Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753324Ab1DRHll (ORCPT ); Mon, 18 Apr 2011 03:41:41 -0400 Received: from mga02.intel.com ([134.134.136.20]:8820 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751246Ab1DRHle (ORCPT ); Mon, 18 Apr 2011 03:41:34 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.64,231,1301900400"; d="scan'208";a="630362121" 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: <1302749677.3549.26.camel@edumazet-laptop> References: <20110414020447.979946152@sli10-conroe.sh.intel.com> <20110414020747.201728372@sli10-conroe.sh.intel.com> <1302748530.3549.24.camel@edumazet-laptop> <1302749044.3981.183.camel@sli10-conroe> <1302749677.3549.26.camel@edumazet-laptop> Content-Type: text/plain; charset="UTF-8" Date: Mon, 18 Apr 2011 15:41:32 +0800 Message-ID: <1303112492.3981.189.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: 2641 Lines: 91 On Thu, 2011-04-14 at 10:54 +0800, Eric Dumazet wrote: > Le jeudi 14 avril 2011 à 10:44 +0800, Shaohua Li a écrit : > > that's true. I just want the code looks consistent and this doesn't > > really obfuscate the code to me. > > Doing so gives a false sense of security to user. > > percpu_counter_init() is unsafe by nature. I really don't think this matters, but since you insist, here is the updated the patch. Subject: percpu_counter: fix code for 32bit systems for UP 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 | 31 +++++++++++++++++++++++-------- 1 file changed, 23 insertions(+), 8 deletions(-) Index: linux/include/linux/percpu_counter.h =================================================================== --- linux.orig/include/linux/percpu_counter.h 2011-04-18 15:36:31.000000000 +0800 +++ linux/include/linux/percpu_counter.h 2011-04-18 15:37:35.000000000 +0800 @@ -101,14 +101,34 @@ static inline void percpu_counter_destro 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 s64 percpu_counter_read(struct percpu_counter *fbc) +{ +#if BITS_PER_LONG == 32 + s64 count; + preempt_disable(); + count = fbc->count; + preempt_enable(); + return count; +#else + return fbc->count; +#endif } static inline int percpu_counter_compare(struct percpu_counter *fbc, s64 rhs) { - if (fbc->count > rhs) + s64 count = percpu_counter_read(fbc); + if (count > rhs) return 1; - else if (fbc->count < rhs) + else if (count < rhs) return -1; else return 0; @@ -128,18 +148,13 @@ __percpu_counter_add(struct percpu_count percpu_counter_add(fbc, amount); } -static inline s64 percpu_counter_read(struct percpu_counter *fbc) -{ - return fbc->count; -} - /* * percpu_counter is intended to track positive number. In UP case, the number * should never be negative. */ static inline s64 percpu_counter_read_positive(struct percpu_counter *fbc) { - return fbc->count; + return percpu_counter_read(fbc); } static inline s64 percpu_counter_sum_positive(struct percpu_counter *fbc) -- 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/