From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-la0-f53.google.com (mail-la0-f53.google.com [209.85.215.53]) by kanga.kvack.org (Postfix) with ESMTP id 5ECE96B006C for ; Tue, 3 Feb 2015 14:32:12 -0500 (EST) Received: by mail-la0-f53.google.com with SMTP id gq15so54225361lab.12 for ; Tue, 03 Feb 2015 11:32:11 -0800 (PST) Date: Tue, 3 Feb 2015 11:31:15 -0800 From: Shaohua Li Subject: Re: [PATCH 2/2] aio: make aio .mremap handle size changes Message-ID: <20150203193115.GA296459@devbig257.prn2.facebook.com> References: <798fafb96373cfab0707457a266dd137016cd1e9.1422986358.git.shli@fb.com> <20150203192323.GT2974@kvack.org> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <20150203192323.GT2974@kvack.org> Sender: owner-linux-mm@kvack.org List-ID: To: Benjamin LaHaise Cc: linux-mm@kvack.org, Kernel-team@fb.com, Andrew Morton On Tue, Feb 03, 2015 at 02:23:23PM -0500, Benjamin LaHaise wrote: > On Tue, Feb 03, 2015 at 11:18:53AM -0800, Shaohua Li wrote: > > mremap aio ring buffer to another smaller vma is legal. For example, > > mremap the ring buffer from the begining, though after the mremap, some > > ring buffer pages can't be accessed in userspace because vma size is > > shrinked. The problem is ctx->mmap_size isn't changed if the new ring > > buffer vma size is changed. Latter io_destroy will zap all vmas within > > mmap_size, which might zap unrelated vmas. > > Nak. Shrinking the aio ring buffer is not a supported operation and will > cause the application to lose events. Make the size changing mremap fail, > as this patch will not make the system do the right thing. Yes, making the syscall fail (vma ops has .remap) is another option. If the app uses io_getevents(), looks the app will not lose events, no? On the other hand, I just want to make sure kernel does the right thing (not zap unrelated vmas). If app does crazy things, it will break. Thanks, Shaohua -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org