From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Date: Thu, 15 Mar 2018 18:07:47 +0300
Subject: [PATCH] mm/thp: Do not wait for lock_page() in deferred_split_scan()
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deferred_split_scan() gets called from reclaim path. Waiting for page
lock may lead to deadlock there.

Replace lock_page() with trylock_page() and skip the page if we failed
to lock it. We will get to the page on the next scan.

Fixes: 9a982250f773 ("thp: introduce deferred_split_huge_page()")

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Acked-by: Michal Hocko <mhocko@suse.com>
(cherry-picked from https://patchwork.kernel.org/patch/10284703/)
Signed-off-by: Fabian Grünbichler <f.gruenbichler@proxmox.com>
---
 mm/huge_memory.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 0e7ded98d114..4ed6c89e95c3 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2791,11 +2791,13 @@ static unsigned long deferred_split_scan(struct shrinker *shrink,
 
 	list_for_each_safe(pos, next, &list) {
 		page = list_entry((void *)pos, struct page, mapping);
-		lock_page(page);
+		if (!trylock_page(page))
+			goto next;
 		/* split_huge_page() removes page from list on success */
 		if (!split_huge_page(page))
 			split++;
 		unlock_page(page);
+next:
 		put_page(page);
 	}
 
-- 
2.14.2

