mm: hwpoison: adjust for new thp refcounting

Some mm-related BUG_ON()s could trigger from hwpoison code due to recent
changes in thp refcounting rule.  This patch fixes them up.

In the new refcounting, we no longer use tail->_mapcount to keep tail's
refcount, and thereby we can simplify get/put_hwpoison_page().

And another change is that tail's refcount is not transferred to the raw
page during thp split (more precisely, in new rule we don't take
refcount on tail page any more.) So when we need thp split, we have to
transfer the refcount properly to the 4kB soft-offlined page before
migration.

thp split code goes into core code only when precheck
(total_mapcount(head) == page_count(head) - 1) passes to avoid useless
split, where we assume that one refcount is held by the caller of thp
split and the others are taken via mapping.  To meet this assumption,
this patch moves thp split part in soft_offline_page() after
get_any_page().

[akpm@linux-foundation.org: remove unneeded #define, per Kirill]
Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Acked-by: Kirill A.  Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 1 insertions, 1 deletions

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 6b56cfd9fd09..e4397f640e86 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2217,7 +2217,7 @@ extern int memory_failure(unsigned long pfn, int trapno, int flags);
 extern void memory_failure_queue(unsigned long pfn, int trapno, int flags);
 extern int unpoison_memory(unsigned long pfn);
 extern int get_hwpoison_page(struct page *page);
-extern void put_hwpoison_page(struct page *page);
+#define put_hwpoison_page(page)	put_page(page)
 extern int sysctl_memory_failure_early_kill;
 extern int sysctl_memory_failure_recovery;
 extern void shake_page(struct page *p, int access);