* [merged mm-hotfixes-stable] maple_tree-test-emptying-tree-while-rcu-reading.patch removed from -mm tree
@ 2026-11-10 6:45 Andrew Morton
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From: Andrew Morton @ 2026-11-10 6:45 UTC (permalink / raw)
To: mm-commits, mason, ljs, andrewjballance, aliceryhl, liam, akpm
The quilt patch titled
Subject: maple_tree: test emptying tree while RCU reading
has been removed from the -mm tree. Its filename was
maple_tree-test-emptying-tree-while-rcu-reading.patch
This patch was dropped because it was merged into the mm-hotfixes-stable branch
of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
------------------------------------------------------
From: "Liam R. Howlett (Google)" <liam@infradead.org>
Subject: maple_tree: test emptying tree while RCU reading
Date: Mon, 02 Nov 2026 21:07:23 -0500
Add a test case for the rcu reader being restarted by emptying the tree.
A reverse walk from index 0 must not return the new root entry.
Link: https://lore.kernel.org/20261103020724.2614498-3-liam@infradead.org
Signed-off-by: Liam R. Howlett (Google) <liam@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Chris Mason <mason@kernel.org>
Cc: Alice Ryhl <aliceryhl@google.com>
Cc: Andrew Ballance <andrewjballance@gmail.com>
---
lib/test_maple_tree.c | 165 ++++++++++++++++++++++++++++++++++++++++
1 file changed, 165 insertions(+)
--- a/lib/test_maple_tree.c~maple_tree-test-emptying-tree-while-rcu-reading
+++ a/lib/test_maple_tree.c
@@ -3740,6 +3740,170 @@ static noinline void __init check_range6
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();
+
+ /* find_rev: the reader is at 0 when the tree gets 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_rev(&mas, 0);
+ 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_rev(&mas, 0);
+ 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();
+
+ /* find_range_rev: the reader is at 0 when the tree gets 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_range_rev(&mas, 0);
+ 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_range_rev(&mas, 0);
+ 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 +4195,7 @@ static int __init maple_tree_seed(void)
check_range64_in_rcu(&tree);
+ check_restart_no_node(&tree);
#if defined(BENCH)
skip:
_
Patches currently in -mm which might be from liam@infradead.org are
maple_tree-update-internal-warning-and-bug_on-code.patch
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2026-11-10 6:45 [merged mm-hotfixes-stable] maple_tree-test-emptying-tree-while-rcu-reading.patch removed from -mm tree Andrew Morton
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