From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx116.postini.com [74.125.245.116]) by kanga.kvack.org (Postfix) with SMTP id EC44F6B002B for ; Fri, 14 Dec 2012 11:13:06 -0500 (EST) Received: by mail-vb0-f41.google.com with SMTP id l22so4361180vbn.14 for ; Fri, 14 Dec 2012 08:13:05 -0800 (PST) MIME-Version: 1.0 In-Reply-To: <20121214144927.GS4939@ZenIV.linux.org.uk> References: <3b624af48f4ba4affd78466b73b6afe0e2f66549.1355463438.git.luto@amacapital.net> <20121214072755.GR4939@ZenIV.linux.org.uk> <20121214144927.GS4939@ZenIV.linux.org.uk> From: Andy Lutomirski Date: Fri, 14 Dec 2012 08:12:45 -0800 Message-ID: Subject: Re: [PATCH] mm: Downgrade mmap_sem before locking or populating on mmap Content-Type: text/plain; charset=ISO-8859-1 Sender: owner-linux-mm@kvack.org List-ID: To: Al Viro Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton , Ingo Molnar , Michel Lespinasse , Hugh Dickins , J??rn Engel On Fri, Dec 14, 2012 at 6:49 AM, Al Viro wrote: > 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? Oh, /that/ call to get_user_pages. That would qualify as screwing up... Since dropping and reacquiring mmap_sem there is probably a bad idea there, I'll rework this and post a v2. --Andy -- 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/ . Don't email: email@kvack.org