[PATCH] mm: hwpoison: Use compound_head() flags for huge pages

[James Morse <james.morse@arm.com>]

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.

CC: Punit Agrawal <punit.agrawal@arm.com>
Signed-off-by: James Morse <james.morse@arm.com>
---
This is intended as a fix, but I can't find the patch that introduced this
behaviour. (not recent, and there is a lot of history down there!)

This doesn't apply to stable trees before v3.10...
Cc: stable@vger.kernel.org # 3.10.105

 mm/memory-failure.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index 2527dfeddb00..44a6a33af219 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -1184,7 +1184,10 @@ int memory_failure(unsigned long pfn, int trapno, int flags)
 	 * 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
-- 
2.11.0

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