From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756943AbbCPRER (ORCPT ); Mon, 16 Mar 2015 13:04:17 -0400 Received: from cantor2.suse.de ([195.135.220.15]:55661 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756729AbbCPREP (ORCPT ); Mon, 16 Mar 2015 13:04:15 -0400 Message-ID: <1426525448.28068.121.camel@stgolabs.net> Subject: Re: [PATCH] mm: rcu-protected get_mm_exe_file() From: Davidlohr Bueso To: Konstantin Khlebnikov Cc: Oleg Nesterov , linux-mm@kvack.org, Andrew Morton , linux-kernel@vger.kernel.org, Al Viro Date: Mon, 16 Mar 2015 10:04:08 -0700 In-Reply-To: <5507023B.4090905@yandex-team.ru> References: <20150316131257.32340.36600.stgit@buzz> <20150316140720.GA1859@redhat.com> <1426517419.28068.118.camel@stgolabs.net> <5507023B.4090905@yandex-team.ru> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.12.9 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 2015-03-16 at 19:18 +0300, Konstantin Khlebnikov wrote: > On 16.03.2015 17:50, Davidlohr Bueso wrote: > > On Mon, 2015-03-16 at 15:07 +0100, Oleg Nesterov wrote: > >> 3. and we can remove down_write(mmap_sem) from prctl paths. > >> > >> Actually we can do this even without xchg() above, but we might > >> want to kill MMF_EXE_FILE_CHANGED and test_and_set_bit() check. > > > > Yeah I was waiting for security folks input about this, otherwise this > > still doesn't do it for me as we still have to deal with mmap_sem. > > > > Why? mm->flags are updated atomically. mmap_sem isn't required here. Right, nm I was thinking of the set but Oleg's xchg() idea is obviously correct and a much better approach to mine. The only thing I'd suggest is explicitly commenting the lockless get_mm_exe_file callers, if useful, you can take it from my patch 1.