[PATCH 3.16.y-ckt 110/183] mm: hwpoison: drop lru_add_drain_all() in __soft_offline_page()

[Luis Henriques]

3.16.7-ckt8 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>

commit 9ab3b598d2dfbdb0153ffa7e4b1456bbff59a25d upstream.

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
poo= l.

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
schedule= s a work item and doesn't wait its completion.
drain_all_pages() does drainin= g directly, so simply dropping
lru_add_drain_all() solves this problem.

Fixes: f15bdfa802bf ("mm/memory-failure.c: fix memory leak in successful soft offlining")
Signed-off-by: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
Cc: Andi Kleen <andi@xxxxxxxxxxxxxx>
Cc: Tony Luck <tony.luck@xxxxxxxxx>
Cc: Chen Gong <gong.chen@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Luis Henriques <luis.henriques@xxxxxxxxxxxxx>
---
 mm/memory-failure.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index a013bc94ebbe..607a6d62bcab 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -1649,8 +1649,6 @@ 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();
 			SetPageHWPoison(page);
 			if (!is_free_buddy_page(page))
--
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