Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
From:   Miaohe Lin <linmiaohe@huawei.com>
To:     <akpm@linux-foundation.org>, <naoya.horiguchi@nec.com>
CC:     <willy@infradead.org>, <linux-mm@kvack.org>,
        <linux-kernel@vger.kernel.org>, <linmiaohe@huawei.com>
Subject: [PATCH v2 2/4] mm: memory-failure: fix potential unexpected return value from unpoison_memory()
Date:   Thu, 27 Jul 2023 19:56:41 +0800
Message-ID: <20230727115643.639741-3-linmiaohe@huawei.com>
In-Reply-To: <20230727115643.639741-1-linmiaohe@huawei.com>
References: <20230727115643.639741-1-linmiaohe@huawei.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 7BIT
Content-Type:   text/plain; charset=US-ASCII
Precedence: bulk

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.

Fixes: bf181c582588 ("mm/hwpoison: fix unpoison_memory()")
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
---
 mm/memory-failure.c | 19 +++++++++----------
 1 file changed, 9 insertions(+), 10 deletions(-)

diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index a114c8c3039c..4a3e88c15631 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -2502,7 +2502,7 @@ 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,
@@ -2550,29 +2550,28 @@ 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;
 			}
-- 
2.33.0