: text/plain; charset="UTF-8" Date: Thu, 14 Apr 2011 10:44:04 +0800 Message-ID: <1302749044.3981.183.camel@sli10-conroe> Mime-Version: 1.0 X-Mailer: Evolution 2.30.3 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2031 Lines: 58 On Thu, 2011-04-14 at 10:35 +0800, Eric Dumazet wrote: > Le jeudi 14 avril 2011 à 10:04 +0800, shaohua.li@intel.com a écrit : > > pièce jointe document texte brut (percpu-counter-32bits.patch) > > percpu_counter.counter is a 's64'. Accessing it in 32-bit system is racing. > > we need some locking to protect it otherwise some very wrong value could be > > accessed. > > > > Signed-off-by: Shaohua Li > > --- > > include/linux/percpu_counter.h | 37 ++++++++++++++++++++++++++----------- > > 1 file changed, 26 insertions(+), 11 deletions(-) > > > > Index: linux/include/linux/percpu_counter.h > > =================================================================== > > --- linux.orig/include/linux/percpu_counter.h 2011-04-14 08:50:45.000000000 +0800 > > +++ linux/include/linux/percpu_counter.h 2011-04-14 09:09:14.000000000 +0800 > > @@ -89,9 +89,20 @@ struct percpu_counter { > > s64 count; > > }; > > > > -static inline int percpu_counter_init(struct percpu_counter *fbc, s64 amount) > > +static inline void percpu_counter_set(struct percpu_counter *fbc, s64 amount) > > { > > +#if BITS_PER_LONG == 32 > > + preempt_disable(); > > fbc->count = amount; > > + preempt_enable(); > > +#else > > + fbc->count = amount; > > +#endif > > +} > > + > > +static inline int percpu_counter_init(struct percpu_counter *fbc, s64 amount) > > +{ > > + percpu_counter_set(fbc, amount); > > return 0; > > } > > > > Please dont do this and obfuscate the code. > > percpu_counter_init() cannot be racy. > > Its like saying spin_lock_init() could be racy. > > No other thread/cpu is supposed to use the object if not yet > initialized. that's true. I just want the code looks consistent and this doesn't really obfuscate the code to me. Thanks, Shaohua -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/