Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753459Ab0HTQHq (ORCPT ); Fri, 20 Aug 2010 12:07:46 -0400 Received: from smtp1.linux-foundation.org ([140.211.169.13]:53610 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752766Ab0HTQHm (ORCPT ); Fri, 20 Aug 2010 12:07:42 -0400 MIME-Version: 1.0 In-Reply-To: References: <20100818203143.735033743@clark.site> <1282308887.3170.5439.camel@zakaz.uk.xensource.com> From: Linus Torvalds Date: Fri, 20 Aug 2010 09:07:14 -0700 Message-ID: Subject: Re: [2/3] mm: fix up some user-visible effects of the stack guard page To: Ian Campbell Cc: linux-kernel@vger.kernel.org, stable@kernel.org, stable-review@kernel.org, akpm@linux-foundation.org, alan@lxorguk.ukuu.org.uk, Greg KH 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 Content-Length: 1384 Lines: 32 On Fri, Aug 20, 2010 at 8:54 AM, Linus Torvalds wrote: > On Fri, Aug 20, 2010 at 5:54 AM, Ian Campbell wrote: >> >> Since we have split the original VMA into 3, shouldn't only the bottom >> one still have VM_GROWSDOWN set? (how can the top two grow down with the >> bottom one in the way?) Certainly it seems wrong to enforce a guard page >> on anything but the bottom VMA (which is what appears to be happening). > > Yes, it does seem like we should teach vma splitting to remove > VM_GROWSDOWN on all but the lowest mapping. Actually, thinking some more about it, that may not be a good idea. Why? Simply because we may want to merge the vma's back together if you do munlock. And it won't (and mustn't) merge if the vm_flags differ in VM_GROWSDOWN. So I do think we want to keep VM_GROWSDOWN (and VM_GROWSUP on PA-RISC) even across a vma split. Of course, we could set a flag whether the vma really does have a guard page or not. That said, it does strike me as rather odd to do VM ops on partial stacks. What are you doing, exactly, to hit this? Linus -- 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/