1 files changed, 44 insertions, 0 deletions

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 5bc0a96beb51..8a73708d59bb 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -1712,6 +1712,50 @@ bool init_nodemask_of_mempolicy(nodemask_t *mask)
 }
 #endif
 
+/*
+ * mempolicy_nodemask_intersects
+ *
+ * If tsk's mempolicy is "default" [NULL], return 'true' to indicate default
+ * policy.  Otherwise, check for intersection between mask and the policy
+ * nodemask for 'bind' or 'interleave' policy.  For 'perferred' or 'local'
+ * policy, always return true since it may allocate elsewhere on fallback.
+ *
+ * Takes task_lock(tsk) to prevent freeing of its mempolicy.
+ */
+bool mempolicy_nodemask_intersects(struct task_struct *tsk,
+                                        const nodemask_t *mask)
+{
+        struct mempolicy *mempolicy;
+        bool ret = true;
+
+        if (!mask)
+                return ret;
+        task_lock(tsk);
+        mempolicy = tsk->mempolicy;
+        if (!mempolicy)
+                goto out;
+
+        switch (mempolicy->mode) {
+        case MPOL_PREFERRED:
+                /*
+                 * MPOL_PREFERRED and MPOL_F_LOCAL are only preferred nodes to
+                 * allocate from, they may fallback to other nodes when oom.
+                 * Thus, it's possible for tsk to have allocated memory from
+                 * nodes in mask.
+                 */
+                break;
+        case MPOL_BIND:
+        case MPOL_INTERLEAVE:
+                ret = nodes_intersects(mempolicy->v.nodes, *mask);
+                break;
+        default:
+                BUG();
+        }
+out:
+        task_unlock(tsk);
+        return ret;
+}
+
 /* Allocate a page in interleaved policy.
    Own path because it needs to do special accounting. */
 static struct page *alloc_page_interleave(gfp_t gfp, unsigned order,