From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pl0-f69.google.com (mail-pl0-f69.google.com [209.85.160.69]) by kanga.kvack.org (Postfix) with ESMTP id 474516B0003 for ; Sun, 8 Apr 2018 23:09:38 -0400 (EDT) Received: by mail-pl0-f69.google.com with SMTP id 91-v6so6009375pla.18 for ; Sun, 08 Apr 2018 20:09:38 -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 i20sor3792995pfj.126.2018.04.08.20.09.37 for (Google Transport Security); Sun, 08 Apr 2018 20:09:37 -0700 (PDT) Date: Mon, 9 Apr 2018 12:09:30 +0900 From: Minchan Kim Subject: Re: [PATCH] mm: workingset: fix NULL ptr dereference Message-ID: <20180409030930.GA214930@rodete-desktop-imager.corp.google.com> References: <20180409015815.235943-1-minchan@kernel.org> <20180409024925.GA21889@bombadil.infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180409024925.GA21889@bombadil.infradead.org> Sender: owner-linux-mm@kvack.org List-ID: To: Matthew Wilcox Cc: Christopher Lameter , Andrew Morton , linux-mm , LKML , Johannes Weiner , Jan Kara , Chris Fries 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? > > Although, even if nobody's doing that intentionally, if somebody has > a bitflip with the __GFP_ZERO bit, it's going to propagate widely. > I think something like this might be appropriate: > > diff --git a/mm/slub.c b/mm/slub.c > index 9e1100f9298f..0f55f0a0dcaa 100644 > --- a/mm/slub.c > +++ b/mm/slub.c > @@ -2714,8 +2714,10 @@ static __always_inline void *slab_alloc_node(struct kmem_cache *s, > stat(s, ALLOC_FASTPATH); > } > > - if (unlikely(gfpflags & __GFP_ZERO) && object) > - memset(object, 0, s->object_size); > + if (unlikely(gfpflags & __GFP_ZERO) && object) { > + if (!WARN_ON_ONCE(s->ctor)) > + memset(object, 0, s->object_size); > + } > > slab_post_alloc_hook(s, gfpflags, 1, &object); > > > Something you could try is checking that the list is empty when the node > is inserted into the radix tree. > > diff --git a/lib/radix-tree.c b/lib/radix-tree.c > index 8e00138d593f..580f52d0c072 100644 > --- a/lib/radix-tree.c > +++ b/lib/radix-tree.c > @@ -428,6 +428,7 @@ radix_tree_node_alloc(gfp_t gfp_mask, struct radix_tree_node *parent, > ret->exceptional = exceptional; > ret->parent = parent; > ret->root = root; > + BUG_ON(!list_empty(&ret->private_list)); > } > return ret; > }