linux-kernel - [PATCH] mm: shmem: fix uninitialized variable use in me_pagecache

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Message-Id: <20211022064748.4173718-1-arnd@kernel.org>
Date:   Fri, 22 Oct 2021 08:47:36 +0200
From:   Arnd Bergmann <arnd@...nel.org>
To:     Naoya Horiguchi <naoya.horiguchi@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Yang Shi <shy828301@...il.com>,
        Stephen Rothwell <sfr@...b.auug.org.au>
Cc:     Arnd Bergmann <arnd@...db.de>, Oscar Salvador <osalvador@...e.de>,
        Miaohe Lin <linmiaohe@...wei.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH] mm: shmem: fix uninitialized variable use in me_pagecache_clean()

From: Arnd Bergmann <arnd@...db.de>

It appears that the has_extra_refcount() is now in the wrong place:

mm/memory-failure.c:892:6: error: variable 'extra_pins' is used uninitialized whenever 'if' condition is true [-Werror,-Wsometimes-uninitialized]
        if (!mapping) {
            ^~~~~~~~
mm/memory-failure.c:915:32: note: uninitialized use occurs here
        if (has_extra_refcount(ps, p, extra_pins))
                                      ^~~~~~~~~~
mm/memory-failure.c:892:2: note: remove the 'if' if its condition is always false
        if (!mapping) {
        ^~~~~~~~~~~~~~~
mm/memory-failure.c:879:6: error: variable 'extra_pins' is used uninitialized whenever 'if' condition is true [-Werror,-Wsometimes-uninitialized]
        if (PageAnon(p)) {
            ^~~~~~~~~~~
mm/memory-failure.c:915:32: note: uninitialized use occurs here
        if (has_extra_refcount(ps, p, extra_pins))
                                      ^~~~~~~~~~
mm/memory-failure.c:879:2: note: remove the 'if' if its condition is always false
        if (PageAnon(p)) {
        ^~~~~~~~~~~~~~~~~~
mm/memory-failure.c:871:17: note: initialize the variable 'extra_pins' to silence this warning
        bool extra_pins;
                       ^
                        = 0

In both of those cases, we already set an error code and don't
need to override that one.

Fixes: d882a43a0011 ("mm: shmem: don't truncate page if memory failure happens")
Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
This is caused by a commit im -mm, so the commit ID is not stable.
If the fix is correct, I'd suggest folding it into the original
change
---
 mm/memory-failure.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index 3b04f0361a58..e8c38e27b753 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -909,12 +909,12 @@ static int me_pagecache_clean(struct page_state *ps, struct page *p)
 	 * Open: to take i_rwsem or not for this? Right now we don't.
 	 */
 	ret = truncate_error_page(p, page_to_pfn(p), mapping);
-out:
-	unlock_page(p);
-
 	if (has_extra_refcount(ps, p, extra_pins))
 		ret = MF_FAILED;
 
+out:
+	unlock_page(p);
+
 	return ret;
 }
 
-- 
2.29.2