+ maple_tree-fix-mas_skip_node-end-slot-detection.patch added to mm-hotfixes-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: maple_tree: fix mas_skip_node() end slot detection
has been added to the -mm mm-hotfixes-unstable branch.  Its filename is
     maple_tree-fix-mas_skip_node-end-slot-detection.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/maple_tree-fix-mas_skip_node-end-slot-detection.patch

This patch will later appear in the mm-hotfixes-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: "Liam R. Howlett" <Liam.Howlett@oracle.com>
Subject: maple_tree: fix mas_skip_node() end slot detection
Date: Thu, 2 Mar 2023 21:15:39 -0500

mas_skip_node() is used to move the maple state to the node with a higher
limit.  It does this by walking up the tree and increasing the slot count.
Since slot count may not be able to be increased, it may need to walk up
multiple times to find room to walk right to a higher limit node.  The
limit of slots that was being used was the node limit and not the last
location of data in the node.  This would cause the maple state to be
shifted outside actual data and enter an error state, thus returning
-EBUSY.

The result of the incorrect error state means that mas_awalk() would
return an error instead of finding the allocation space.

The fix is to use mas_data_end() in mas_skip_node() to detect the nodes
data end point and continue walking the tree up until it is safe to move
to a node with a higher limit.

mas_skip_node() may also be passed a maple state in an error state from
mas_anode_descend() when no allocations are available.  Return on such an
error state immediately.

Link: https://lkml.kernel.org/r/20230303021540.1056603-1-Liam.Howlett@oracle.com
Fixes: 54a611b60590 ("Maple Tree: add new data structure")
Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Reported-by: Snild Dolkow <snild@sony.com>
  Link: https://lore.kernel.org/linux-mm/cb8dc31a-fef2-1d09-f133-e9f7b9f9e77a@sony.com/
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---


--- a/lib/maple_tree.c~maple_tree-fix-mas_skip_node-end-slot-detection
+++ a/lib/maple_tree.c
@@ -5099,34 +5099,29 @@ static inline bool mas_rewind_node(struc
  */
 static inline bool mas_skip_node(struct ma_state *mas)
 {
-	unsigned char slot, slot_count;
 	unsigned long *pivots;
 	enum maple_type mt;
 
-	mt = mte_node_type(mas->node);
-	slot_count = mt_slots[mt] - 1;
+	if (mas_is_err(mas))
+		return false;
+
 	do {
 		if (mte_is_root(mas->node)) {
-			slot = mas->offset;
-			if (slot > slot_count) {
+			if (mas->offset >= mas_data_end(mas)) {
 				mas_set_err(mas, -EBUSY);
 				return false;
 			}
 		} else {
 			mas_ascend(mas);
-			slot = mas->offset;
-			mt = mte_node_type(mas->node);
-			slot_count = mt_slots[mt] - 1;
 		}
-	} while (slot > slot_count);
+	} while (mas->offset >= mas_data_end(mas));
 
-	mas->offset = ++slot;
+	mt = mte_node_type(mas->node);
 	pivots = ma_pivots(mas_mn(mas), mt);
-	if (slot > 0)
-		mas->min = pivots[slot - 1] + 1;
-
-	if (slot <= slot_count)
-		mas->max = pivots[slot];
+	mas->min = pivots[mas->offset] + 1;
+	mas->offset++;
+	if (mas->offset < mt_slots[mt])
+		mas->max = pivots[mas->offset];
 
 	return true;
 }
_

Patches currently in -mm which might be from Liam.Howlett@oracle.com are

mm-mprotect-fix-successful-vma_merge-of-next-in-do_mprotect_pkey.patch
maple_tree-fix-mas_skip_node-end-slot-detection.patch
test_maple_tree-add-more-testing-for-mas_empty_area.patch
maple_tree-be-more-cautious-about-dead-nodes.patch
maple_tree-detect-dead-nodes-in-mas_start.patch
maple_tree-fix-freeing-of-nodes-in-rcu-mode.patch
maple_tree-remove-extra-smp_wmb-from-mas_dead_leaves.patch
maple_tree-fix-write-memory-barrier-of-nodes-once-dead-for-rcu-mode.patch
maple_tree-add-smp_rmb-to-dead-node-detection.patch
maple_tree-add-rcu-lock-checking-to-rcu-callback-functions.patch
mm-enable-maple-tree-rcu-mode-by-default.patch