On Mon, Apr 09, 2018 at 07:41:52PM -0700, Matthew Wilcox wrote:
> On Tue, Apr 10, 2018 at 11:33:39AM +0900, Minchan Kim wrote:
> > @@ -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();
>
> No, you've completely misunderstood what's going on in this function.
Okay, I hope this version clear current concerns.
>From fb37c41b90f7d3ead1798e5cb7baef76709afd94 Mon Sep 17 00:00:00 2001
From: Minchan Kim <minchan@xxxxxxxxxx>
Date: Tue, 10 Apr 2018 11:54:57 +0900
Subject: [PATCH v3] 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@xxxxxxxxxxx>
Cc: Jan Kara <jack@xxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Jaegeuk Kim <jaegeuk@xxxxxxxxxx>
Cc: Chao Yu <yuchao0@xxxxxxxxxx>
Cc: Christopher Lameter <cl@xxxxxxxxx>
Cc: linux-fsdevel@xxxxxxxxxxxxxxx
Cc: stable@xxxxxxxxxxxxxxx
Reported-by: Chris Fries <cfries@xxxxxxxxxx>
Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
---
lib/radix-tree.c | 9 +++++++++
mm/filemap.c | 5 +++--
2 files changed, 12 insertions(+), 2 deletions(-)
diff --git a/lib/radix-tree.c b/lib/radix-tree.c
index da9e10c827df..7569e637dbaa 100644
--- a/lib/radix-tree.c
+++ b/lib/radix-tree.c
@@ -470,6 +470,15 @@ static __must_check int __radix_tree_preload(gfp_t gfp_mask, unsigned nr)
struct radix_tree_node *node;
int ret = -ENOMEM;
+ /*
+ * 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;
/*
* Nodes preloaded by one cgroup can be be used by another cgroup, so
* they should never be accounted to any particular memory cgroup.
diff --git a/mm/filemap.c b/mm/filemap.c
index ab77e19ab09c..b6de9d691c8a 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -786,7 +786,7 @@ int replace_page_cache_page(struct page *old, struct page *new, gfp_t gfp_mask)
VM_BUG_ON_PAGE(!PageLocked(new), new);
VM_BUG_ON_PAGE(new->mapping, new);
- error = radix_tree_preload(gfp_mask & ~__GFP_HIGHMEM);
+ error = radix_tree_preload(gfp_mask & ~(__GFP_HIGHMEM | __GFP_ZERO));
if (!error) {
struct address_space *mapping = old->mapping;
void (*freepage)(struct page *);
@@ -842,7 +842,8 @@ static int __add_to_page_cache_locked(struct page *page,
return error;
}
- error = radix_tree_maybe_preload(gfp_mask & ~__GFP_HIGHMEM);
+ error = radix_tree_maybe_preload(gfp_mask &
+ ~(__GFP_HIGHMEM | __GFP_ZERO));
if (error) {
if (!huge)
mem_cgroup_cancel_charge(page, memcg, false);
--
2.17.0.484.g0c8726318c-goog
