[PATCH mmotm 3/5] huge tmpfs recovery: tweak shmem_getpage_gfp to fill team fix

[Hugh Dickins]

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.pentt...@nextfour.com>
Signed-off-by: Hugh Dickins <hu...@google.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;
                        }