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Message-ID: <20180410023339.GB214542@rodete-desktop-imager.corp.google.com> Date: Tue, 10 Apr 2018 11:33:39 +0900 From: Minchan Kim <minchan@...nel.org> To: Matthew Wilcox <willy@...radead.org> Cc: Chao Yu <yuchao0@...wei.com>, Jaegeuk Kim <jaegeuk@...nel.org>, Christopher Lameter <cl@...ux.com>, Andrew Morton <akpm@...ux-foundation.org>, linux-mm <linux-mm@...ck.org>, LKML <linux-kernel@...r.kernel.org>, Johannes Weiner <hannes@...xchg.org>, Jan Kara <jack@...e.cz>, Chris Fries <cfries@...gle.com>, linux-f2fs-devel@...ts.sourceforge.net, linux-fsdevel@...r.kernel.org Subject: Re: [PATCH] mm: workingset: fix NULL ptr dereference 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. >From 27ecf7a009d3570d1155c528c7f08040ede68ed3 Mon Sep 17 00:00:00 2001 From: Minchan Kim <minchan@...nel.org> Date: Tue, 10 Apr 2018 11:20:11 +0900 Subject: [PATCH v2] mm: workingset: fix NULL ptr dereference It assumes shadow entries of radix tree rely on the init state that node->private_list allocated newly is list_empty state for the working. Currently, it's initailized in SLAB constructor which means node of radix tree would be initialized only when *slub allocates new page*, not *slub alloctes new object*. If some FS or subsystem pass gfp_mask to __GFP_ZERO, that means newly allocated node can have !list_empty(node->private_list) by memset of slab allocator. It ends up calling NULL deference at workingset_update_node by failing list_empty check. This patch fixes it. Fixes: 449dd6984d0e ("mm: keep page cache radix tree nodes in check") Cc: Johannes Weiner <hannes@...xchg.org> Cc: Jan Kara <jack@...e.cz> Cc: Matthew Wilcox <willy@...radead.org> Cc: Jaegeuk Kim <jaegeuk@...nel.org> Cc: Chao Yu <yuchao0@...wei.com> Cc: Christopher Lameter <cl@...ux.com> Cc: linux-fsdevel@...r.kernel.org Reported-by: Chris Fries <cfries@...gle.com> Signed-off-by: Minchan Kim <minchan@...nel.org> --- lib/radix-tree.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-) diff --git a/lib/radix-tree.c b/lib/radix-tree.c index da9e10c827df..9d68f2a7888e 100644 --- a/lib/radix-tree.c +++ b/lib/radix-tree.c @@ -511,6 +511,16 @@ int radix_tree_preload(gfp_t gfp_mask) { /* Warn on non-sensical use... */ WARN_ON_ONCE(!gfpflags_allow_blocking(gfp_mask)); + /* + * New allocate node must have node->private_list as INIT_LIST_HEAD + * state by workingset shadow memory implementation. + * If user pass __GFP_ZERO by mistake, slab allocator will clear + * node->private_list, which makes a BUG. Rather than going Oops, + * just fix and warn about it. + */ + if (WARN_ON(gfp_mask & __GFP_ZERO)) + gfp_mask &= ~GFP_ZERO + return __radix_tree_preload(gfp_mask, RADIX_TREE_PRELOAD_SIZE); } EXPORT_SYMBOL(radix_tree_preload); @@ -522,7 +532,7 @@ EXPORT_SYMBOL(radix_tree_preload); */ int radix_tree_maybe_preload(gfp_t gfp_mask) { - if (gfpflags_allow_blocking(gfp_mask)) + if (gfpflags_allow_blocking(gfp_mask) && !(gfp_mask & __GFP_ZERO)) return __radix_tree_preload(gfp_mask, RADIX_TREE_PRELOAD_SIZE); /* Preloading doesn't help anything with this gfp mask, skip it */ preempt_disable(); -- 2.17.0.484.g0c8726318c-goog
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