From: Peng Zhang zhangpeng.00@bytedance.com
commit c45ea315a602d45569b08b93e9ab30f6a63a38aa upstream.
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 Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- lib/maple_tree.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-)
--- a/lib/maple_tree.c +++ b/lib/maple_tree.c @@ -3654,10 +3654,9 @@ 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; }