Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755209AbdDRKmY (ORCPT ); Tue, 18 Apr 2017 06:42:24 -0400 Received: from mail-pf0-f193.google.com ([209.85.192.193]:34616 "EHLO mail-pf0-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751392AbdDRKmU (ORCPT ); Tue, 18 Apr 2017 06:42:20 -0400 Date: Tue, 18 Apr 2017 19:42:22 +0900 From: Sergey Senozhatsky To: Christoph Lameter Cc: Sergey Senozhatsky , Minchan Kim , Joonsoo Kim , Andrew Morton , Michal Hocko , Vlastimil Babka , linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@lge.com, Sergey Senozhatsky Subject: Re: copy_page() on a kmalloc-ed page with DEBUG_SLAB enabled (was "zram: do not use copy_page with non-page alinged address") Message-ID: <20170418104222.GB558@jagdpanzerIV.localdomain> References: <20170417014803.GC518@jagdpanzerIV.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.8.1 (2017-04-11) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1478 Lines: 35 On (04/17/17 10:20), Christoph Lameter wrote: > On Mon, 17 Apr 2017, Sergey Senozhatsky wrote: > > Minchan reported that doing copy_page() on a kmalloc(PAGE_SIZE) page > > with DEBUG_SLAB enabled can cause a memory corruption (See below or > > lkml.kernel.org/r/1492042622-12074-2-git-send-email-minchan@kernel.org ) > > Yes the alignment guarantees do not require alignment on a page boundary. > > The alignment for kmalloc allocations is controlled by KMALLOC_MIN_ALIGN. > Usually this is either double word aligned or cache line aligned. > > > that's an interesting problem. arm64 copy_page(), for instance, wants src > > and dst to be page aligned, which is reasonable, while generic copy_page(), > > on the contrary, simply does memcpy(). there are, probably, other callpaths > > that do copy_page() on kmalloc-ed pages and I'm wondering if there is some > > sort of a generic fix to the problem. > > Simple solution is to not allocate pages via the slab allocator but use > the page allocator for this. The page allocator provides proper alignment. sure, but at the same time it's not completely uncommon and unseen thing ~/_next$ git grep kmalloc | grep PAGE_SIZE | wc -l 75 not all, if any, of those pages get into copy_page(), of course. may be... hopefully. so may be a warning would make sense and save time some day. but up to MM people to decide. p.s. Christoph, FYI, gmail automatically marked your message as a spam message, for some reason. -ss