The patch titled
Subject: mempolicy: fix a memory corruption by refcount imbalance in alloc_pages_vma()
has been removed from the -mm tree. Its filename was
mempolicy-fix-a-memory-corruption-by-refcount-imbalance-in-alloc_pages_vma.patch
This patch was dropped because it was merged into mainline or a subsystem tree
------------------------------------------------------
From: Mel Gorman <mgorman@xxxxxxx>
Subject: mempolicy: fix a memory corruption by refcount imbalance in alloc_pages_vma()
cc9a6c87 ("cpuset: mm: reduce large amounts of memory barrier related
damage v3") introduced a potential memory corruption. shmem_alloc_page()
uses a pseudo vma and it has one significant unique combination,
vma->vm_ops=NULL and vma->policy->flags & MPOL_F_SHARED.
get_vma_policy() does NOT increase a policy ref when vma->vm_ops=NULL and
mpol_cond_put() DOES decrease a policy ref when a policy has
MPOL_F_SHARED. Therefore, when a cpuset update race occurs,
alloc_pages_vma() falls in 'goto retry_cpuset' path, decrements the
reference count and frees the policy prematurely.
Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
Signed-off-by: Mel Gorman <mgorman@xxxxxxx>
Reviewed-by: Christoph Lameter <cl@xxxxxxxxx>
Cc: Josh Boyer <jwboyer@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/mempolicy.c | 12 +++++++++++-
1 file changed, 11 insertions(+), 1 deletion(-)
diff -puN mm/mempolicy.c~mempolicy-fix-a-memory-corruption-by-refcount-imbalance-in-alloc_pages_vma mm/mempolicy.c
--- a/mm/mempolicy.c~mempolicy-fix-a-memory-corruption-by-refcount-imbalance-in-alloc_pages_vma
+++ a/mm/mempolicy.c
@@ -1552,8 +1552,18 @@ struct mempolicy *get_vma_policy(struct
addr);
if (vpol)
pol = vpol;
- } else if (vma->vm_policy)
+ } else if (vma->vm_policy) {
pol = vma->vm_policy;
+
+ /*
+ * shmem_alloc_page() passes MPOL_F_SHARED policy with
+ * a pseudo vma whose vma->vm_ops=NULL. Take a reference
+ * count on these policies which will be dropped by
+ * mpol_cond_put() later
+ */
+ if (mpol_needs_cond_ref(pol))
+ mpol_get(pol);
+ }
}
if (!pol)
pol = &default_policy;
_
Patches currently in -mm which might be from mgorman@xxxxxxx are
origin.patch
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