From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail191.messagelabs.com (mail191.messagelabs.com [216.82.242.19]) by kanga.kvack.org (Postfix) with SMTP id CFD5F6B004A for ; Thu, 11 Nov 2010 06:19:14 -0500 (EST) Message-ID: <4CDBD12C.4010807@kernel.dk> Date: Thu, 11 Nov 2010 12:19:08 +0100 From: Jens Axboe MIME-Version: 1.0 Subject: Re: INFO: suspicious rcu_dereference_check() usage - kernel/pid.c:419 invoked rcu_dereference_check() without protection! References: <20101107182028.GZ15561@linux.vnet.ibm.com> <20101108151509.GA3702@redhat.com> <20101109202900.GV4032@linux.vnet.ibm.com> <20101110155530.GA1905@redhat.com> <20101110160211.GA2562@redhat.com> In-Reply-To: <20101110160211.GA2562@redhat.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org To: Oleg Nesterov Cc: "Paul E. McKenney" , Greg Thelen , linux-kernel@vger.kernel.org, linux-mm@kvack.org List-ID: On 2010-11-10 17:02, Oleg Nesterov wrote: > (another try with the proper email address) > > On 11/09, Paul E. McKenney wrote: >> >> Thank you, Oleg! Greg, would you be willing to update your patch >> to remove the comment? (Perhaps tasklist_lock as well...) > > Agreed, I think tasklock should be killed. > > > But wait. Whatever we do, isn't this code racy? I do not see why, say, > sys_ioprio_set(IOPRIO_WHO_PROCESS) can't install ->io_context after > this task has already passed exit_io_context(). > > Jens, am I missed something? Not sure, I think the original intent was for the tasklist_lock to protect from a concurrent exit, but that looks like nonsense and it was just there to protect the task lookup. How about moving the ->io_context check and exit_io_context() in do_exit() under the task lock? Coupled with a check for PF_EXITING in set_task_ioprio(). -- Jens Axboe -- 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 policy in Canada: sign http://dissolvethecrtc.ca/ Don't email: email@kvack.org