From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758888AbZEOH4W (ORCPT ); Fri, 15 May 2009 03:56:22 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1756436AbZEOH4I (ORCPT ); Fri, 15 May 2009 03:56:08 -0400 Received: from fg-out-1718.google.com ([72.14.220.154]:58430 "EHLO fg-out-1718.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755651AbZEOH4F (ORCPT ); Fri, 15 May 2009 03:56:05 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=date:message-id:from:to:cc:subject:in-reply-to:references :user-agent:mime-version:content-type; b=vrLvuzMyLkuoYrV9MoIuXUp9lj20Vxic2spgvngZ4LdzGcsj9nq2pgU6DtdFfzmNar cQgB3EsLhkKx6idsBRmcxWft3A5UYp1KnvSHKDtYNrV4Fj03ZuzRyPrf19eaPIb49Xdy f35dnQ1zkColBLLzpT75oKFMnRRFLcYzvoeCk= Date: Fri, 15 May 2009 09:56:03 +0200 Message-ID: <871vqqkdf0.wl%vmayatsk@redhat.com> From: Vitaly Mayatskikh To: Andi Kleen Cc: Vitaly Mayatskikh , Josef Bacik , sandeen@redhat.com, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 2/2] Perform check in iov_iter_fault_in_readable() by check_readable_bytes() In-Reply-To: <87k54iq2gv.fsf@basil.nowhere.org> References: <1242317939-15392-1-git-send-email-v.mayatskih@gmail.com> <1242317939-15392-3-git-send-email-v.mayatskih@gmail.com> <87k54iq2gv.fsf@basil.nowhere.org> User-Agent: Wanderlust/2.15.6 (Almost Unreal) Emacs/22.3 Mule/5.0 (SAKAKI) MIME-Version: 1.0 (generated by SEMI 1.14.6 - "Maruoka") Content-Type: text/plain; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org At Fri, 15 May 2009 08:56:00 +0200, Andi Kleen wrote: > Can you describe how it makes it POSIX friendly? > > My understanding was that EFAULT behaviour was undefined in POSIX. > > The obvious hole in the patch is that all these checks are not race > free -- they don't pin pages -- so if there's a parallel unmap even > with your change they can still fail in the middle. ptr = mmap(0, page_size, ....); ... write(fd, ptr + page_size - 256, 512); Write() will fail here, but it can write first 256 bytes. Previously, all 512 bytes were proceeded, but last 256 bytes were zeroed, and sys_write() returned 256. Not very nice too. -- wbr, Vitaly