The quilt patch titled Subject: maple_tree: fix a potential concurrency bug in RCU mode has been removed from the -mm tree. Its filename was maple_tree-fix-a-potential-concurrency-bug-in-rcu-mode.patch

This patch was dropped because it was merged into the mm-hotfixes-stable branch of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

------------------------------------------------------ From: Peng Zhang zhangpeng.00@bytedance.com Subject: maple_tree: fix a potential concurrency bug in RCU mode Date: Tue, 14 Mar 2023 20:42:03 +0800

There is a concurrency bug that may cause the wrong value to be loaded when a CPU is modifying the maple tree.

CPU1: mtree_insert_range() mas_insert() mas_store_root() ... mas_root_expand() ... rcu_assign_pointer(mas->tree->ma_root, mte_mk_root(mas->node)); ma_set_meta(node, maple_leaf_64, 0, slot); <---IP

CPU2: mtree_load() mtree_lookup_walk() ma_data_end();

When CPU1 is about to execute the instruction pointed to by IP, the ma_data_end() executed by CPU2 may return the wrong end position, which will cause the value loaded by mtree_load() to be wrong.

An example of triggering the bug:

Add mdelay(100) between rcu_assign_pointer() and ma_set_meta() in mas_root_expand().

static DEFINE_MTREE(tree); int work(void *p) { unsigned long val; for (int i = 0 ; i< 30; ++i) { val = (unsigned long)mtree_load(&tree, 8); mdelay(5); pr_info("%lu",val); } return 0; }

mt_init_flags(&tree, MT_FLAGS_USE_RCU); mtree_insert(&tree, 0, (void*)12345, GFP_KERNEL); run_thread(work) mtree_insert(&tree, 1, (void*)56789, GFP_KERNEL);

In RCU mode, mtree_load() should always return the value before or after the data structure is modified, and in this example mtree_load(&tree, 8) may return 56789 which is not expected, it should always return NULL. Fix it by put ma_set_meta() before rcu_assign_pointer().

Link: https://lkml.kernel.org/r/20230314124203.91572-4-zhangpeng.00@bytedance.com Fixes: 54a611b60590 ("Maple Tree: add new data structure") Signed-off-by: Peng Zhang zhangpeng.00@bytedance.com Reviewed-by: Liam R. Howlett Liam.Howlett@oracle.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

lib/maple_tree.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-)

--- a/lib/maple_tree.c~maple_tree-fix-a-potential-concurrency-bug-in-rcu-mode +++ a/lib/maple_tree.c @@ -3725,10 +3725,9 @@ static inline int mas_root_expand(struct slot++; mas->depth = 1; mas_set_height(mas); - + ma_set_meta(node, maple_leaf_64, 0, slot); /* swap the new root into the tree */ rcu_assign_pointer(mas->tree->ma_root, mte_mk_root(mas->node)); - ma_set_meta(node, maple_leaf_64, 0, slot); return slot; }

_

Patches currently in -mm which might be from zhangpeng.00@bytedance.com are

mm-kfence-improve-the-performance-of-__kfence_alloc-and-__kfence_free.patch maple_tree-simplify-mas_wr_node_walk.patch