linux-kernel - [PATCH] mm/page_owner: fix incorrect looping in __set_page_owner

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Date:   Fri, 4 Oct 2019 15:37:55 +0800
From:   Miles Chen <miles.chen@...iatek.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
CC:     <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
        <linux-mediatek@...ts.infradead.org>, <wsd_upstream@...iatek.com>,
        Miles Chen <miles.chen@...iatek.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Michal Hocko <mhocko@...e.com>
Subject: [PATCH] mm/page_owner: fix incorrect looping in __set_page_owner_handle()

In __set_page_owner_handle(), we should loop over page
[0...(1 << order) - 1] and setup their page_owner structures.

Currently, __set_page_owner_handle() update page_ext at the end of
the loop, sets the page_owner of (page + 0) twice and
misses the page_owner of (page + (1 << order) - 1).

Fix it by updating the page_ext at the start of the loop.

In i == 0 case:
for (i = 0; i < (1 << order); i++) {
	page_owner = get_page_owner(page_ext); <- page_ext belongs to page + 0
	...
	page_ext = lookup_page_ext(page + i); <- lookup_page_ext(page + 0)
}

Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Vlastimil Babka <vbabka@...e.cz>
Cc: Michal Hocko <mhocko@...e.com>
Signed-off-by: Miles Chen <miles.chen@...iatek.com>
Fixes: 7e2f2a0cd17c ("mm, page_owner: record page owner for each subpage")
---
 mm/page_owner.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/mm/page_owner.c b/mm/page_owner.c
index dee931184788..110c3e1987f2 100644
--- a/mm/page_owner.c
+++ b/mm/page_owner.c
@@ -178,6 +178,7 @@ static inline void __set_page_owner_handle(struct page *page,
 	int i;
 
 	for (i = 0; i < (1 << order); i++) {
+		page_ext = lookup_page_ext(page + i);
 		page_owner = get_page_owner(page_ext);
 		page_owner->handle = handle;
 		page_owner->order = order;
@@ -185,8 +186,6 @@ static inline void __set_page_owner_handle(struct page *page,
 		page_owner->last_migrate_reason = -1;
 		__set_bit(PAGE_EXT_OWNER, &page_ext->flags);
 		__set_bit(PAGE_EXT_OWNER_ACTIVE, &page_ext->flags);
-
-		page_ext = lookup_page_ext(page + i);
 	}
 }
 
-- 
2.18.0