The patch titled
Subject: mm/page_alloc: warn on nr_reserved_highatomic underflow
has been added to the -mm mm-unstable branch. Its filename is
mm-page_alloc-warn-on-nr_reserved_highatomic-underflow.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-page_alloc-warn-on-nr_reserved_highatomic-underflow.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: Brendan Jackman <jackmanb@xxxxxxxxxx>
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@xxxxxxxxxxx/T/#m3da87e6cc3348a4640aa298137bc9f8f61b76c84
Link: https://lkml.kernel.org/r/20250225-warn-underflow-v1-1-3dc542941d3a@xxxxxxxxxx
Signed-off-by: Brendan Jackman <jackmanb@xxxxxxxxxx>
Reviewed-by: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
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@xxxxxxxxxx are
mm-mmu_gather-update-comment-on-rcu-freeing.patch
selftests-mm-report-errno-when-things-fail-in-gup_longterm.patch
selftests-mm-fix-assumption-that-sudo-is-present.patch
selftests-mm-skip-uffd-stress-if-userfaultfd-not-available.patch
selftests-mm-skip-uffd-wp-mremap-if-userfaultfd-not-available.patch
selftests-mm-uffd-rename-nr_cpus-nr_threads.patch
selftests-mm-print-some-details-when-uffd-stress-gets-bad-params.patch
selftests-mm-dont-fail-uffd-stress-if-too-many-cpus.patch
selftests-mm-skip-map_populate-on-weird-filesystems.patch
selftests-mm-skip-gup_longerm-tests-on-weird-filesystems.patch
mm-page_alloc-warn-on-nr_reserved_highatomic-underflow.patch
scripts-gdb-add-lx_per_cpu_ptr.patch
