From mboxrd@z Thu Jan 1 00:00:00 1970 From: Vitaly Mayatskikh Subject: Re: [PATCH 2/2] Perform check in iov_iter_fault_in_readable() by check_readable_bytes() Date: Fri, 15 May 2009 09:56:03 +0200 Message-ID: <871vqqkdf0.wl%vmayatsk@redhat.com> 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> Mime-Version: 1.0 (generated by SEMI 1.14.6 - "Maruoka") Content-Type: text/plain; charset=US-ASCII Cc: Vitaly Mayatskikh , Josef Bacik , sandeen@redhat.com, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org To: Andi Kleen Return-path: 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 In-Reply-To: <87k54iq2gv.fsf@basil.nowhere.org> Sender: linux-fsdevel-owner@vger.kernel.org List-ID: 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