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author | 2023-03-14 20:42:03 +0800 | |
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committer | 2023-04-05 18:06:25 -0700 | |
commit | c45ea315a602d45569b08b93e9ab30f6a63a38aa (patch) | |
tree | 754b6e03c5a014256b0dddd6c9f8b57e9ffb0e7c /lib/maple_tree.c | |
parent | maple_tree: fix get wrong data_end in mtree_lookup_walk() (diff) | |
download | linux-c45ea315a602d45569b08b93e9ab30f6a63a38aa.tar.gz linux-c45ea315a602d45569b08b93e9ab30f6a63a38aa.tar.bz2 linux-c45ea315a602d45569b08b93e9ab30f6a63a38aa.zip |
maple_tree: fix a potential concurrency bug in RCU mode
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>
Diffstat (limited to 'lib/maple_tree.c')
-rw-r--r-- | lib/maple_tree.c | 3 |
1 files changed, 1 insertions, 2 deletions
diff --git a/lib/maple_tree.c b/lib/maple_tree.c index b8a230f5d94e..db60edb55f2f 100644 --- a/lib/maple_tree.c +++ b/lib/maple_tree.c @@ -3725,10 +3725,9 @@ 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; } |