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authorPeng Zhang <zhangpeng.00@bytedance.com>2023-03-14 15:42:03 +0300
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2023-04-13 17:55:36 +0300
commit240bb94f3510e0ced4877a786520ee47743c880d (patch)
treeffb0053c9d163bc5a9eb52bcccb2ec13bc59c825 /lib
parent4f5760757fa2eee2f118934d116569b6255c4e3b (diff)
downloadlinux-240bb94f3510e0ced4877a786520ee47743c880d.tar.xz
maple_tree: fix a potential concurrency bug in RCU mode
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>
Diffstat (limited to 'lib')
-rw-r--r--lib/maple_tree.c3
1 files changed, 1 insertions, 2 deletions
diff --git a/lib/maple_tree.c b/lib/maple_tree.c
index 08e41a993eb6..e0935a593a1a 100644
--- a/lib/maple_tree.c
+++ b/lib/maple_tree.c
@@ -3654,10 +3654,9 @@ static inline int mas_root_expand(struct ma_state *mas, void *entry)
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;
}