commit f86e4271978bd93db466d6a95dad4b0fdcdb04f6
author Yang Shi <yang.shi@linaro.org> Fri Jun 03 14:55:38 2016 -0700
committer Linus Torvalds <torvalds@linux-foundation.org> Fri Jun 03 15:06:22 2016 -0700
tree 26ef29934495da598a11c3a177d0294a71c5eae8
parent d8bae33dddc03dc652e1d8cfceebf4f753939de7

mm: check the return value of lookup_page_ext for all call sites

Per the discussion with Joonsoo Kim [1], we need check the return value
of lookup_page_ext() for all call sites since it might return NULL in
some cases, although it is unlikely, i.e.  memory hotplug.

Tested with ltp with "page_owner=0".

[1] http://lkml.kernel.org/r/20160519002809.GA10245@js1304-P5Q-DELUXE

[akpm@linux-foundation.org: fix build-breaking typos]
[arnd@arndb.de: fix build problems from lookup_page_ext]
  Link: http://lkml.kernel.org/r/6285269.2CksypHdYp@wuerfel
[akpm@linux-foundation.org: coding-style fixes]
Link: http://lkml.kernel.org/r/1464023768-31025-1-git-send-email-yang.shi@linaro.org
Signed-off-by: Yang Shi <yang.shi@linaro.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/page_poison.c

diff --git a/mm/page_poison.c b/mm/page_poison.c
index 1eae5fa..2e647c6 100644
--- a/mm/page_poison.c
+++ b/mm/page_poison.c
@@ -54,6 +54,9 @@
 	struct page_ext *page_ext;
 
 	page_ext = lookup_page_ext(page);
+	if (unlikely(!page_ext))
+		return;
+
 	__set_bit(PAGE_EXT_DEBUG_POISON, &page_ext->flags);
 }
 
@@ -62,6 +65,9 @@
 	struct page_ext *page_ext;
 
 	page_ext = lookup_page_ext(page);
+	if (unlikely(!page_ext))
+		return;
+
 	__clear_bit(PAGE_EXT_DEBUG_POISON, &page_ext->flags);
 }
 
@@ -70,7 +76,7 @@
 	struct page_ext *page_ext;
 
 	page_ext = lookup_page_ext(page);
-	if (!page_ext)
+	if (unlikely(!page_ext))
 		return false;
 
 	return test_bit(PAGE_EXT_DEBUG_POISON, &page_ext->flags);