From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx170.postini.com [74.125.245.170]) by kanga.kvack.org (Postfix) with SMTP id 5407D6B002C for ; Thu, 1 Mar 2012 10:03:19 -0500 (EST) Date: Thu, 1 Mar 2012 09:03:16 -0600 (CST) From: Christoph Lameter Subject: Re: [PATCH -next] slub: set PG_slab on all of slab pages In-Reply-To: <1330587031.1762.46.camel@leonhard> Message-ID: References: <1330505674-31610-1-git-send-email-namhyung.kim@lge.com> <1330587031.1762.46.camel@leonhard> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org List-ID: To: Namhyung Kim Cc: Namhyung Kim , Pekka Enberg , Matt Mackall , linux-mm@kvack.org, linux-kernel@vger.kernel.org On Thu, 1 Mar 2012, Namhyung Kim wrote: > > You cannot free a tail page of a compound higher order page independently. > > You must free the whole compound. > > > > I meant freeing a *slab object* resides in a compound page using buddy > system API (e.g. free_pages). I know it's definitely a programming > error. However there's no safety net to protect and/or warn such a > misbehavior AFAICS - except for head page which has PG_slab set - when > it happened by any chance. ?? One generally passed a struct page pointer to the page allocator. Slab allocator takes pointers to object. The calls that take a pointer to an object must have a page aligned value. > Without it, it might be possible to free part of tail pages silently, > and cause unexpected not-so-funny results some time later. It should be > hard to find out. Ok then fix the page allocator to BUG() on tail pages. That is an issue with the page allocator not the slab allocator. Adding PG_tail to the flags checked on free should do the trick (at least for 64 bit). -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org