mm: check_new_page_bad() directly returns in __PG_HWPOISON case

Currently we check page->flags twice for "HWPoisoned" case of
check_new_page_bad(), which can cause a race with unpoisoning.

This race unnecessarily taints kernel with "BUG: Bad page state".
check_new_page_bad() is the only caller of bad_page() which is
interested in __PG_HWPOISON, so let's move the hwpoison related code in
bad_page() to it.

Link: http://lkml.kernel.org/r/20160518100949.GA17299@hori1.linux.bs1.fc.nec.co.jp
Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Acked-by: Mel Gorman <mgorman@techsingularity.net>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 383b14b..f8f3bfc 100644 (file)
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -522,12 +522,6 @@ static void bad_page(struct page *page, const char *reason,
        static unsigned long nr_shown;
        static unsigned long nr_unshown;
 
-       /* Don't complain about poisoned pages */
-       if (PageHWPoison(page)) {
-               page_mapcount_reset(page); /* remove PageBuddy */
-               return;
-       }
-
        /*
         * Allow a burst of 60 reports, then keep quiet for that minute;
         * or allow a steady drip of one report per second.
@@ -1654,6 +1648,9 @@ static void check_new_page_bad(struct page *page)
        if (unlikely(page->flags & __PG_HWPOISON)) {
                bad_reason = "HWPoisoned (hardware-corrupted)";
                bad_flags = __PG_HWPOISON;
+               /* Don't complain about hwpoisoned pages */
+               page_mapcount_reset(page); /* remove PageBuddy */
+               return;
        }
        if (unlikely(page->flags & PAGE_FLAGS_CHECK_AT_PREP)) {
                bad_reason = "PAGE_FLAGS_CHECK_AT_PREP flag set";