+ list-add-primitives-for-private-list-manipulations.patch added to mm-nonmm-unstable branch

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

The patch titled
     Subject: list: add primitives for private list manipulations
has been added to the -mm mm-nonmm-unstable branch.  Its filename is
     list-add-primitives-for-private-list-manipulations.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/list-add-primitives-for-private-list-manipulations.patch

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

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------------------------------------------------------
From: Pasha Tatashin <pasha.tatashin@soleen.com>
Subject: list: add primitives for private list manipulations
Date: Wed, 26 Nov 2025 13:57:23 -0500

Patch series "list: add primitives for private list manipulations".

Recently linux introduced the ability to mark structure members as
__private and access them via ACCESS_PRIVATE().  This mechanism ensures
that internal implementation details are only accessible by the owning
subsystem, enforcing better encapsulation.

However, struct list_head is frequently used as an internal linkage
mechanism within these private sections.  The standard macros in
<linux/list.h> (such as list_entry and list_for_each_entry) do not support
ACCESS_PRIVATE() natively.  Consequently, subsystems using private lists
are forced to implement ad-hoc workarounds, verbose casting, or local
iterator macros to avoid compiler warnings and access violations.

This series introduces <linux/list_private.h>, which provides a set of
primitives identical in function to those in <linux/list.h>, but designed
specifically for cases where the embedded struct list_head is a private
member.

The series is structured as follows: Core Implementation: Adds the
list_private.h header with support for entry retrieval and iteration
(forward, reverse, safe, etc.).

Testing: Adds a KUnit test suite to verify that the macros compile
correctly and handle pointer offsets/qualifiers as expected.

Adoption: Updates the liveupdate subsystem to use the new generic API,
replacing its local luo_list_for_each_private implementation.


This patch (of 3):

Linux recently added an ability to add private members to structs (i.e. 
__private) and access them via ACCESS_PRIVATE().  This ensures that those
members are only accessible by the subsystem which owns the struct type,
and not to the object owner.

However, struct list_head often needs to be placed into the private
section to be manipulated privately by the subsystem.

Add macros to support private list manipulations in
<linux/list_private.h>.

Link: https://lkml.kernel.org/r/20251126185725.4164769-1-pasha.tatashin@soleen.com
Link: https://lkml.kernel.org/r/20251126185725.4164769-2-pasha.tatashin@soleen.com
Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
Cc: Alexander Graf <graf@amazon.com>
Cc: David Gow <davidgow@google.com>
Cc: David Matlack <dmatlack@google.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Eric Biggers <ebiggers@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Kees Cook <kees@kernel.org>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Pratyush Yadav <pratyush@kernel.org>
Cc: Tamir Duberstein <tamird@gmail.com>
Cc: Dan Carpenter <dan.carpenter@linaro.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 Documentation/core-api/list.rst |    9 +
 include/linux/list_private.h    |  256 ++++++++++++++++++++++++++++++
 2 files changed, 265 insertions(+)

--- a/Documentation/core-api/list.rst~list-add-primitives-for-private-list-manipulations
+++ a/Documentation/core-api/list.rst
@@ -774,3 +774,12 @@ Full List API
 
 .. kernel-doc:: include/linux/list.h
    :internal:
+
+Private List API
+================
+
+.. kernel-doc:: include/linux/list_private.h
+   :doc: Private List Primitives
+
+.. kernel-doc:: include/linux/list_private.h
+   :internal:
diff --git a/include/linux/list_private.h a/include/linux/list_private.h
new file mode 100644
--- /dev/null
+++ a/include/linux/list_private.h
@@ -0,0 +1,256 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+/*
+ * Copyright (c) 2025, Google LLC.
+ * Pasha Tatashin <pasha.tatashin@soleen.com>
+ */
+#ifndef _LINUX_LIST_PRIVATE_H
+#define _LINUX_LIST_PRIVATE_H
+
+/**
+ * DOC: Private List Primitives
+ *
+ * Provides a set of list primitives identical in function to those in
+ * ``<linux/list.h>``, but designed for cases where the embedded
+ * ``&struct list_head`` is private member.
+ */
+
+#include <linux/compiler.h>
+#include <linux/list.h>
+
+#define __list_private_offset(type, member)					\
+	((size_t)(&ACCESS_PRIVATE(((type *)0), member)))
+
+/**
+ * list_private_entry - get the struct for this entry
+ * @ptr:	the &struct list_head pointer.
+ * @type:	the type of the struct this is embedded in.
+ * @member:	the identifier passed to ACCESS_PRIVATE.
+ */
+#define list_private_entry(ptr, type, member) ({				\
+	const struct list_head *__mptr = (ptr);					\
+	(type *)((char *)__mptr - __list_private_offset(type, member));		\
+})
+
+/**
+ * list_private_first_entry - get the first element from a list
+ * @ptr:	the list head to take the element from.
+ * @type:	the type of the struct this is embedded in.
+ * @member:	the identifier passed to ACCESS_PRIVATE.
+ */
+#define list_private_first_entry(ptr, type, member)				\
+	list_private_entry((ptr)->next, type, member)
+
+/**
+ * list_private_last_entry - get the last element from a list
+ * @ptr:	the list head to take the element from.
+ * @type:	the type of the struct this is embedded in.
+ * @member:	the identifier passed to ACCESS_PRIVATE.
+ */
+#define list_private_last_entry(ptr, type, member)				\
+	list_private_entry((ptr)->prev, type, member)
+
+/**
+ * list_private_next_entry - get the next element in list
+ * @pos:	the type * to cursor
+ * @member:	the name of the list_head within the struct.
+ */
+#define list_private_next_entry(pos, member)					\
+	list_private_entry(ACCESS_PRIVATE(pos, member).next, typeof(*(pos)), member)
+
+/**
+ * list_private_next_entry_circular - get the next element in list
+ * @pos:	the type * to cursor.
+ * @head:	the list head to take the element from.
+ * @member:	the name of the list_head within the struct.
+ *
+ * Wraparound if pos is the last element (return the first element).
+ * Note, that list is expected to be not empty.
+ */
+#define list_private_next_entry_circular(pos, head, member)			\
+	(list_is_last(&ACCESS_PRIVATE(pos, member), head) ?			\
+	list_private_first_entry(head, typeof(*(pos)), member) :		\
+	list_private_next_entry(pos, member))
+
+/**
+ * list_private_prev_entry - get the prev element in list
+ * @pos:	the type * to cursor
+ * @member:	the name of the list_head within the struct.
+ */
+#define list_private_prev_entry(pos, member)					\
+	list_private_entry(ACCESS_PRIVATE(pos, member).prev, typeof(*(pos)), member)
+
+/**
+ * list_prev_entry_circular - get the prev element in list
+ * @pos:	the type * to cursor.
+ * @head:	the list head to take the element from.
+ * @member:	the name of the list_head within the struct.
+ *
+ * Wraparound if pos is the first element (return the last element).
+ * Note, that list is expected to be not empty.
+ */
+#define list_private_prev_entry_circular(pos, head, member)			\
+	(list_is_first(&ACCESS_PRIVATE(pos, member), head) ?			\
+	list_private_last_entry(head, typeof(*(pos)), member) :			\
+	list_private_prev_entry(pos, member))
+
+/**
+ * list_private_entry_is_head - test if the entry points to the head of the list
+ * @pos:	the type * to cursor
+ * @head:	the head for your list.
+ * @member:	the name of the list_head within the struct.
+ */
+#define list_private_entry_is_head(pos, head, member)				\
+	list_is_head(&ACCESS_PRIVATE(pos, member), (head))
+
+/**
+ * list_private_for_each_entry - iterate over list of given type
+ * @pos:	the type * to use as a loop cursor.
+ * @head:	the head for your list.
+ * @member:	the name of the list_head within the struct.
+ */
+#define list_private_for_each_entry(pos, head, member)				\
+	for (pos = list_private_first_entry(head, typeof(*pos), member);	\
+	     !list_private_entry_is_head(pos, head, member);			\
+	     pos = list_private_next_entry(pos, member))
+
+/**
+ * list_private_for_each_entry_reverse - iterate backwards over list of given type.
+ * @pos:	the type * to use as a loop cursor.
+ * @head:	the head for your list.
+ * @member:	the name of the list_head within the struct.
+ */
+#define list_private_for_each_entry_reverse(pos, head, member)			\
+	for (pos = list_private_last_entry(head, typeof(*pos), member);		\
+	     !list_private_entry_is_head(pos, head, member);			\
+	     pos = list_private_prev_entry(pos, member))
+
+/**
+ * list_private_for_each_entry_continue - continue iteration over list of given type
+ * @pos:	the type * to use as a loop cursor.
+ * @head:	the head for your list.
+ * @member:	the name of the list_head within the struct.
+ *
+ * Continue to iterate over list of given type, continuing after
+ * the current position.
+ */
+#define list_private_for_each_entry_continue(pos, head, member)			\
+	for (pos = list_private_next_entry(pos, member);			\
+	     !list_private_entry_is_head(pos, head, member);			\
+	     pos = list_private_next_entry(pos, member))
+
+/**
+ * list_private_for_each_entry_continue_reverse - iterate backwards from the given point
+ * @pos:	the type * to use as a loop cursor.
+ * @head:	the head for your list.
+ * @member:	the name of the list_head within the struct.
+ *
+ * Start to iterate over list of given type backwards, continuing after
+ * the current position.
+ */
+#define list_private_for_each_entry_continue_reverse(pos, head, member)		\
+	for (pos = list_private_prev_entry(pos, member);			\
+	     !list_private_entry_is_head(pos, head, member);			\
+	     pos = list_private_prev_entry(pos, member))
+
+/**
+ * list_private_for_each_entry_from - iterate over list of given type from the current point
+ * @pos:	the type * to use as a loop cursor.
+ * @head:	the head for your list.
+ * @member:	the name of the list_head within the struct.
+ *
+ * Iterate over list of given type, continuing from current position.
+ */
+#define list_private_for_each_entry_from(pos, head, member)			\
+	for (; !list_private_entry_is_head(pos, head, member);			\
+	     pos = list_private_next_entry(pos, member))
+
+/**
+ * list_private_for_each_entry_from_reverse - iterate backwards over list of given type
+ *                                    from the current point
+ * @pos:	the type * to use as a loop cursor.
+ * @head:	the head for your list.
+ * @member:	the name of the list_head within the struct.
+ *
+ * Iterate backwards over list of given type, continuing from current position.
+ */
+#define list_private_for_each_entry_from_reverse(pos, head, member)		\
+	for (; !list_private_entry_is_head(pos, head, member);			\
+	     pos = list_private_prev_entry(pos, member))
+
+/**
+ * list_private_for_each_entry_safe - iterate over list of given type safe against removal of list entry
+ * @pos:	the type * to use as a loop cursor.
+ * @n:		another type * to use as temporary storage
+ * @head:	the head for your list.
+ * @member:	the name of the list_head within the struct.
+ */
+#define list_private_for_each_entry_safe(pos, n, head, member)			\
+	for (pos = list_private_first_entry(head, typeof(*pos), member),	\
+		n = list_private_next_entry(pos, member);			\
+	     !list_private_entry_is_head(pos, head, member);			\
+	     pos = n, n = list_private_next_entry(n, member))
+
+/**
+ * list_private_for_each_entry_safe_continue - continue list iteration safe against removal
+ * @pos:	the type * to use as a loop cursor.
+ * @n:		another type * to use as temporary storage
+ * @head:	the head for your list.
+ * @member:	the name of the list_head within the struct.
+ *
+ * Iterate over list of given type, continuing after current point,
+ * safe against removal of list entry.
+ */
+#define list_private_for_each_entry_safe_continue(pos, n, head, member)		\
+	for (pos = list_private_next_entry(pos, member),			\
+		n = list_private_next_entry(pos, member);			\
+	     !list_private_entry_is_head(pos, head, member);			\
+	     pos = n, n = list_private_next_entry(n, member))
+
+/**
+ * list_private_for_each_entry_safe_from - iterate over list from current point safe against removal
+ * @pos:	the type * to use as a loop cursor.
+ * @n:		another type * to use as temporary storage
+ * @head:	the head for your list.
+ * @member:	the name of the list_head within the struct.
+ *
+ * Iterate over list of given type from current point, safe against
+ * removal of list entry.
+ */
+#define list_private_for_each_entry_safe_from(pos, n, head, member)		\
+	for (n = list_private_next_entry(pos, member);				\
+	     !list_private_entry_is_head(pos, head, member);			\
+	     pos = n, n = list_private_next_entry(n, member))
+
+/**
+ * list_private_for_each_entry_safe_reverse - iterate backwards over list safe against removal
+ * @pos:	the type * to use as a loop cursor.
+ * @n:		another type * to use as temporary storage
+ * @head:	the head for your list.
+ * @member:	the name of the list_head within the struct.
+ *
+ * Iterate backwards over list of given type, safe against removal
+ * of list entry.
+ */
+#define list_private_for_each_entry_safe_reverse(pos, n, head, member)		\
+	for (pos = list_private_last_entry(head, typeof(*pos), member),		\
+		n = list_private_prev_entry(pos, member);			\
+	     !list_private_entry_is_head(pos, head, member);			\
+	     pos = n, n = list_private_prev_entry(n, member))
+
+/**
+ * list_private_safe_reset_next - reset a stale list_for_each_entry_safe loop
+ * @pos:	the loop cursor used in the list_for_each_entry_safe loop
+ * @n:		temporary storage used in list_for_each_entry_safe
+ * @member:	the name of the list_head within the struct.
+ *
+ * list_safe_reset_next is not safe to use in general if the list may be
+ * modified concurrently (eg. the lock is dropped in the loop body). An
+ * exception to this is if the cursor element (pos) is pinned in the list,
+ * and list_safe_reset_next is called after re-taking the lock and before
+ * completing the current iteration of the loop body.
+ */
+#define list_private_safe_reset_next(pos, n, member)				\
+	n = list_private_next_entry(pos, member)
+
+#endif /* _LINUX_LIST_PRIVATE_H */
_

Patches currently in -mm which might be from pasha.tatashin@soleen.com are

liveupdate-luo_flb-introduce-file-lifecycle-bound-global-state.patch
tests-liveupdate-add-in-kernel-liveupdate-test.patch
list-add-primitives-for-private-list-manipulations.patch
list-add-kunit-test-for-private-list-primitives.patch
liveupdate-luo_file-use-private-list.patch