From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754783AbbFSSqr (ORCPT ); Fri, 19 Jun 2015 14:46:47 -0400 Received: from mx1.redhat.com ([209.132.183.28]:43572 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752295AbbFSSqk (ORCPT ); Fri, 19 Jun 2015 14:46:40 -0400 From: Jeff Moyer To: Oleg Nesterov Cc: Al Viro , Andrew Morton , Benjamin LaHaise , linux-aio@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v4 1/3] aio_ring_remap: kill the bogus ctx->dead check References: <20150618184016.GA13488@redhat.com> <20150619175506.GA19348@redhat.com> X-PGP-KeyID: 1F78E1B4 X-PGP-CertKey: F6FE 280D 8293 F72C 65FD 5A58 1FF8 A7CA 1F78 E1B4 X-PCLoadLetter: What the f**k does that mean? Date: Fri, 19 Jun 2015 14:46:38 -0400 In-Reply-To: <20150619175506.GA19348@redhat.com> (Oleg Nesterov's message of "Fri, 19 Jun 2015 19:55:06 +0200") Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.3 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Oleg Nesterov writes: > On 06/18, Jeff Moyer wrote: >> >> Oleg Nesterov writes: >> >> > kill_ioctx() sets ctx->dead and removes ctx from ->ioctx_table >> > "atomically" under mm->ioctx_lock, so aio_ring_remap() can never >> > see a dead ctx. >> > >> > And even -EINVAL doesn't look necessary. Yes, if mremap() races >> > with kill_ioctx() vm_munmap(ctx->mmap_base, ctx->mmap_size) can >> > unmap the wrong region. In this case the buggy application should >> > blame itself. And there are other reasons why that vm_munmap() can >> > be wrong. Say, an application can mremap() the part of aio region >> > and then do io_destroy(). We could change aio_ring_remap() to >> > verify vma->that vma_end - vma->vma_start == ctx->mmap_size but >> > this won't help if the application does munmap() instead. >> >> I don't think this paragraph really fits with the patch. It's >> interesting commentary, > > Well, this time I disagree. It would be better to add a comment, but the > changelog can help too to understand the code and potential problems if > it races with kill_ioctx(). > >> but if you feel strongly enough about it, send a >> patch that undoes b2edffdd912b. ;-) > > No, I think that commit makes sense. Just it was wrong and we need to > fix it. And, in particular, its changelog was wrong (at least confusing), > it looks as if there are strong reasons to prevent this race. So the > changelog above can unconfuse the git-log reader. > > > But. I never argue with maintainers about non-technical issues ;) Well, then we can have Ben weigh in. I'm not trying to make a huge deal out of it. Cheers, Jeff -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in Please read the FAQ at http://www.tux.org/lkml/