Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1764551AbZDAROR (ORCPT ); Wed, 1 Apr 2009 13:14:17 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1761834AbZDARNy (ORCPT ); Wed, 1 Apr 2009 13:13:54 -0400 Received: from gw1.cosmosbay.com ([212.99.114.194]:52071 "EHLO gw1.cosmosbay.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759533AbZDARNx convert rfc822-to-8bit (ORCPT ); Wed, 1 Apr 2009 13:13:53 -0400 Message-ID: <49D3A0C2.9000403@cosmosbay.com> Date: Wed, 01 Apr 2009 19:13:38 +0200 From: Eric Dumazet User-Agent: Thunderbird 2.0.0.21 (Windows/20090302) MIME-Version: 1.0 To: Ingo Molnar CC: Jeremy Fitzhardinge , Tejun Heo , linux kernel , Linux Netdev List , Joe Perches , Rusty Russell Subject: Re: [PATCH] x86: percpu_to_op() misses memory and flags clobbers References: <49D32212.80607@cosmosbay.com> <49D32DC2.9010003@goop.org> <49D33E80.70802@cosmosbay.com> <20090401161218.GB3859@elte.hu> In-Reply-To: <20090401161218.GB3859@elte.hu> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-1.6 (gw1.cosmosbay.com [0.0.0.0]); Wed, 01 Apr 2009 19:13:39 +0200 (CEST) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4165 Lines: 130 Ingo Molnar a ?crit : > * Eric Dumazet wrote: > >> Jeremy Fitzhardinge a ?crit : >>> Eric Dumazet wrote: >>>> While playing with new percpu_{read|write|add|sub} stuff in network tree, >>>> I found x86 asm was a litle bit optimistic. >>>> >>>> We need to tell gcc that percpu_{write|add|sub|or|xor} are modyfing >>>> memory and possibly eflags. We could add another parameter to >>>> percpu_to_op() >>>> to separate the plain "mov" case (not changing eflags), >>>> but let keep it simple for the moment. >>>> >>> Did you observe an actual failure that this patch fixed? >>> >> Not in current tree, as we dont use yet percpu_xxxx() very much. >> >> If deployed for SNMP mibs with hundred of call sites, >> can you guarantee it will work as is ? > > Do we "guarantee" it for you? No. > > Is it expected to work just fine? Yes. > > Are there any known bugs in this area? No. Good to know. So I shut up. I am a jerk and should blindly trust linux kernel, sorry. > > Will we fix it if it's demonstrated to be broken? Of course! :-) > > [ Btw., it's definitely cool that you will make heavy use for it for > SNMP mib statistics - please share with us your experiences with > the facilities - good or bad experiences alike! ] I tried but I miss kind of an indirect percpu_add() function. because of Net namespaces, mibs are dynamically allocated, and current percpu_add() works on static percpu only (because of added per_cpu__ prefix) #define percpu_add(var, val) percpu_to_op("add", per_cpu__##var, val) I tried adding : #define dyn_percpu_add(var, val) percpu_to_op("add", var, val) But I dont know it this is the plan ? Should we get rid of "per_cpu__" prefix and use a special ELF section/ marker instead ? I have a patch to add percpu_inc() and percpu_dec(), I am not sure its worth it... [PATCH] percpu: Adds percpu_inc() and percpu_dec() Increments and decrements are quite common operations for SNMP mibs. Signed-off-by: Eric Dumazet diff --git a/arch/x86/include/asm/percpu.h b/arch/x86/include/asm/percpu.h index aee103b..248be11 100644 --- a/arch/x86/include/asm/percpu.h +++ b/arch/x86/include/asm/percpu.h @@ -103,6 +103,29 @@ do { \ } \ } while (0) +#define percpu_to_op0(op, var) \ +do { \ + switch (sizeof(var)) { \ + case 1: \ + asm(op "b "__percpu_arg(0) \ + : "+m" (var)); \ + break; \ + case 2: \ + asm(op "w "__percpu_arg(0) \ + : "+m" (var)); \ + break; \ + case 4: \ + asm(op "l "__percpu_arg(0) \ + : "+m" (var)); \ + break; \ + case 8: \ + asm(op "q "__percpu_arg(0) \ + : "+m" (var)); \ + break; \ + default: __bad_percpu_size(); \ + } \ +} while (0) + #define percpu_from_op(op, var) \ ({ \ typeof(var) ret__; \ @@ -139,6 +162,8 @@ do { \ #define percpu_and(var, val) percpu_to_op("and", per_cpu__##var, val) #define percpu_or(var, val) percpu_to_op("or", per_cpu__##var, val) #define percpu_xor(var, val) percpu_to_op("xor", per_cpu__##var, val) +#define percpu_inc(var) percpu_to_op0("inc", per_cpu__##var) +#define percpu_dec(var) percpu_to_op0("dec", per_cpu__##var) /* This is not atomic against other CPUs -- CPU preemption needs to be off */ #define x86_test_and_clear_bit_percpu(bit, var) \ diff --git a/include/asm-generic/percpu.h b/include/asm-generic/percpu.h index 00f45ff..c57357e 100644 --- a/include/asm-generic/percpu.h +++ b/include/asm-generic/percpu.h @@ -120,6 +120,14 @@ do { \ # define percpu_sub(var, val) __percpu_generic_to_op(var, (val), -=) #endif +#ifndef percpu_inc +# define percpu_inc(var) do { percpu_add(var, 1); } while (0) +#endif + +#ifndef percpu_dec +# define percpu_dec(var) do { percpu_sub(var, 1); } while (0) +#endif + #ifndef percpu_and # define percpu_and(var, val) __percpu_generic_to_op(var, (val), &=) #endif -- 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/