mm: memory-failure: fix potential unexpected return value from unpoison_memory()

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: bf181c582588 ("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>

diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index ece5d48..b32d370 100644 (file)
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -2466,7 +2466,7 @@ 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,
@@ -2514,29 +2514,28 @@ 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;
                        }