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commitc45ea315a6upstream. 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:54a611b605("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>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.