The patch titled
Subject: mm/contig_alloc: fix alloc_contig_range when __GFP_COMP and order < MAX_ORDER
has been added to the -mm mm-hotfixes-unstable branch. Its filename is
mm-contig_alloc-fix-alloc_contig_range-when-__gfp_comp-and-order-max_order.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-contig_alloc-fix-alloc_contig_range-when-__gfp_comp-and-order-max_order.patch
This patch will later appear in the mm-hotfixes-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Jinjiang Tu <tujinjiang@xxxxxxxxxx>
Subject: mm/contig_alloc: fix alloc_contig_range when __GFP_COMP and order < MAX_ORDER
Date: Wed, 12 Mar 2025 16:47:05 +0800
When calling alloc_contig_range() with __GFP_COMP and the order of
requested pfn range is pageblock_order, less than MAX_ORDER, I triggered
WARNING as follows:
PFN range: requested [2150105088, 2150105600), allocated [2150105088, 2150106112)
WARNING: CPU: 3 PID: 580 at mm/page_alloc.c:6877 alloc_contig_range+0x280/0x340
alloc_contig_range() marks pageblocks of the requested pfn range to be
isolated, migrate these pages if they are in use and will be freed to
MIGRATE_ISOLATED freelist.
Suppose two alloc_contig_range() calls at the same time and the requested
pfn range are [0x80280000, 0x80280200) and [0x80280200, 0x80280400)
respectively. Suppose the two memory range are in use, then
alloc_contig_range() will migrate and free these pages to MIGRATE_ISOLATED
freelist. __free_one_page() will merge MIGRATE_ISOLATE buddy to larger
buddy, resulting in a MAX_ORDER buddy. Finally, find_large_buddy() in
alloc_contig_range() returns a MAX_ORDER buddy and results in WARNING.
To fix it, call free_contig_range() to free the excess pfn range.
Link: https://lkml.kernel.org/r/20250312084705.2938220-1-tujinjiang@xxxxxxxxxx
Fixes: e98337d11bbd ("mm/contig_alloc: support __GFP_COMP")
Signed-off-by: Jinjiang Tu <tujinjiang@xxxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: Kefeng Wang <wangkefeng.wang@xxxxxxxxxx>
Cc: Nanyong Sun <sunnanyong@xxxxxxxxxx>
Cc: Yu Zhao <yuzhao@xxxxxxxxxx>
Cc: Zi Yan <ziy@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/page_alloc.c | 13 +++++++++++--
1 file changed, 11 insertions(+), 2 deletions(-)
--- a/mm/page_alloc.c~mm-contig_alloc-fix-alloc_contig_range-when-__gfp_comp-and-order-max_order
+++ a/mm/page_alloc.c
@@ -6528,7 +6528,8 @@ int alloc_contig_range_noprof(unsigned l
goto done;
}
- if (!(gfp_mask & __GFP_COMP)) {
+ if (!(gfp_mask & __GFP_COMP) ||
+ (is_power_of_2(end - start) && ilog2(end - start) < MAX_PAGE_ORDER)) {
split_free_pages(cc.freepages, gfp_mask);
/* Free head and tail (if any) */
@@ -6536,7 +6537,15 @@ int alloc_contig_range_noprof(unsigned l
free_contig_range(outer_start, start - outer_start);
if (end != outer_end)
free_contig_range(end, outer_end - end);
- } else if (start == outer_start && end == outer_end && is_power_of_2(end - start)) {
+
+ outer_start = start;
+ outer_end = end;
+
+ if (!(gfp_mask & __GFP_COMP))
+ goto done;
+ }
+
+ if (start == outer_start && end == outer_end && is_power_of_2(end - start)) {
struct page *head = pfn_to_page(start);
int order = ilog2(end - start);
_
Patches currently in -mm which might be from tujinjiang@xxxxxxxxxx are
mm-hugetlb-fix-surplus-pages-in-dissolve_free_huge_page.patch
mm-contig_alloc-fix-alloc_contig_range-when-__gfp_comp-and-order-max_order.patch
mm-hugetlb-fix-set_max_huge_pages-when-there-are-surplus-pages.patch
