From: "Liam R. Howlett (Google)" <liam@infradead.org>
To: Andrew Morton <akpm@linux-foundation.org>,
Thomas Graf <tgraf@suug.ch>,
Herbert Xu <herbert@gondor.apana.org.au>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
maple-tree@lists.infradead.org, Lorenzo Stoakes <ljs@kernel.org>,
Chris Mason <mason@kernel.org>, Alice Ryhl <aliceryhl@google.com>,
Andrew Ballance <andrewjballance@gmail.com>,
"Liam R. Howlett (Google)" <liam@infradead.org>
Subject: [PATCH 2/4] maple_tree: Test emptying tree while RCU reading
Date: Wed, 28 Oct 2026 11:42:16 -0400 [thread overview]
Message-ID: <20261028154218.1668182-3-liam@infradead.org> (raw)
In-Reply-To: <20261028154218.1668182-1-liam@infradead.org>
Add a test case for the rcu reader being restarted by emptying the tree.
Signed-off-by: Liam R. Howlett (Google) <liam@infradead.org>
---
lib/test_maple_tree.c | 129 ++++++++++++++++++++++++++++++++++++++++++
1 file changed, 129 insertions(+)
diff --git a/lib/test_maple_tree.c b/lib/test_maple_tree.c
index fb40e193a3cb7..894f5893e1be2 100644
--- a/lib/test_maple_tree.c
+++ b/lib/test_maple_tree.c
@@ -3740,6 +3740,134 @@ static noinline void __init check_range64_in_rcu(struct maple_tree *mt)
rcu_barrier();
}
+/*
+ * A reader that restarts after its leaf died may find a tree without nodes:
+ * emptied, or emptied and then given a single entry at 0. Each case starts
+ * from a tree with nodes, built by check_seq(). The stores run while the
+ * reader holds rcu_read_lock, so they use GFP_ATOMIC.
+ */
+static noinline void __init check_restart_no_node(struct maple_tree *mt)
+{
+ void *ptr = xa_mk_value(1234);
+ void *entry;
+ MA_STATE(mas, mt, 0, 0);
+
+ MT_BUG_ON(mt, !mtree_empty(mt));
+ mt_set_non_kernel(99999);
+
+ /* find: the tree is emptied */
+ mt_init_flags(mt, MT_FLAGS_USE_RCU);
+ check_seq(mt, 100, false);
+ rcu_read_lock();
+ mas_set(&mas, 0);
+ entry = mas_find(&mas, ULONG_MAX);
+ MT_BUG_ON(mt, entry != xa_mk_value(0));
+ MT_BUG_ON(mt, mtree_store_range(mt, 0, ULONG_MAX, NULL, GFP_ATOMIC));
+ entry = mas_find(&mas, ULONG_MAX);
+ MT_BUG_ON(mt, entry != NULL);
+ MT_BUG_ON(mt, mas.status != ma_none);
+ MT_BUG_ON(mt, mas.index != 0);
+ MT_BUG_ON(mt, mas.last != ULONG_MAX);
+ entry = mas_find(&mas, ULONG_MAX);
+ MT_BUG_ON(mt, entry != NULL);
+ MT_BUG_ON(mt, mas.status != ma_none);
+ rcu_read_unlock();
+ mtree_destroy(mt);
+ rcu_barrier();
+
+ /* next: the tree is emptied */
+ mt_init_flags(mt, MT_FLAGS_USE_RCU);
+ check_seq(mt, 100, false);
+ rcu_read_lock();
+ mas_set(&mas, 0);
+ entry = mas_find(&mas, ULONG_MAX);
+ MT_BUG_ON(mt, entry != xa_mk_value(0));
+ MT_BUG_ON(mt, mtree_store_range(mt, 0, ULONG_MAX, NULL, GFP_ATOMIC));
+ entry = mas_next(&mas, ULONG_MAX);
+ MT_BUG_ON(mt, entry != NULL);
+ MT_BUG_ON(mt, mas.status != ma_none);
+ MT_BUG_ON(mt, mas.index != 0);
+ MT_BUG_ON(mt, mas.last != ULONG_MAX);
+ rcu_read_unlock();
+ mtree_destroy(mt);
+ rcu_barrier();
+
+ /* find: the tree is emptied, then holds one entry at 0 */
+ mt_init_flags(mt, MT_FLAGS_USE_RCU);
+ check_seq(mt, 100, false);
+ rcu_read_lock();
+ mas_set(&mas, 0);
+ entry = mas_find(&mas, ULONG_MAX);
+ MT_BUG_ON(mt, entry != xa_mk_value(0));
+ MT_BUG_ON(mt, mtree_store_range(mt, 0, ULONG_MAX, NULL, GFP_ATOMIC));
+ MT_BUG_ON(mt, mtree_store(mt, 0, ptr, GFP_ATOMIC));
+ entry = mas_find(&mas, ULONG_MAX);
+ MT_BUG_ON(mt, entry != NULL);
+ MT_BUG_ON(mt, mas.status != ma_none);
+ MT_BUG_ON(mt, mas.index != 1);
+ MT_BUG_ON(mt, mas.last != ULONG_MAX);
+ rcu_read_unlock();
+ mtree_destroy(mt);
+ rcu_barrier();
+
+ /* find_rev: the tree is emptied */
+ mt_init_flags(mt, MT_FLAGS_USE_RCU);
+ check_seq(mt, 100, false);
+ rcu_read_lock();
+ mas_set(&mas, ULONG_MAX);
+ entry = mas_find_rev(&mas, 0);
+ MT_BUG_ON(mt, entry != xa_mk_value(100));
+ MT_BUG_ON(mt, mtree_store_range(mt, 0, ULONG_MAX, NULL, GFP_ATOMIC));
+ entry = mas_find_rev(&mas, 0);
+ MT_BUG_ON(mt, entry != NULL);
+ MT_BUG_ON(mt, mas.status != ma_none);
+ MT_BUG_ON(mt, mas.index != 0);
+ MT_BUG_ON(mt, mas.last != ULONG_MAX);
+ entry = mas_find_rev(&mas, 0);
+ MT_BUG_ON(mt, entry != NULL);
+ MT_BUG_ON(mt, mas.status != ma_none);
+ rcu_read_unlock();
+ mtree_destroy(mt);
+ rcu_barrier();
+
+ /* prev: the tree is emptied, then holds one entry at 0 */
+ mt_init_flags(mt, MT_FLAGS_USE_RCU);
+ check_seq(mt, 100, false);
+ rcu_read_lock();
+ mas_set(&mas, ULONG_MAX);
+ entry = mas_find_rev(&mas, 0);
+ MT_BUG_ON(mt, entry != xa_mk_value(100));
+ MT_BUG_ON(mt, mtree_store_range(mt, 0, ULONG_MAX, NULL, GFP_ATOMIC));
+ MT_BUG_ON(mt, mtree_store(mt, 0, ptr, GFP_ATOMIC));
+ entry = mas_prev(&mas, 0);
+ MT_BUG_ON(mt, entry != ptr);
+ MT_BUG_ON(mt, mas.status != ma_root);
+ MT_BUG_ON(mt, mas.index != 0);
+ MT_BUG_ON(mt, mas.last != 0);
+ rcu_read_unlock();
+ mtree_destroy(mt);
+ rcu_barrier();
+
+ /* find_rev: the entry at 0 is below the minimum */
+ mt_init_flags(mt, MT_FLAGS_USE_RCU);
+ check_seq(mt, 100, false);
+ rcu_read_lock();
+ mas_set(&mas, ULONG_MAX);
+ entry = mas_find_rev(&mas, 1);
+ MT_BUG_ON(mt, entry != xa_mk_value(100));
+ MT_BUG_ON(mt, mtree_store_range(mt, 0, ULONG_MAX, NULL, GFP_ATOMIC));
+ MT_BUG_ON(mt, mtree_store(mt, 0, ptr, GFP_ATOMIC));
+ entry = mas_find_rev(&mas, 1);
+ MT_BUG_ON(mt, entry != NULL);
+ MT_BUG_ON(mt, mas.status != ma_root);
+ MT_BUG_ON(mt, mas.index != 0);
+ MT_BUG_ON(mt, mas.last != 0);
+ rcu_read_unlock();
+ mtree_destroy(mt);
+ rcu_barrier();
+ mt_set_non_kernel(0);
+}
+
static DEFINE_MTREE(tree);
static int __init maple_tree_seed(void)
{
@@ -4031,6 +4159,7 @@ static int __init maple_tree_seed(void)
check_range64_in_rcu(&tree);
+ check_restart_no_node(&tree);
#if defined(BENCH)
skip:
--
2.47.3
next prev parent reply other threads:[~2026-10-28 15:42 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-10-28 15:42 [PATCH 0/4] Lib fixes for 7.3 Liam R. Howlett (Google)
2026-10-28 15:42 ` [PATCH 1/4] maple_tree: Fix rcu reader NULL dereference after the tree is emptied Liam R. Howlett (Google)
2026-10-28 15:42 ` Liam R. Howlett (Google) [this message]
2026-10-28 15:42 ` [PATCH 3/4] maple_tree: Update internal warning and bug_on code Liam R. Howlett (Google)
2026-10-28 17:54 ` Lorenzo Stoakes (ARM)
2026-10-28 18:37 ` Liam R. Howlett (Google)
2026-10-28 15:42 ` [PATCH 4/4] rhashtable: fix vmalloc() deadlock in atomic rehash Liam R. Howlett (Google)
2026-10-29 2:16 ` Herbert Xu
2026-10-29 10:08 ` Uladzislau Rezki
2026-10-29 14:53 ` Liam R. Howlett (Google)
2026-10-29 16:23 ` Michal Hocko
2026-10-29 20:02 ` Matthew Wilcox
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