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

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Message-ID: <2025042243-glider-refurbish-c0d1@gregkh>
Date: Tue, 22 Apr 2025 10:01:49 +0200
From: Greg KH <greg@...ah.com>
To: Salvatore Bonaccorso <carnil@...ian.org>
Cc: Alex Williamson <alex.williamson@...hat.com>,
	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()

On Wed, Apr 16, 2025 at 11:49:24PM +0200, Salvatore Bonaccorso wrote:
> 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>

Now queued up, thanks.

greg k-h