linux-kernel - Re: [PATCH stable 6.1] mm: Fix is_zero_page() usage in try_grab

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Message-ID: <aAAl5HdLYQl3nIjO@eldamar.lan>
Date: Wed, 16 Apr 2025 23:49:24 +0200
From: Salvatore Bonaccorso <carnil@...ian.org>
To: Alex Williamson <alex.williamson@...hat.com>
Cc: Milan Broz <gmazyland@...il.com>, stable@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Sasha Levin <sashal@...nel.org>
Subject: Re: [PATCH stable 6.1] mm: Fix is_zero_page() usage in
 try_grab_page()

Hi Alex,

On Wed, Apr 16, 2025 at 02:24:39PM -0600, Alex Williamson wrote:
> The backport of upstream commit c8070b787519 ("mm: Don't pin ZERO_PAGE
> in pin_user_pages()") into v6.1.130 noted below in Fixes does not
> account for commit 0f0892356fa1 ("mm: allow multiple error returns in
> try_grab_page()"), which changed the return value of try_grab_page()
> from bool to int.  Therefore returning 0, success in the upstream
> version, becomes an error here.  Fix the return value.
> 
> Fixes: 476c1dfefab8 ("mm: Don't pin ZERO_PAGE in pin_user_pages()")
> Link: https://lore.kernel.org/all/Z_6uhLQjJ7SSzI13@eldamar.lan
> Reported-by: Salvatore Bonaccorso <carnil@...ian.org>
> Reported-by: Milan Broz <gmazyland@...il.com>
> Cc: stable@...r.kernel.org
> Cc: linux-kernel@...r.kernel.org
> Cc: linux-mm@...ck.org
> Cc: Sasha Levin <sashal@...nel.org>
> Signed-off-by: Alex Williamson <alex.williamson@...hat.com>
> ---
>  mm/gup.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/gup.c b/mm/gup.c
> index b1daaa9d89aa..76a2b0943e2d 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -232,7 +232,7 @@ bool __must_check try_grab_page(struct page *page, unsigned int flags)
>  		 * and it is used in a *lot* of places.
>  		 */
>  		if (is_zero_page(page))
> -			return 0;
> +			return true;
>  
>  		/*
>  		 * Similar to try_grab_folio(): be sure to *also*
> -- 
> 2.48.1

Thank you, with your patch applied one test VM with a PCI passhtrough
configuration start again.

Tested-by: Salvatore Bonaccorso <carnil@...ian.org>

Regards,
Salvatore