From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 3A8442F24 for ; Wed, 12 Apr 2023 08:54:00 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id B5D6DC433EF; Wed, 12 Apr 2023 08:53:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1681289640; bh=3Bmj5DEqwhk4UzV4MjOOZWK5SBT2HbPo+gS41TZS4ZE=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=m1bJiAgOcErZwmU6xRzXOQ8+ajE5Ma5cnOwcYI2uY8fupMvQS+uAxcZ1OsMrl+QpU AmUrN5zZRji05YZkfY6/eFHgQNw524aBOScKegKBsZrcXEdqWoKyLfpwA6OIpvrJln vklFcM1Rz513Dnfw10lQrhMvRWLFajCMrvBAQtls= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Peng Zhang , "Liam R. Howlett" , Andrew Morton Subject: [PATCH 6.2 155/173] maple_tree: fix a potential concurrency bug in RCU mode Date: Wed, 12 Apr 2023 10:34:41 +0200 Message-Id: <20230412082844.370739322@linuxfoundation.org> X-Mailer: git-send-email 2.40.0 In-Reply-To: <20230412082838.125271466@linuxfoundation.org> References: <20230412082838.125271466@linuxfoundation.org> User-Agent: quilt/0.67 Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit From: Peng Zhang 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 Reviewed-by: Liam R. Howlett Cc: Signed-off-by: Andrew Morton Signed-off-by: Greg Kroah-Hartman --- lib/maple_tree.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) --- a/lib/maple_tree.c +++ b/lib/maple_tree.c @@ -3659,10 +3659,9 @@ 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; }