linux-kernel - [PATCH] mm/memory_failure: Initialize extra_pins in me_pagecache

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Message-Id: <20211021180336.2328086-1-nathan@kernel.org>
Date:   Thu, 21 Oct 2021 11:03:37 -0700
From:   Nathan Chancellor <nathan@...nel.org>
To:     Naoya Horiguchi <naoya.horiguchi@....com>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     Nick Desaulniers <ndesaulniers@...gle.com>,
        Yang Shi <shy828301@...il.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, llvm@...ts.linux.dev,
        Nathan Chancellor <nathan@...nel.org>,
        "kernelci.org bot" <bot@...nelci.org>
Subject: [PATCH] mm/memory_failure: Initialize extra_pins in me_pagecache_clean()

Clang warns:

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
2 errors generated.

Initialize extra_pins to false so that it is not used uninitialized.

Fixes: d882a43a0011 ("mm: shmem: don't truncate page if memory failure happens")
Link: https://github.com/ClangBuiltLinux/linux/issues/1487
Reported-by: "kernelci.org bot" <bot@...nelci.org>
Signed-off-by: Nathan Chancellor <nathan@...nel.org>
---

I am aware the fixes tag is not stable. It is there to convey this
should be squashed into mm-shmem-dont-truncate-page-if-memory-failure-happens.patch.

 mm/memory-failure.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index 3b04f0361a58..dba5f0098165 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -868,7 +868,7 @@ static int me_pagecache_clean(struct page_state *ps, struct page *p)
 {
 	int ret;
 	struct address_space *mapping;
-	bool extra_pins;
+	bool extra_pins = false;
 
 	delete_from_lru_cache(p);
 
-- 
2.33.1.637.gf443b226ca