From ebc29409c2966bd6a6215b27fc654de7f55ce099 Mon Sep 17 00:00:00 2001 From: Brendan Jackman Date: Tue, 25 Feb 2025 18:45:09 +0000 Subject: mm/page_alloc: warn on nr_reserved_highatomic underflow 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 Reviewed-by: Vlastimil Babka Cc: Johannes Weiner Signed-off-by: Andrew Morton --- mm/page_alloc.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) (limited to 'mm/page_alloc.c') diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 945437d7ac44..3c5624380b6c 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -3095,6 +3095,7 @@ static bool unreserve_highatomic_pageblock(const struct alloc_context *ac, 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_pageblock(const struct alloc_context *ac, * 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; /* -- cgit