linux-kernel - Re: [PATCH] mm/mremap: fix uninitialized return code

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Message-ID: <bc7c9b8a-83e7-49f8-bf0a-2f2bb950b99d@lucifer.local>
Date: Wed, 5 Mar 2025 17:29:52 +0000
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Arnd Bergmann <arnd@...nel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
        "Liam R. Howlett" <Liam.Howlett@...cle.com>,
        Arnd Bergmann <arnd@...db.de>, Vlastimil Babka <vbabka@...e.cz>,
        Jann Horn <jannh@...gle.com>, Pedro Falcato <pedro.falcato@...il.com>,
        David Hildenbrand <david@...hat.com>,
        Kefeng Wang <wangkefeng.wang@...wei.com>,
        Jeff Xu <jeffxu@...omium.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/mremap: fix uninitialized return code

On Wed, Mar 05, 2025 at 06:27:56PM +0100, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@...db.de>
>
> The 'err' variable is set in a conditinal branch and is not
> set otherwise:
>
> mm/mremap.c:1017:7: error: variable 'err' is used uninitialized whenever 'if' condition is false [-Werror,-Wsometimes-uninitialized]
>  1017 |                 if (vma->vm_start != old_addr)
>
> Set it to zero before the initial value is set.
>
> Fixes: 3129f7896afb ("mm/mremap: initial refactor of move_vma()")
> Signed-off-by: Arnd Bergmann <arnd@...db.de>

Thanks for this, however this has already been fixed via Andrew doing a
fix-patch which should land in mm-unstable,-next soon (possibly tmr?).

This is entirely my bad btw, for some reason my compiler locally didn't
catch this even with CONFIG_WERROR on which _really_ surprises me...

> ---
>  mm/mremap.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/mm/mremap.c b/mm/mremap.c
> index 456849b9e7bd..9c51a2360d84 100644
> --- a/mm/mremap.c
> +++ b/mm/mremap.c
> @@ -1014,6 +1014,7 @@ static unsigned long prep_move_vma(struct vma_remap_struct *vrm)
>  		return -ENOMEM;
>
>  	if (vma->vm_ops && vma->vm_ops->may_split) {
> +		err = 0;
>  		if (vma->vm_start != old_addr)
>  			err = vma->vm_ops->may_split(vma, old_addr);
>  		if (!err && vma->vm_end != old_addr + old_len)
> --
> 2.39.5
>