mm: memory-failure: fix potential unexpected return value from unpois…

…on_memory()

commit f29623e upstream.

If unpoison_memory() fails to clear page hwpoisoned flag, return value ret
is expected to be -EBUSY.  But when get_hwpoison_page() returns 1 and
fails to clear page hwpoisoned flag due to races, return value will be
unexpected 1 leading to users being confused.  And there's a code smell
that the variable "ret" is used not only to save the return value of
unpoison_memory(), but also the return value from get_hwpoison_page().
Make a further cleanup by using another auto-variable solely to save the
return value of get_hwpoison_page() as suggested by Naoya.

Link: https://lkml.kernel.org/r/20230727115643.639741-3-linmiaohe@huawei.com
Fixes: bf181c5 ("mm/hwpoison: fix unpoison_memory()")
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Naoya Horiguchi <naoya.horiguchi@nec.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

mm/memory-failure.c

@@ -2469,7 +2469,7 @@ int unpoison_memory(unsigned long pfn)
 {
 	struct folio *folio;
 	struct page *p;
-	int ret = -EBUSY;
+	int ret = -EBUSY, ghp;
 	unsigned long count = 1;
 	bool huge = false;
 	static DEFINE_RATELIMIT_STATE(unpoison_rs, DEFAULT_RATELIMIT_INTERVAL,
@@ -2517,29 +2517,28 @@ int unpoison_memory(unsigned long pfn)
 	if (folio_test_slab(folio) || PageTable(&folio->page) || folio_test_reserved(folio))
 		goto unlock_mutex;
 
-	ret = get_hwpoison_page(p, MF_UNPOISON);
-	if (!ret) {
+	ghp = get_hwpoison_page(p, MF_UNPOISON);
+	if (!ghp) {
 		if (PageHuge(p)) {
 			huge = true;
 			count = folio_free_raw_hwp(folio, false);
-			if (count == 0) {
-				ret = -EBUSY;
+			if (count == 0)
 				goto unlock_mutex;
-			}
 		}
 		ret = folio_test_clear_hwpoison(folio) ? 0 : -EBUSY;
-	} else if (ret < 0) {
-		if (ret == -EHWPOISON) {
+	} else if (ghp < 0) {
+		if (ghp == -EHWPOISON) {
 			ret = put_page_back_buddy(p) ? 0 : -EBUSY;
-		} else
+		} else {
+			ret = ghp;
 			unpoison_pr_info("Unpoison: failed to grab page %#lx\n",
 					 pfn, &unpoison_rs);
+		}
 	} else {
 		if (PageHuge(p)) {
 			huge = true;
 			count = folio_free_raw_hwp(folio, false);
 			if (count == 0) {
-				ret = -EBUSY;
 				folio_put(folio);
 				goto unlock_mutex;
 			}