6.6-stable review patch. If anyone has any objections, please let me know.
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From: Wei Yang richard.weiyang@gmail.com
commit 0ea120b278ad7f7cfeeb606e150ad04b192df60b upstream.
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@gmail.com Fixes: 54a611b60590 ("Maple Tree: add new data structure") Signed-off-by: Wei Yang richard.weiyang@gmail.com Reviewed-by: Liam R. Howlett Liam.Howlett@Oracle.com Cc: Liam R. Howlett Liam.Howlett@Oracle.com Cc: Sidhartha Kumar sidhartha.kumar@oracle.com Cc: Lorenzo Stoakes lorenzo.stoakes@oracle.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- lib/maple_tree.c | 13 ++++++++++++- 1 file changed, 12 insertions(+), 1 deletion(-)
--- a/lib/maple_tree.c +++ b/lib/maple_tree.c @@ -3547,9 +3547,20 @@ static inline int mas_root_expand(struct return slot; }
+/* + * 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);