From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail202.messagelabs.com (mail202.messagelabs.com [216.82.254.227]) by kanga.kvack.org (Postfix) with ESMTP id 07067900001 for ; Thu, 12 May 2011 14:07:11 -0400 (EDT) Received: from d03relay03.boulder.ibm.com (d03relay03.boulder.ibm.com [9.17.195.228]) by e33.co.us.ibm.com (8.14.4/8.13.1) with ESMTP id p4CHsAv6029547 for ; Thu, 12 May 2011 11:54:11 -0600 Received: from d03av02.boulder.ibm.com (d03av02.boulder.ibm.com [9.17.195.168]) by d03relay03.boulder.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id p4CI1ASw018044 for ; Thu, 12 May 2011 12:01:13 -0600 Received: from d03av02.boulder.ibm.com (loopback [127.0.0.1]) by d03av02.boulder.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id p4CC0gDP017384 for ; Thu, 12 May 2011 06:00:42 -0600 Subject: Re: [PATCH 2/3] printk: Add %ptc to safely print a task's comm From: John Stultz In-Reply-To: References: <1305073386-4810-1-git-send-email-john.stultz@linaro.org> <1305073386-4810-3-git-send-email-john.stultz@linaro.org> <1305147776.2883.1.camel@work-vm> Content-Type: text/plain; charset="UTF-8" Date: Thu, 12 May 2011 11:01:05 -0700 Message-ID: <1305223265.2680.20.camel@work-vm> Mime-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: owner-linux-mm@kvack.org List-ID: To: =?ISO-8859-1?Q?Am=E9rico?= Wang Cc: LKML , Ted Ts'o , KOSAKI Motohiro , David Rientjes , Dave Hansen , Andrew Morton , linux-mm@kvack.org On Thu, 2011-05-12 at 18:43 +0800, AmA(C)rico Wang wrote: > On Thu, May 12, 2011 at 5:02 AM, John Stultz wrote: > > On Wed, 2011-05-11 at 17:33 +0800, AmA(C)rico Wang wrote: > >> On Wed, May 11, 2011 at 8:23 AM, John Stultz wrote: > >> > Acessing task->comm requires proper locking. However in the past > >> > access to current->comm could be done without locking. This > >> > is no longer the case, so all comm access needs to be done > >> > while holding the comm_lock. > >> > > >> > In my attempt to clean up unprotected comm access, I've noticed > >> > most comm access is done for printk output. To simpify correct > >> > locking in these cases, I've introduced a new %ptc format, > >> > which will safely print the corresponding task's comm. > >> > > >> > Example use: > >> > printk("%ptc: unaligned epc - sending SIGBUS.\n", current); > >> > > >> > >> Why do you hide current->comm behide printk? > >> How is this better than printk("%s: ....", task_comm(current)) ? > > > > So to properly access current->comm, you need to hold the task-lock (or > > with my new patch set, the comm_lock). Rather then adding locking to all > > the call sites that printk("%s ...", current->comm), I'm suggesting we > > add a new %ptc method which will handle the locking for you. > > > > Sorry, I meant why not adding the locking into a wrapper function, > probably get_task_comm() and let the users to call it directly? > > Why is %ptc better than > > char comm[...]; > get_task_comm(comm, current); > printk("%s: ....", comm); There were concerns about the extra stack usage caused adding a comm buffer to each location, which can be avoided by adding the functionality to printk. Further it reduces the amount of change necessary to correct invalid usage. thanks -john -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org