mm/hwpoison: fix the lack of one reference count against poisoned page

The lack of one reference count against poisoned page for hwpoison_inject
w/o hwpoison_filter enabled result in hwpoison detect -1 users still
referenced the page, however, the number should be 0 except the poison
handler held one after successfully unmap.  This patch fix it by hold one
referenced count against poisoned page for hwpoison_inject w/ and w/o
hwpoison_filter enabled.

Before patch:

[   71.902112] Injecting memory failure at pfn 224706
[   71.902137] MCE 0x224706: dirty LRU page recovery: Failed
[   71.902138] MCE 0x224706: dirty LRU page still referenced by -1 users

After patch:

[   94.710860] Injecting memory failure at pfn 215b68
[   94.710885] MCE 0x215b68: dirty LRU page recovery: Recovered

Reviewed-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Acked-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Wanpeng Li <liwanp@linux.vnet.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/hwpoison-inject.c

@@ -20,8 +20,6 @@ static int hwpoison_inject(void *data, u64 val)
 	if (!capable(CAP_SYS_ADMIN))
 		return -EPERM;
 
-	if (!hwpoison_filter_enable)
-		goto inject;
 	if (!pfn_valid(pfn))
 		return -ENXIO;
 
@@ -33,6 +31,9 @@ static int hwpoison_inject(void *data, u64 val)
 	if (!get_page_unless_zero(hpage))
 		return 0;
 
+	if (!hwpoison_filter_enable)
+		goto inject;
+
 	if (!PageLRU(p) && !PageHuge(p))
 		shake_page(p, 0);
 	/*