[merged mm-stable] mm-treewide-redefine-max_order-sanely-fix-fix.patch removed from -mm tree

[merged mm-stable] mm-treewide-redefine-max_order-sanely-fix-fix.patch removed from -mm tree

[Andrew Morton]

The quilt patch titled
     Subject: mm: avoid passing 0 to __ffs()
has been removed from the -mm tree.  Its filename was
     mm-treewide-redefine-max_order-sanely-fix-fix.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: "Kirill A. Shutemov" <kirill@shutemov.name>
Subject: mm: avoid passing 0 to __ffs()
Date: Thu, 6 Apr 2023 10:25:29 +0300

23baf831a32c ("mm, treewide: redefine MAX_ORDER sanely") results in
various boot failures (hang) on arm targets Debug messages reveal the
reason.

########### MAX_ORDER=10 start=0 __ffs(start)=-1 min()=10 min_t=-1
                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

If start==0, __ffs(start) returns 0xfffffff or (as int) -1, which min_t()
interprets as such, while min() apparently uses the returned unsigned long
value. Obviously a negative order isn't received well by the rest of the
code.

[akpm@linux-foundation.org: fix comment, per Mike]
  Link: https://lkml.kernel.org/r/ZDBa7HWZK69dKKzH@kernel.org
Link: https://lkml.kernel.org/r/20230406072529.vupqyrzqnhyozeyh@box.shutemov.name
Fixes: 23baf831a32c ("mm, treewide: redefine MAX_ORDER sanely")
Signed-off-by: "Kirill A. Shutemov" <kirill@shutemov.name>
Reported-by: Guenter Roeck <linux@roeck-us.net>
  Link: https://lkml.kernel.org/r/9460377a-38aa-4f39-ad57-fb73725f92db@roeck-us.net
Reviewed-by: Mike Rapoport (IBM) <rppt@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/memblock.c       |   11 ++++++++++-
 mm/memory_hotplug.c |   13 ++++++++++++-
 2 files changed, 22 insertions(+), 2 deletions(-)

--- a/mm/memblock.c~mm-treewide-redefine-max_order-sanely-fix-fix
+++ a/mm/memblock.c
@@ -2043,7 +2043,16 @@ static void __init __free_pages_memory(u
 	int order;
 
 	while (start < end) {
-		order = min_t(int, MAX_ORDER, __ffs(start));
+		/*
+		 * Free the pages in the largest chunks alignment allows.
+		 *
+		 * __ffs() behaviour is undefined for 0. start == 0 is
+		 * MAX_ORDER-aligned, set order to MAX_ORDER for the case.
+		 */
+		if (start)
+			order = min_t(int, MAX_ORDER, __ffs(start));
+		else
+			order = MAX_ORDER;
 
 		while (start + (1UL << order) > end)
 			order--;
--- a/mm/memory_hotplug.c~mm-treewide-redefine-max_order-sanely-fix-fix
+++ a/mm/memory_hotplug.c
@@ -605,7 +605,18 @@ static void online_pages_range(unsigned
 	 * this and the first chunk to online will be pageblock_nr_pages.
 	 */
 	for (pfn = start_pfn; pfn < end_pfn;) {
-		int order = min_t(int, MAX_ORDER, __ffs(pfn));
+		int order;
+
+		/*
+		 * Free to online pages in the largest chunks alignment allows.
+		 *
+		 * __ffs() behaviour is undefined for 0. start == 0 is
+		 * MAX_ORDER-aligned, Set order to MAX_ORDER for the case.
+		 */
+		if (pfn)
+			order = min_t(int, MAX_ORDER, __ffs(pfn));
+		else
+			order = MAX_ORDER;
 
 		(*online_page_callback)(pfn_to_page(pfn), order);
 		pfn += (1UL << order);
_

Patches currently in -mm which might be from kirill@shutemov.name are