From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail138.messagelabs.com (mail138.messagelabs.com [216.82.249.35]) by kanga.kvack.org (Postfix) with ESMTP id 8D54B6B0011 for ; Thu, 12 May 2011 06:43:07 -0400 (EDT) Received: by vws4 with SMTP id 4so1515830vws.14 for ; Thu, 12 May 2011 03:43:05 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <1305147776.2883.1.camel@work-vm> 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> Date: Thu, 12 May 2011 18:43:05 +0800 Message-ID: Subject: Re: [PATCH 2/3] printk: Add %ptc to safely print a task's comm From: =?UTF-8?Q?Am=C3=A9rico_Wang?= Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Sender: owner-linux-mm@kvack.org List-ID: To: John Stultz Cc: LKML , Ted Ts'o , KOSAKI Motohiro , David Rientjes , Dave Hansen , Andrew Morton , linux-mm@kvack.org On Thu, May 12, 2011 at 5:02 AM, John Stultz wrote= : > On Wed, 2011-05-11 at 17:33 +0800, Am=C3=A9rico Wang wrote: >> On Wed, May 11, 2011 at 8:23 AM, John Stultz wr= ote: >> > 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); ? -- 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