Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752008AbaAXRwn (ORCPT ); Fri, 24 Jan 2014 12:52:43 -0500 Received: from smtp.codeaurora.org ([198.145.11.231]:51258 "EHLO smtp.codeaurora.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750997AbaAXRwl (ORCPT ); Fri, 24 Jan 2014 12:52:41 -0500 Message-ID: <52E2A866.1050400@codeaurora.org> Date: Fri, 24 Jan 2014 12:52:38 -0500 From: Christopher Covington User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130106 Thunderbird/17.0.2 MIME-Version: 1.0 To: Will Deacon CC: =?ISO-8859-1?Q?Adrien_Verg=E9?= , Russell King , Catalin Marinas , Ben Dooks , "zhangwei(Jovi)" , Andrew Morton , Randy Dunlap , Mathieu Poirier , Dirk Behme , Michel Dagenais , "linux-arm-kernel@lists.infradead.org" , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH V2 4/6] ARM: Make PID_IN_CONTEXTIDR incompatible with PID_NS References: <1390581656-16372-1-git-send-email-adrienverge@gmail.com> <1390581656-16372-5-git-send-email-adrienverge@gmail.com> <20140124164343.GJ31040@mudshark.cambridge.arm.com> <20140124171754.GM31040@mudshark.cambridge.arm.com> In-Reply-To: <20140124171754.GM31040@mudshark.cambridge.arm.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 01/24/2014 12:17 PM, Will Deacon wrote: > On Fri, Jan 24, 2014 at 05:16:28PM +0000, Adrien Verg? wrote: >> 2014/1/24 Will Deacon : >>> Are you sure about this? The value we write is actually task_pid_nr, which I >>> believe to be globally unique. >> >> You are right: the task_pid_nr is unique in the system. However when >> using namespaces, the so called "PID" is the virtual number that >> processes in different namespaces can share. >> >> This PID is the one visible by user-space tasks, in particular >> user-space tracers and debuggers. These programs would expect to find >> the PID of the traced process in the Context ID reg, while it is not. >> I think it is better to remove confusion by making PID_IN_CONTEXTIDR >> and PID_NS incompatible. >> >> What do you think? > > I think I'd rather have the global ID than disable a potentially useful > feature, especially since this is likely to be consumed by external trace > tools as opposed to user-space tasks. We've discussed before that the ARM architecture doesn't say what should be written to the CONTEXTIDR, so it's up to us to decide. Will has a use case where the global PID is useful. Adrien's patches present a use case where I think the virtual PID would be useful. I've done work in the past where writing the process group ID was useful. Would it be reasonable to make what's written to the CONTEXTIDR run-time configurable? If so, what would be the best interface for configuring it? Thanks, Christopher -- Employee of Qualcomm Innovation Center, Inc. Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted by the Linux Foundation. -- 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/