Wendy Wang reported off-list that a RAS HWPOISON-SOFT test case failed
and bisected it to the commit 479f854a207c ("mm, page_alloc: defer
debugging checks of pages allocated from the PCP").

The problem is that a page that was poisoned with madvise() is reused.
The commit removed a check that would trigger if DEBUG_VM was enabled
but re-enabling the check only fixes the problem as a side-effect by
printing a bad_page warning and recovering.

The root of the problem is that an madvise() can leave a poisoned page
on the per-cpu list.  This patch drains all per-cpu lists after pages
are poisoned so that they will not be reused.  Wendy reports that the
test case in question passes with this patch applied.  While this could
be done in a targeted fashion, it is over-complicated for such a rare
operation.

Link: http://lkml.kernel.org/r/20170828133414.7qro57jbepdcyz5x@techsingularity.net
Fixes: 479f854a207c ("mm, page_alloc: defer debugging checks of pages allocated from the PCP")
Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
Reported-by: Wang, Wendy <wendy.wang@intel.com>
Tested-by: Wang, Wendy <wendy.wang@intel.com>
Acked-by: David Rientjes <rientjes@google.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: "Hansen, Dave" <dave.hansen@intel.com>
Cc: "Luck, Tony" <tony.luck@intel.com>
Cc: Naoya Horiguchi <nao.horiguchi@gmail.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>