linux-kernel - Re: [PATCH next] x86/mm: Fix uninitialized variable in register_page_bootmem

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Message-ID: <CAPTztWahPK5MLTxMnGH8woe1emM=QA=3pjy1ZCBBG+D39aLGog@mail.gmail.com>
Date: Wed, 12 Feb 2025 09:59:54 -0800
From: Frank van der Linden <fvdl@...gle.com>
To: Dan Carpenter <dan.carpenter@...aro.org>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>, Andy Lutomirski <luto@...nel.org>, 
	Peter Zijlstra <peterz@...radead.org>, Thomas Gleixner <tglx@...utronix.de>, 
	Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, x86@...nel.org, 
	"H. Peter Anvin" <hpa@...or.com>, Andrew Morton <akpm@...ux-foundation.org>, linux-kernel@...r.kernel.org, 
	kernel-janitors@...r.kernel.org
Subject: Re: [PATCH next] x86/mm: Fix uninitialized variable in register_page_bootmem_memmap()

On Wed, Feb 12, 2025 at 7:21 AM Dan Carpenter <dan.carpenter@...aro.org> wrote:
>
> Smatch complains that "next" could be uninitialized.  The "next"
> assignment was accidentally left out when we moved these lines to earlier
> in the function.
>
> Fixes: bdadaec1526d ("x86/mm: make register_page_bootmem_memmap handle PTE mappings")
> Signed-off-by: Dan Carpenter <dan.carpenter@...aro.org>
> ---
> This goes through the -mm tree.
>
>  arch/x86/mm/init_64.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
> index e7572af639a4..6e8e4ef5312a 100644
> --- a/arch/x86/mm/init_64.c
> +++ b/arch/x86/mm/init_64.c
> @@ -1600,8 +1600,10 @@ void register_page_bootmem_memmap(unsigned long section_nr,
>                 get_page_bootmem(section_nr, pud_page(*pud), MIX_SECTION_INFO);
>
>                 pmd = pmd_offset(pud, addr);
> -               if (pmd_none(*pmd))
> +               if (pmd_none(*pmd)) {
> +                       next = (addr + PAGE_SIZE) & PAGE_MASK;
>                         continue;
> +               }
>
>                 if (!boot_cpu_has(X86_FEATURE_PSE) || !pmd_leaf(*pmd)) {
>                         next = (addr + PAGE_SIZE) & PAGE_MASK;
> --
> 2.47.2
>

Thanks for catching that Dan. I believe Andrew took the series out of
mm-unstable because of some conflicts, and asked me to do a v4 for
mm-unstable. Would you mind if I just folded your change in to the v4
series?

As an aside, it seems that this function could use some cleanup. It
seems wrong to only advance by PAGE_SIZE when you encounter an
unpopulated p4d/pgd/pud/pmd. It should advance to the end of that
p4d/pgd/pud/pmd. I suppose that case won't happen in practice, though,
which is also why this hasn't caused me any issues.

- Frank