Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752712Ab1EKBUx (ORCPT ); Tue, 10 May 2011 21:20:53 -0400 Received: from mail.perches.com ([173.55.12.10]:1480 "EHLO mail.perches.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750799Ab1EKBUw (ORCPT ); Tue, 10 May 2011 21:20:52 -0400 Subject: Re: [PATCH 2/3] printk: Add %ptc to safely print a task's comm From: Joe Perches To: John Stultz Cc: LKML , "Ted Ts'o" , KOSAKI Motohiro , David Rientjes , Dave Hansen , Andrew Morton , linux-mm@kvack.org In-Reply-To: <1305076246.2939.67.camel@work-vm> References: <1305073386-4810-1-git-send-email-john.stultz@linaro.org> <1305073386-4810-3-git-send-email-john.stultz@linaro.org> <1305075090.19586.189.camel@Joe-Laptop> <1305076246.2939.67.camel@work-vm> Content-Type: text/plain; charset="UTF-8" Date: Tue, 10 May 2011 18:20:50 -0700 Message-ID: <1305076850.19586.196.camel@Joe-Laptop> Mime-Version: 1.0 X-Mailer: Evolution 2.32.2 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1527 Lines: 32 On Tue, 2011-05-10 at 18:10 -0700, John Stultz wrote: > On Tue, 2011-05-10 at 17:51 -0700, Joe Perches wrote: > > On Tue, 2011-05-10 at 17:23 -0700, 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. > > Could misuse of %ptc (not using current) cause system lockup? > It very well could. Although I don't see other %p options tring to > handle invalid pointers. Any suggestions on how to best handle this? The only one I know of is ipv6 which copies a 16 byte buffer in case the pointed to value is unaligned. I suppose %pI6c could be a problem or maybe %pS too, but it hasn't been in practice. The use of %ptc somehow seemed more error prone. > Most users are current, so forcing the more rare > non-current users to copy it to a buffer first and use the normal %s > would not be of much impact. > > Although I'm not sure if there's precedent for a %p value that didn't > take a argument. Thoughts on that? Anyone else have an opinion here? The uses of %ptc must add an argument or else gcc will complain. I suggest you just ignore the argument value and use current. -- 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/