mm: hwpoison: drop lru_add_drain_all() in __soft_offline_page()

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@ah.jp.nec.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Chen Gong <gong.chen@linux.intel.com>
Cc: <stable@vger.kernel.org>	[3.11+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index 1a735fad2a13120cd9543b926140af6724858e42..d487f8dc6d392ab7663c2e63317f12e29e37e743 100644 (file)
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -1646,8 +1646,6 @@ static int __soft_offline_page(struct page *page, int flags)
                         * source page should be freed back to buddy before
                         * 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);