From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f198.google.com (mail-pf0-f198.google.com [209.85.192.198]) by kanga.kvack.org (Postfix) with ESMTP id 0E4FB6B0003 for ; Mon, 9 Apr 2018 22:33:48 -0400 (EDT) Received: by mail-pf0-f198.google.com with SMTP id p10so6018367pfl.22 for ; Mon, 09 Apr 2018 19:33:48 -0700 (PDT) Received: from mail-sor-f65.google.com (mail-sor-f65.google.com. [209.85.220.65]) by mx.google.com with SMTPS id o88sor463275pfa.90.2018.04.09.19.33.46 for (Google Transport Security); Mon, 09 Apr 2018 19:33:46 -0700 (PDT) Date: Tue, 10 Apr 2018 11:33:39 +0900 From: Minchan Kim Subject: Re: [PATCH] mm: workingset: fix NULL ptr dereference Message-ID: <20180410023339.GB214542@rodete-desktop-imager.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> <7706245c-2661-f28b-f7f9-8f11e1ae932b@huawei.com> <20180409144958.GA211679@rodete-laptop-imager.corp.google.com> <20180409152032.GB11756@bombadil.infradead.org> <20180409230409.GA214542@rodete-desktop-imager.corp.google.com> <20180410011211.GA31282@bombadil.infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180410011211.GA31282@bombadil.infradead.org> Sender: owner-linux-mm@kvack.org List-ID: To: Matthew Wilcox Cc: Chao Yu , Jaegeuk Kim , Christopher Lameter , Andrew Morton , linux-mm , LKML , Johannes Weiner , Jan Kara , Chris Fries , linux-f2fs-devel@lists.sourceforge.net, linux-fsdevel@vger.kernel.org On Mon, Apr 09, 2018 at 06:12:11PM -0700, Matthew Wilcox wrote: > On Tue, Apr 10, 2018 at 08:04:09AM +0900, Minchan Kim wrote: > > On Mon, Apr 09, 2018 at 08:20:32AM -0700, Matthew Wilcox wrote: > > > I don't think this is something the radix tree should know about. > > > > Because shadow entry implementation is hidden by radix tree implemetation. > > IOW, radix tree user cannot know how it works. > > I have no idea what you mean. > > > > SLAB should be checking for it (the patch I posted earlier in this > > > > I don't think it's right approach. SLAB constructor can initialize > > some metadata for slab page populated as well as page zeroing. > > However, __GFP_ZERO means only clearing pages, not metadata. > > So it's different semantic. No need to mix out. > > No, __GFP_ZERO is specified to clear the allocated memory whether > you're allocating from alloc_pages or from slab. What makes no sense > is allocating an object from slab with a constructor *and* __GFP_ZERO. > They're in conflict, and slab can't fulfill both of those requirements. It's a stable material. If you really think it does make sense, please submit patch separately. > > > > thread), but the right place to filter this out is in the caller of > > > radix_tree_maybe_preload -- it's already filtering out HIGHMEM pages, > > > and should filter out GFP_ZERO too. > > > > radix_tree_[maybe]_preload is exported API, which are error-prone > > for out of modules or upcoming customers. > > > > More proper place is __radix_tree_preload. > > I could not disagree with you more. It is the responsibility of the > callers of radix_tree_preload to avoid calling it with nonsense flags > like __GFP_DMA, __GFP_HIGHMEM or __GFP_ZERO. How about this? It would fix current problem and warn potential bugs as well. radix_tree_preload already has done such warning and radix_tree_maybe_preload has skipping for misbehaivor gfp.