[PATCH 1/2] mm/page_alloc: Always remove pages from temporary list

[Mel Gorman <mgorman@techsingularity.net>]

free_unref_page_list() has neglected to remove pages properly from the list
of pages to free since forever. It works by coincidence because list_add
happened to do the right thing adding the pages to just the PCP lists.
However, a later patch added pages to either the PCP list or the zone list
but only properly deleted the page from the list in one path leading to
list corruption and a subsequent failure. As a preparation patch, always
delete the pages from one list properly before adding to another.  On its
own, this fixes nothing although it adds a fractional amount of overhead
but is critical to the next patch.

Reported-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
---
 mm/page_alloc.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 218b28ee49ed..1ec54173b8d4 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3546,6 +3546,8 @@ void free_unref_page_list(struct list_head *list)
 	list_for_each_entry_safe(page, next, list, lru) {
 		struct zone *zone = page_zone(page);
 
+		list_del(&page->lru);
+
 		/* Different zone, different pcp lock. */
 		if (zone != locked_zone) {
 			if (pcp)
-- 
2.35.3