mempolicy: fixup Fallback for Default Shmem Policy

get_vma_policy() is not handling fallback to task policy correctly when the
get_policy() vm_op returns NULL.  The NULL overwrites the 'pol' variable that
was holding the fallback task mempolicy.  So, it was falling back directly to
system default policy.

Fix get_vma_policy() to use only non-NULL policy returned from the vma
get_policy op.

shm_get_policy() was falling back to current task's mempolicy if the "backing
file system" [tmpfs vs hugetlbfs] does not support the get_policy vm_op and
the vma policy is null.  This is incorrect for show_numa_maps() which is
likely querying the numa_maps of some task other than current.  Remove this
fallback.

Signed-off-by: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Christoph Lameter <clameter@sgi.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Mel Gorman <mel@csn.ul.ie>
Cc: Andi Kleen <ak@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 1 insertions, 2 deletions

diff --git a/ipc/shm.c b/ipc/shm.c
index cc63fae..8d1b2c4 100644
--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -274,8 +274,7 @@ static struct mempolicy *shm_get_policy(struct vm_area_struct *vma,
 	else if (vma->vm_policy) {
 		pol = vma->vm_policy;
 		mpol_get(pol);	/* get_vma_policy() expects this */
-	} else
-		pol = current->mempolicy;
+	}
 	return pol;
 }
 #endif