From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755881Ab2LNOtc (ORCPT ); Fri, 14 Dec 2012 09:49:32 -0500 Received: from zeniv.linux.org.uk ([195.92.253.2]:53174 "EHLO ZenIV.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754116Ab2LNOtb (ORCPT ); Fri, 14 Dec 2012 09:49:31 -0500 Date: Fri, 14 Dec 2012 14:49:27 +0000 From: Al Viro To: Andy Lutomirski Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton , Ingo Molnar , Michel Lespinasse , Hugh Dickins , J??rn Engel Subject: Re: [PATCH] mm: Downgrade mmap_sem before locking or populating on mmap Message-ID: <20121214144927.GS4939@ZenIV.linux.org.uk> References: <3b624af48f4ba4affd78466b73b6afe0e2f66549.1355463438.git.luto@amacapital.net> <20121214072755.GR4939@ZenIV.linux.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Dec 14, 2012 at 03:14:50AM -0800, Andy Lutomirski wrote: > > Wait a minute. get_user_pages() relies on ->mmap_sem being held. Unless > > I'm seriously misreading your patch it removes that protection. And yes, > > I'm aware of execve-related exception; it's in special circumstances - > > bprm->mm is guaranteed to be not shared (and we need to rearchitect that > > area anyway, but that's a separate story). > > Unless I completely screwed up the patch, ->mmap_sem is still held for > read (it's downgraded from write). It's just not held for write > anymore. Huh? I'm talking about the call of get_user_pages() in aio_setup_ring(). With your patch it's done completely outside of ->mmap_sem, isn't it?