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

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Date:   Thu, 21 Oct 2021 11:15:38 -0700
From:   Yang Shi <shy828301@...il.com>
To:     Nathan Chancellor <nathan@...nel.org>
Cc:     Naoya Horiguchi <naoya.horiguchi@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Linux MM <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        llvm@...ts.linux.dev, "kernelci.org bot" <bot@...nelci.org>
Subject: Re: [PATCH] mm/memory_failure: Initialize extra_pins in me_pagecache_clean()

On Thu, Oct 21, 2021 at 11:04 AM Nathan Chancellor <nathan@...nel.org> wrote:
>
> 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.

Thanks for catching this. Acked-by: Yang Shi <shy828301@...il.com>

>
>  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
>