linux-kernel - Re: [PATCH v2] mm/gup: fix gup_pud

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Date:   Wed, 7 Dec 2022 20:08:41 -0800
From:   Saurabh Singh Sengar <ssengar@...ux.microsoft.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     ssengar@...rosoft.com, yuzhao@...gle.com, jack@...e.cz,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        jostarks@...rosoft.com
Subject: Re: [PATCH v2] mm/gup: fix gup_pud_range() for dax

On Wed, Dec 07, 2022 at 01:31:30PM -0800, Andrew Morton wrote:
> On Tue,  6 Dec 2022 22:00:53 -0800 Saurabh Sengar <ssengar@...ux.microsoft.com> wrote:
> 
> > From: John Starks <jostarks@...rosoft.com>
> > 
> > For dax pud, pud_huge() returns true on x86. So the function works as long
> > as hugetlb is configured. However, dax doesn't depend on hugetlb.
> > Commit 414fd080d125 ("mm/gup: fix gup_pmd_range() for dax") fixed
> > devmap-backed huge PMDs, but missed devmap-backed huge PUDs. Fix this as
> > well.
> > 
> > This fixes the below kernel panic:
> > 
> > ...
> >
> > Fixes: 414fd080d125 ("mm/gup: fix gup_pmd_range() for dax")
> 
> Feb 2019.
> 
> > Signed-off-by: John Starks <jostarks@...rosoft.com>
> > Signed-off-by: Saurabh Sengar <ssengar@...ux.microsoft.com>
> > ---
> >  mm/gup.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/mm/gup.c b/mm/gup.c
> > index c2c2c6d..e776540 100644
> > --- a/mm/gup.c
> > +++ b/mm/gup.c
> > @@ -2765,7 +2765,7 @@ static int gup_pud_range(p4d_t *p4dp, p4d_t p4d, unsigned long addr, unsigned lo
> >  		next = pud_addr_end(addr, end);
> >  		if (unlikely(!pud_present(pud)))
> >  			return 0;
> > -		if (unlikely(pud_huge(pud))) {
> > +		if (unlikely(pud_huge(pud) || pud_devmap(pud))) {
> >  			if (!gup_huge_pud(pud, pudp, addr, next, flags,
> >  					  pages, nr))
> >  				return 0;
> 
> I assume this should be backported into -stable kernels?
That would be helpful, thanks.