From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752940AbaAKLff (ORCPT ); Sat, 11 Jan 2014 06:35:35 -0500 Received: from atrey.karlin.mff.cuni.cz ([195.113.26.193]:43414 "EHLO atrey.karlin.mff.cuni.cz" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751254AbaAKLfd (ORCPT ); Sat, 11 Jan 2014 06:35:33 -0500 Date: Sat, 11 Jan 2014 12:35:25 +0100 From: Pavel Machek To: Andrew Morton Cc: Tetsuo Handa , joe@perches.com, keescook@chromium.org, geert@linux-m68k.org, jkosina@suse.cz, viro@zeniv.linux.org.uk, davem@davemloft.net, linux-kernel@vger.kernel.org Subject: Re: [PATCH] lib/vsprintf: add %pT format specifier Message-ID: <20140111113525.GA32025@amd.pavel.ucw.cz> References: <201401092151.FIB00084.SJFOLVOMQHtFOF@I-love.SAKURA.ne.jp> <20140110160430.526efb3ea91783fe8a32fec5@linux-foundation.org> <201401111028.DEG34385.FVHtLOFMQJFSOO@I-love.SAKURA.ne.jp> <20140110175730.102b8250.akpm@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140110175730.102b8250.akpm@linux-foundation.org> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri 2014-01-10 17:57:30, Andrew Morton wrote: > On Sat, 11 Jan 2014 10:28:51 +0900 Tetsuo Handa wrote: > > > Andrew Morton wrote: > > > On Thu, 9 Jan 2014 21:52:00 +0900 Tetsuo Handa wrote: > > > > > > > This patch introduces %pT format specifier for printing task_struct->comm. > > > > Currently %pT does not provide consistency. I'm planning to change to use RCU > > > > in the future. By using RCU, the comm name read from task_struct->comm will be > > > > guaranteed to be consistent. But before modifying set_task_comm() to use RCU, > > > > we need to kill direct ->comm users who do not use get_task_comm(). > > > > > > On reflection... > > > > > > It isn't obvious that this patch is sufficiently beneficial until we > > > have that RCU code in place. > > > > > > So I could retain this patch in -mm until we have that all sorted out. > > > And I'll have to avoid merging %pT users into mainline in the > > > meanwhile! > > > > > > Am I wrong? The patch seems fairly pointless as a standalone thing? > > > > > > > Step 1: (targeted to 3.14-rc1) > > Add "%pT" format specifier and commcpy() wrapper function. > > > > Step 2: (started after step 1 is reflected to other git trees) > > Replace printk("%s", p->comm) with printk("%pT", p). > > Replace strcpy(buf, p->comm) with commcpy(buf, p). > > > > Step 3: (started after step 2 is reflected to other git trees) > > Add rcu_read_lock()/rcu_read_unlock() into commcpy(). > > Modify set_task_comm() etc. to replace ->comm using RCU. > > In the absence of step 3, steps 1 and 2 are rather pointless churn. Dunno. Given how often it appears in the code, it looks to me like step 1 is worthwile cleanup on its own... Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html