From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754345AbbCXTEj (ORCPT ); Tue, 24 Mar 2015 15:04:39 -0400 Received: from mx1.redhat.com ([209.132.183.28]:54464 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753430AbbCXTEg (ORCPT ); Tue, 24 Mar 2015 15:04:36 -0400 Date: Tue, 24 Mar 2015 20:02:29 +0100 From: Oleg Nesterov To: Konstantin Khlebnikov Cc: Konstantin Khlebnikov , Davidlohr Bueso , "linux-mm@kvack.org" , Andrew Morton , Linux Kernel Mailing List Subject: Re: [PATCH] mm: fix lockdep build in rcu-protected get_mm_exe_file() Message-ID: <20150324190229.GC11834@redhat.com> References: <20150320144715.24899.24547.stgit@buzz> <1427134273.2412.12.camel@stgolabs.net> <20150323191055.GA10212@redhat.com> <55119B3B.5020403@yandex-team.ru> <20150324181016.GA9678@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 03/24, Konstantin Khlebnikov wrote: > > On Tue, Mar 24, 2015 at 9:10 PM, Oleg Nesterov wrote: > >>> > >>> "atomic_read(&mm->mm_users) <= 1" looks a bit more "safe". But again, > >>> I won't insist. > >> > >> Not so safe: this will race with get_task_mm(). > > > > How? > > I mean rcu/lockdep debug migh race with get_task_mm() and generate > false-positive warning about non-protected rcu_dereference. Still can't understand, I think it can't... and if it could, then this warning would not be false positive. Anut this doesn't matter because we seem to agree this check should go away. > > Yeees, probably rcu_dereference_raw() would be even better. set_mm_exe_file() > > must be called only if nobody but us can access this mm. > > Yep. Great. Davidlohr will you agree? Oleg.