The patch titled
Subject: mm-treewide-redefine-max_order-sanely-fix-fix
has been added to the -mm mm-unstable branch. Its filename is
mm-treewide-redefine-max_order-sanely-fix-fix.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-treewide-redefine-max_order-sanely-fix-fix.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: "Kirill A. Shutemov" <kirill@xxxxxxxxxxxxx>
Subject: mm-treewide-redefine-max_order-sanely-fix-fix
Date: Thu, 6 Apr 2023 10:25:29 +0300
On Wed, Apr 05, 2023 at 10:20:26PM -0700, Guenter Roeck wrote:
>
> This patch results in various boot failures (hang) on arm targets
> in linux-next. 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.
Actually, __ffs() is not defined for 0.
Maybe something like this?
Link: https://lkml.kernel.org/r/20230406072529.vupqyrzqnhyozeyh@xxxxxxxxxxxxxxxxx
Signed-off-by: "Kirill A. Shutemov" <kirill@xxxxxxxxxxxxx>
Cc: Mike Rapoport <rppt@xxxxxxxxxx>
Reported-by: Guenter Roeck <linux@xxxxxxxxxxxx>
Link: https://lkml.kernel.org/r/9460377a-38aa-4f39-ad57-fb73725f92db@xxxxxxxxxxxx
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/memblock.c | 6 +++++-
mm/memory_hotplug.c | 8 +++++++-
2 files changed, 12 insertions(+), 2 deletions(-)
--- a/mm/memblock.c~mm-treewide-redefine-max_order-sanely-fix-fix
+++ a/mm/memblock.c
@@ -2043,7 +2043,11 @@ static void __init __free_pages_memory(u
int order;
while (start < end) {
- order = min_t(int, MAX_ORDER, __ffs(start));
+ /* __ffs() behaviour is undefined for 0 */
+ 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 +605,13 @@ 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;
+
+ /* __ffs() behaviour is undefined for 0 */
+ 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
mm-treewide-redefine-max_order-sanely-fix-fix.patch
