mm: memory-failure: fix potential page refcnt leak in memory_failure()

put_ref_page() is not called to drop extra refcnt when comes from madvise
in the case pfn is valid but pgmap is NULL leading to page refcnt leak.

Link: https://lkml.kernel.org/r/20230701072837.1994253-1-linmiaohe@huawei.com
Fixes: 1e8aaedb ("mm,memory_failure: always pin the page in madvise_inject_error")
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Acked-by: Naoya Horiguchi <naoya.horiguchi@nec.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/memory-failure.c

@@ -2117,8 +2117,6 @@ static int memory_failure_dev_pagemap(unsigned long pfn, int flags,
 {
 	int rc = -ENXIO;
 
-	put_ref_page(pfn, flags);
-
 	/* device metadata space is not recoverable */
 	if (!pgmap_pfn_valid(pgmap, pfn))
 		goto out;
@@ -2193,6 +2191,7 @@ int memory_failure(unsigned long pfn, int flags)
 
 		if (pfn_valid(pfn)) {
 			pgmap = get_dev_pagemap(pfn, NULL);
+			put_ref_page(pfn, flags);
 			if (pgmap) {
 				res = memory_failure_dev_pagemap(pfn, flags,
 								 pgmap);