From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wi0-f176.google.com (mail-wi0-f176.google.com [209.85.212.176]) by kanga.kvack.org (Postfix) with ESMTP id 435196B0253 for ; Thu, 27 Aug 2015 14:06:11 -0400 (EDT) Received: by wicne3 with SMTP id ne3so82454986wic.0 for ; Thu, 27 Aug 2015 11:06:10 -0700 (PDT) Received: from mail-wi0-f182.google.com (mail-wi0-f182.google.com. [209.85.212.182]) by mx.google.com with ESMTPS id hu1si6454623wib.75.2015.08.27.11.06.09 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 27 Aug 2015 11:06:09 -0700 (PDT) Received: by wicne3 with SMTP id ne3so82454376wic.0 for ; Thu, 27 Aug 2015 11:06:09 -0700 (PDT) Date: Thu, 27 Aug 2015 20:06:07 +0200 From: Michal Hocko Subject: Re: [PATCHv3 4/5] mm: make compound_head() robust Message-ID: <20150827180606.GA29584@dhcp22.suse.cz> References: <55DC550D.5060501@suse.cz> <20150825183354.GC4881@node.dhcp.inet.fi> <20150825201113.GK11078@linux.vnet.ibm.com> <55DCD434.9000704@suse.cz> <20150825211954.GN11078@linux.vnet.ibm.com> <20150826212916.GG11078@linux.vnet.ibm.com> <20150827150917.GF27052@dhcp22.suse.cz> <20150827160355.GI27052@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: Hugh Dickins Cc: "Paul E. McKenney" , Vlastimil Babka , "Kirill A. Shutemov" , Andrew Morton , "Kirill A. Shutemov" , Andrea Arcangeli , Dave Hansen , Johannes Weiner , David Rientjes , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Christoph Lameter On Thu 27-08-15 10:28:48, Hugh Dickins wrote: > On Thu, 27 Aug 2015, Michal Hocko wrote: > > On Thu 27-08-15 17:09:17, Michal Hocko wrote: > > [...] > > > Btw. Do we need the same think for page::mapping and KSM? > > > > I guess we are safe here because the address for mappings comes from > > kmalloc and that aligned properly, right? > > Not quite right, in fact. Because usually the struct address_space > is embedded within the struct inode (at i_data), and the struct inode > embedded within the fs-dependent inode, and that's what's kmalloc'ed. > > What makes the mapping pointer low bits safe is include/linux/fs.h: > struct address_space { > ... > } __attribute__((aligned(sizeof(long)))); Oh, right you are. > Which we first had to add in for the cris architecture, which stumbled > not on a genuine allocated address_space, but on that funny statically > declared swapper_space in mm/swap_state.c. Thanks for the clarification. > But struct anon_vma and KSM's struct stable_node (which depend on > the same scheme for low bits of page->mapping) have no such alignment > attribute specified: those ones are indeed relying on the kmalloc > guarantee as you suppose. > > Does struct rcu_head have no __attribute__((aligned(whatever)))? > Perhaps that attribute should be added when it's needed. That's basically what I meant in the previous email. -- Michal Hocko SUSE Labs -- 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