Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754581AbaDKVb3 (ORCPT ); Fri, 11 Apr 2014 17:31:29 -0400 Received: from mail-ie0-f175.google.com ([209.85.223.175]:57532 "EHLO mail-ie0-f175.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751504AbaDKVb1 (ORCPT ); Fri, 11 Apr 2014 17:31:27 -0400 MIME-Version: 1.0 In-Reply-To: <5347F188.10408@cybernetics.com> References: <53470E26.2030306@cybernetics.com> <5347451C.4060106@amacapital.net> <5347F188.10408@cybernetics.com> Date: Fri, 11 Apr 2014 23:31:27 +0200 Message-ID: Subject: Re: [PATCH 2/6] shm: add sealing API From: David Herrmann To: Tony Battersby Cc: Andy Lutomirski , linux-fsdevel , linux-mm , linux-kernel , "dri-devel@lists.freedesktop.org" Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi On Fri, Apr 11, 2014 at 3:43 PM, Tony Battersby wrote: > Exactly. For O_DIRECT, that would be the call to get_user_pages_fast() > from dio_refill_pages() in fs/direct-io.c, which is ultimately called > from blkdev_direct_IO(). If you drop mmap_sem after pinning a page without taking a write-ref, you break i_mmap_writable / VM_DENYWRITE. In memfd I rely on i_mmap_writable to work, same thing is done by exec() (and the old, now disabled, MAP_DENYWRITE). I don't know whether I should care. I mean, everyone pinning pages and writing to it without holding the mmap_sem has to take a write-ref for each page or it breaks i_mmap_writable. So this seems to be a bug in direct-IO, not in anyone relying on it, right? Thanks David -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/