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

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Date:	Sat, 16 Apr 2016 16:33:07 -0700 (PDT)
From:	Hugh Dickins <hughd@...gle.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
cc:	"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>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	Mika Penttila <mika.penttila@...tfour.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: [PATCH mmotm 3/5] huge tmpfs recovery: tweak shmem_getpage_gfp to
 fill team fix

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;
 			}