[merged mm-stable] mm-page_alloc-warn-on-nr_reserved_highatomic-underflow.patch removed from -mm tree

[merged mm-stable] mm-page_alloc-warn-on-nr_reserved_highatomic-underflow.patch removed from -mm tree

[Andrew Morton]

The quilt patch titled
     Subject: mm/page_alloc: warn on nr_reserved_highatomic underflow
has been removed from the -mm tree.  Its filename was
     mm-page_alloc-warn-on-nr_reserved_highatomic-underflow.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: Brendan Jackman <jackmanb@google.com>
Subject: mm/page_alloc: warn on nr_reserved_highatomic underflow
Date: Tue, 25 Feb 2025 18:45:09 +0000

As documented in the comment this underflow should not happen.  The
locking has indeed changed here since the comment was written, see the
migratetype hygiene patches[0].  However, those changes made the locking
_safer_, so the underflow _really_ shouldn't happen now.  So upgrade the
comment to a warning.

[0] https://lore.kernel.org/all/20240320180429.678181-7-hannes@cmpxchg.org/T/#m3da87e6cc3348a4640aa298137bc9f8f61b76c84

Link: https://lkml.kernel.org/r/20250225-warn-underflow-v1-1-3dc542941d3a@google.com
Signed-off-by: Brendan Jackman <jackmanb@google.com>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/page_alloc.c |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

--- a/mm/page_alloc.c~mm-page_alloc-warn-on-nr_reserved_highatomic-underflow
+++ a/mm/page_alloc.c
@@ -3095,6 +3095,7 @@ static bool unreserve_highatomic_pageblo
 			if (!page)
 				continue;
 
+			size = max(pageblock_nr_pages, 1UL << order);
 			/*
 			 * It should never happen but changes to
 			 * locking could inadvertently allow a per-cpu
@@ -3102,8 +3103,8 @@ static bool unreserve_highatomic_pageblo
 			 * while unreserving so be safe and watch for
 			 * underflows.
 			 */
-			size = max(pageblock_nr_pages, 1UL << order);
-			size = min(size, zone->nr_reserved_highatomic);
+			if (WARN_ON_ONCE(size > zone->nr_reserved_highatomic))
+				size = zone->nr_reserved_highatomic;
 			zone->nr_reserved_highatomic -= size;
 
 			/*
_

Patches currently in -mm which might be from jackmanb@google.com are

scripts-gdb-add-lx_per_cpu_ptr.patch