The quilt patch titled
Subject: maple_tree: refine mas_store_root() on storing NULL
has been removed from the -mm tree. Its filename was
maple_tree-refine-mas_store_root-on-storing-null.patch
This patch was dropped because it was merged into the mm-stable branch
of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
------------------------------------------------------
From: Wei Yang <richard.weiyang@xxxxxxxxx>
Subject: maple_tree: refine mas_store_root() on storing NULL
Date: Thu, 31 Oct 2024 23:16:26 +0000
Currently, when storing NULL on mas_store_root(), the behavior could be
improved.
Storing NULLs over the entire tree may result in a node being used to
store a single range. Further stores of NULL may cause the node and
tree to be corrupt and cause incorrect behaviour. Fixing the store to
the root null fixes the issue by ensuring that a range of 0 - ULONG_MAX
results in an empty tree.
Users of the tree may experience incorrect values returned if the tree
was expanded to store values, then overwritten by all NULLS, then
continued to store NULLs over the empty area.
For example possible cases are:
* store NULL at any range result a new node
* store NULL at range [m, n] where m > 0 to a single entry tree result
a new node with range [m, n] set to NULL
* store NULL at range [m, n] where m > 0 to an empty tree result
consecutive NULL slot
* it allows for multiple NULL entries by expanding root
to store NULLs to an empty tree
This patch tries to improve in:
* memory efficient by setting to empty tree instead of using a node
* remove the possibility of consecutive NULL slot which will prohibit
extended null in later operation
Link: https://lkml.kernel.org/r/20241031231627.14316-5-richard.weiyang@xxxxxxxxx
Fixes: 54a611b60590 ("Maple Tree: add new data structure")
Signed-off-by: Wei Yang <richard.weiyang@xxxxxxxxx>
Reviewed-by: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx>
Cc: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx>
Cc: Sidhartha Kumar <sidhartha.kumar@xxxxxxxxxx>
Cc: Lorenzo Stoakes <lorenzo.stoakes@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
lib/maple_tree.c | 13 ++++++++++++-
1 file changed, 12 insertions(+), 1 deletion(-)
--- a/lib/maple_tree.c~maple_tree-refine-mas_store_root-on-storing-null
+++ a/lib/maple_tree.c
@@ -3447,9 +3447,20 @@ static inline void mas_root_expand(struc
return;
}
+/*
+ * mas_store_root() - Storing value into root.
+ * @mas: The maple state
+ * @entry: The entry to store.
+ *
+ * There is no root node now and we are storing a value into the root - this
+ * function either assigns the pointer or expands into a node.
+ */
static inline void mas_store_root(struct ma_state *mas, void *entry)
{
- if (likely((mas->last != 0) || (mas->index != 0)))
+ if (!entry) {
+ if (!mas->index)
+ rcu_assign_pointer(mas->tree->ma_root, NULL);
+ } else if (likely((mas->last != 0) || (mas->index != 0)))
mas_root_expand(mas, entry);
else if (((unsigned long) (entry) & 3) == 2)
mas_root_expand(mas, entry);
_
Patches currently in -mm which might be from richard.weiyang@xxxxxxxxx are
