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