From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753089AbeDISia (ORCPT ); Mon, 9 Apr 2018 14:38:30 -0400 Received: from mail.kernel.org ([198.145.29.99]:50790 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752556AbeDISi2 (ORCPT ); Mon, 9 Apr 2018 14:38:28 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 519DD21771 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=jaegeuk@kernel.org Date: Mon, 9 Apr 2018 11:38:27 -0700 From: Jaegeuk Kim To: Minchan Kim Cc: Matthew Wilcox , Christopher Lameter , Andrew Morton , linux-mm , LKML , Johannes Weiner , Jan Kara , Chris Fries , Chao Yu , linux-f2fs-devel@lists.sourceforge.net, linux-fsdevel@vger.kernel.org Subject: Re: [PATCH] mm: workingset: fix NULL ptr dereference Message-ID: <20180409183827.GD17558@jaegeuk-macbookpro.roam.corp.google.com> References: <20180409015815.235943-1-minchan@kernel.org> <20180409024925.GA21889@bombadil.infradead.org> <20180409030930.GA214930@rodete-desktop-imager.corp.google.com> <20180409111403.GA31652@bombadil.infradead.org> <20180409112514.GA195937@rodete-laptop-imager.corp.google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180409112514.GA195937@rodete-laptop-imager.corp.google.com> User-Agent: Mutt/1.8.2 (2017-04-18) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 04/09, Minchan Kim wrote: > On Mon, Apr 09, 2018 at 04:14:03AM -0700, Matthew Wilcox wrote: > > On Mon, Apr 09, 2018 at 12:09:30PM +0900, Minchan Kim wrote: > > > On Sun, Apr 08, 2018 at 07:49:25PM -0700, Matthew Wilcox wrote: > > > > On Mon, Apr 09, 2018 at 10:58:15AM +0900, Minchan Kim wrote: > > > > > It assumes shadow entry of radix tree relies on the init state > > > > > that node->private_list allocated should be list_empty state. > > > > > Currently, it's initailized in SLAB constructor which means > > > > > node of radix tree would be initialized only when *slub allocates > > > > > new page*, not *new object*. So, if some FS or subsystem pass > > > > > gfp_mask to __GFP_ZERO, slub allocator will do memset blindly. > > > > > > > > Wait, what? Who's declaring their radix tree with GFP_ZERO flags? > > > > I don't see anyone using INIT_RADIX_TREE or RADIX_TREE or RADIX_TREE_INIT > > > > with GFP_ZERO. > > > > > > Look at fs/f2fs/inode.c > > > mapping_set_gfp_mask(inode->i_mapping, GFP_F2FS_ZERO); > > > > > > __add_to_page_cache_locked > > > radix_tree_maybe_preload > > > > > > add_to_page_cache_lru > > > > > > What's the wrong with setting __GFP_ZERO with mapping->gfp_mask? > > > > Because it's a stupid thing to do. Pages are allocated and then filled > > from disk. Zeroing them before DMAing to them is just a waste of time. > > Every FSes do address_space to read pages from storage? I'm not sure. > > If you're right, we need to insert WARN_ON to catch up __GFP_ZERO > on mapping_set_gfp_mask at the beginning and remove all of those > stupid thins. > > Jaegeuk, why do you need __GFP_ZERO? Could you explain? Comment says "__GFP_ZERO returns a zeroed page on success." The f2fs maintains two inodes to manage some metadata in the page cache, which requires zeroed data when introducing a new structure. It's not a big deal to avoid __GFP_ZERO for whatever performance reasons tho, does it only matters with f2fs? Thanks,