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Subject[PATCH 3.16 198/233] mm/memory-failure.c: use compound_head() flags for huge pages
3.16.48-rc1 review patch.  If anyone has any objections, please let me know.

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

From: James Morse <james.morse@arm.com>

commit 7258ae5c5a2ce2f5969e8b18b881be40ab55433d upstream.

memory_failure() chooses a recovery action function based on the page
flags. For huge pages it uses the tail page flags which don't have
anything interesting set, resulting in:

> Memory failure: 0x9be3b4: Unknown page state
> Memory failure: 0x9be3b4: recovery action for unknown page: Failed

Instead, save a copy of the head page's flags if this is a huge page,
this means if there are no relevant flags for this tail page, we use the
head pages flags instead. This results in the me_huge_page() recovery
action being called:

> Memory failure: 0x9b7969: recovery action for huge page: Delayed

For hugepages that have not yet been allocated, this allows the hugepage
to be dequeued.

Fixes: 524fca1e7356 ("HWPOISON: fix misjudgement of page_action() for errors on mlocked pages")
Link: http://lkml.kernel.org/r/20170524130204.21845-1-james.morse@arm.com
Signed-off-by: James Morse <james.morse@arm.com>
Tested-by: Punit Agrawal <punit.agrawal@arm.com>
Acked-by: Punit Agrawal <punit.agrawal@arm.com>
Acked-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
mm/memory-failure.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)

--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -1179,7 +1179,10 @@ int memory_failure(unsigned long pfn, in
* page_remove_rmap() in try_to_unmap_one(). So to determine page status
* correctly, we save a copy of the page flags at this time.
*/
- page_flags = p->flags;
+ if (PageHuge(p))
+ page_flags = hpage->flags;
+ else
+ page_flags = p->flags;

/*
* unpoison always clear PG_hwpoison inside page lock
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