[PATCH] mm: hwpoison: drop lru_add_drain_all() in __soft_offline_page()

[Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>]

A race condition starts to be visible in recent mmotm, where a PG_hwpoison
flag is set on a migration source page *before* it's back in buddy page pool.
This is problematic because no page flag is supposed to be set when freeing
(see __free_one_page().) So the user-visible effect of this race is that it
could trigger the BUG_ON() when soft-offlining is called.

The root cause is that we call lru_add_drain_all() to make sure that the
page is in buddy, but that doesn't work because this function just schedules
a work item and doesn't wait its completion. drain_all_pages() does draining
directly, so simply dropping lru_add_drain_all() solves this problem.

Fixes: commit f15bdfa802bf ("mm/memory-failure.c: fix memory leak in successful soft offlining")
Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: <stable@vger.kernel.org> [3.11+]
---
 mm/memory-failure.c | 2 --
 1 file changed, 2 deletions(-)

diff --git mmotm-2015-02-03-16-38.orig/mm/memory-failure.c mmotm-2015-02-03-16-38/mm/memory-failure.c
index b2a68bde8058..fa44054c205f 100644
--- mmotm-2015-02-03-16-38.orig/mm/memory-failure.c
+++ mmotm-2015-02-03-16-38/mm/memory-failure.c
@@ -1647,8 +1647,6 @@ static int __soft_offline_page(struct page *page, int flags)
 			 * setting PG_hwpoison.
 			 */
 			if (!is_free_buddy_page(page))
-				lru_add_drain_all();
-			if (!is_free_buddy_page(page))
 				drain_all_pages(page_zone(page));
 			SetPageHWPoison(page);
 			if (!is_free_buddy_page(page))
-- 
1.9.3

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