linux-kernel - Re: [PATCH mmotm 3/5] huge tmpfs recovery: tweak shmem_getpage

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Message-ID: <20160421095021.422d54ed@canb.auug.org.au>
Date:	Thu, 21 Apr 2016 09:50:21 +1000
From:	Stephen Rothwell <sfr@...b.auug.org.au>
To:	Hugh Dickins <hughd@...gle.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Andres Lagar-Cavilla <andreslc@...gle.com>,
	Yang Shi <yang.shi@...aro.org>, Ning Qu <quning@...il.com>,
	Mika Penttila <mika.penttila@...tfour.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH mmotm 3/5] huge tmpfs recovery: tweak shmem_getpage_gfp
 to fill team fix

Hi Hugh,

On Sat, 16 Apr 2016 16:33:07 -0700 (PDT) Hugh Dickins <hughd@...gle.com> wrote:
>
> Please add this fix after my 27/31, your
> huge-tmpfs-recovery-tweak-shmem_getpage_gfp-to-fill-team.patch
> for later merging into it.  Great catch by Mika Penttila, a bug which
> prevented some unusual cases from being recovered into huge pages as
> intended: an initially sparse head would be set PageTeam only after
> this check.  But the check is guarding against a racing disband, which
> cannot happen before the head is published as PageTeam, plus we have
> an additional reference on the head which keeps it safe throughout:
> so very easily fixed.
> 
> Reported-by: Mika Penttila <mika.penttila@...tfour.com>
> Signed-off-by: Hugh Dickins <hughd@...gle.com>
> ---
>  mm/shmem.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -2938,7 +2938,7 @@ repeat:
>  			page = *pagep;
>  			lock_page(page);
>  			head = page - (index & (HPAGE_PMD_NR-1));
> -			if (!PageTeam(head)) {
> +			if (!PageTeam(head) && page != head) {
>  				error = -ENOENT;
>  				goto decused;
>  			}

Added to linux-next today.

-- 
Cheers,
Stephen Rothwell