mm/page_alloc: fix memory accept before watermarks gets initialized

commit 800f105
Author: Kirill A. Shutemov <[email protected]>
Date:   Mon Mar 10 10:28:55 2025 +0200

    mm/page_alloc: fix memory accept before watermarks gets initialized

    Watermarks are initialized during the postcore initcall.  Until then, all
    watermarks are set to zero.  This causes cond_accept_memory() to
    incorrectly skip memory acceptance because a watermark of 0 is always met.

    This can lead to a premature OOM on boot.

    To ensure progress, accept one MAX_ORDER page if the watermark is zero.

    Link: https://lkml.kernel.org/r/[email protected]
    Fixes: dcdfdd4 ("mm: Add support for unaccepted memory")
    Signed-off-by: Kirill A. Shutemov <[email protected]>
    Tested-by: Farrah Chen <[email protected]>
    Reported-by: Farrah Chen <[email protected]>
    Acked-by: Vlastimil Babka <[email protected]>
    Reviewed-by: Pankaj Gupta <[email protected]>
    Cc: Ashish Kalra <[email protected]>
    Cc: David Hildenbrand <[email protected]>
    Cc: "Edgecombe, Rick P" <[email protected]>
    Cc: Mel Gorman <[email protected]>
    Cc: "Mike Rapoport (IBM)" <[email protected]>
    Cc: Thomas Lendacky <[email protected]>
    Cc: <[email protected]>    [6.5+]
    Signed-off-by: Andrew Morton <[email protected]>

JIRA: https://issues.redhat.com/browse/RHEL-77742
Signed-off-by: Nico Pache <[email protected]>

Author: PacheNico

mm/page_alloc.c

@@ -6956,7 +6956,7 @@ static inline bool has_unaccepted_memory(void)
 
 static bool cond_accept_memory(struct zone *zone, unsigned int order)
 {
-	long to_accept;
+	long to_accept, wmark;
 	bool ret = false;
 
 	if (!has_unaccepted_memory())
@@ -6965,8 +6965,18 @@ static bool cond_accept_memory(struct zone *zone, unsigned int order)
 	if (list_empty(&zone->unaccepted_pages))
 		return false;
 
+	wmark = promo_wmark_pages(zone);
+
+	/*
+	 * Watermarks have not been initialized yet.
+	 *
+	 * Accepting one MAX_ORDER page to ensure progress.
+	 */
+	if (!wmark)
+		return try_to_accept_memory_one(zone);
+
 	/* How much to accept to get to promo watermark? */
-	to_accept = promo_wmark_pages(zone) -
+	to_accept = wmark -
 		    (zone_page_state(zone, NR_FREE_PAGES) -
 		    __zone_watermark_unusable_free(zone, order, 0) -
 		    zone_page_state(zone, NR_UNACCEPTED));