Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932215AbXFGRTU (ORCPT ); Thu, 7 Jun 2007 13:19:20 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754088AbXFGRTM (ORCPT ); Thu, 7 Jun 2007 13:19:12 -0400 Received: from nz-out-0506.google.com ([64.233.162.231]:44517 "EHLO nz-out-0506.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759888AbXFGRTL (ORCPT ); Thu, 7 Jun 2007 13:19:11 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=beta; h=received:message-id:date:from:to:subject:cc:in-reply-to:mime-version:content-type:content-transfer-encoding:content-disposition:references; b=lXFBCbWYIN/ikaixqu+/sHeXk/9P+ZQaKH84pKrV5vIpt+2xUV8XL9xX5+Ww3YSjajeK8azPKGVVWPpvirtCVpkj7HLhqCpKOejWoRLKN/4V6zRrPe8mfUPpN5FDdsxZSkX54ndO27IwLKTpDcY7+dw7wyzI4GpFZh8c95v7ZQs= Message-ID: Date: Thu, 7 Jun 2007 22:48:10 +0530 From: "Satyam Sharma" To: "Heiko Carstens" Subject: Re: [patch] i386/x86_64: smp_call_function locking inconsistency Cc: "Jan Glauber" , "David Miller" , akpm@osdl.org, mingo@elte.hu, ak@suse.de, schwidefsky@de.ibm.com, linux-kernel@vger.kernel.org, "Alan Cox" , "Avi Kivity" In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Content-Disposition: inline References: <20070208203210.GB9798@osiris.ibm.com> <20070208.124328.88477956.davem@davemloft.net> <20070209084221.GA8259@osiris.boeblingen.de.ibm.com> <1171025838.5349.14.camel@localhost.localdomain> <20070607162743.GA9433@osiris.ibm.com> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1894 Lines: 55 > On 6/7/07, Heiko Carstens wrote: > [...] > > Avi Kivity has already a patch which introduces an on_cpu() function which > > looks quite like on_each_cpu(). That way you don't have to open code this > > stuff over and over again: > > > > preempt_disable(); > > if (cpu == smp_processor_id()) > > func(); > > else > > smp_call_function_single(...); > > preempt_enable(); > > > > There are already quite a few of these around. > > Indeed -- this was doubly problematic because the un-safeness > was because of smp_processor_id() as well as the (eventual) > access of cpu_online_map (via smp_call_function() -> > num_online_cpus()) ... thanks for letting me know about this. Oh wait, the on_one_cpu() patch proposes on UP: +static inline int on_one_cpu(int cpu, void (*func)(void *info), void *info, + int retry, int wait) +{ /* this needs a if (cpu == 0) check here, IMO */ + local_irq_disable(); + func(info); + local_irq_enable(); + return 0; /* else WARN and return -EINVAL; */ +} which is broken without the suggested additions, IMHO (this is what got me into this in the first place). There _is_ a difference between on_each_cpu() and the smp_call_function* semantics (as discussed on the other thread -- gargh! my mistake for opening this discussion up on so many threads), and in its current form on_one_cpu() has quite confused semantics, trying to mix the two. I guess on_one_cpu() would be better off simply being just an atomic wrapper over smp_processor_id() and smp_call_function_single() (which is the *real* issue that needs solving in the first place), and do it well. Satyam - 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/