mempolicy: disallow static or relative flags for local preferred mode

MPOL_F_STATIC_NODES and MPOL_F_RELATIVE_NODES don't mean anything for
MPOL_PREFERRED policies that were created with an empty nodemask (for purely
local allocations).  They'll never be invalidated because the allowed mems of
a task changes or need to be rebound relative to a cpuset's placement.

Also fixes a bug identified by Lee Schermerhorn that disallowed empty
nodemasks to be passed to MPOL_PREFERRED to specify local allocations.  [A
different, somewhat incomplete, patch already existed in 25-rc5-mm1.]

Cc: Paul Jackson <pj@sgi.com>
Cc: Christoph Lameter <clameter@sgi.com>
Cc: Lee Schermerhorn <Lee.Schermerhorn@hp.com>
Cc: Andi Kleen <ak@suse.de>
Cc: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Lee Schermerhorn <lee.schermerhorn@hp.com>
Signed-off-by: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 40 insertions, 18 deletions

diff --git a/Documentation/vm/numa_memory_policy.txt b/Documentation/vm/numa_memory_policy.txt
index 706410dfb9e5..1c7dd21623d2 100644
--- a/Documentation/vm/numa_memory_policy.txt
+++ b/Documentation/vm/numa_memory_policy.txt
@@ -205,6 +205,12 @@ Components of Memory Policies
             local allocation for a specific range of addresses--i.e. for
             VMA policies.
 
+            It is possible for the user to specify that local allocation is
+            always preferred by passing an empty nodemask with this mode.
+            If an empty nodemask is passed, the policy cannot use the
+            MPOL_F_STATIC_NODES or MPOL_F_RELATIVE_NODES flags described
+            below.
+
         MPOL_INTERLEAVED:  This mode specifies that page allocations be
         interleaved, on a page granularity, across the nodes specified in
         the policy.  This mode also behaves slightly differently, based on
@@ -254,7 +260,10 @@ Components of Memory Policies
             occurs over that node.  If no nodes from the user's nodemask are
             now allowed, the Default behavior is used.
 
-            MPOL_F_STATIC_NODES cannot be used with MPOL_F_RELATIVE_NODES.
+            MPOL_F_STATIC_NODES cannot be combined with the
+            MPOL_F_RELATIVE_NODES flag.  It also cannot be used for
+            MPOL_PREFERRED policies that were created with an empty nodemask
+            (local allocation).
 
         MPOL_F_RELATIVE_NODES:  This flag specifies that the nodemask passed
         by the user will be mapped relative to the set of the task or VMA's
@@ -301,7 +310,10 @@ Components of Memory Policies
             set of memory nodes allowed by the task's cpuset, as that may
             change over time.
 
-            MPOL_F_RELATIVE_NODES cannot be used with MPOL_F_STATIC_NODES.
+            MPOL_F_RELATIVE_NODES cannot be combined with the
+            MPOL_F_STATIC_NODES flag.  It also cannot be used for
+            MPOL_PREFERRED policies that were created with an empty nodemask
+            (local allocation).
 
 MEMORY POLICY APIs
 
diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index a94d994eaaa8..c1b907789d84 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -181,27 +181,43 @@ static struct mempolicy *mpol_new(unsigned short mode, unsigned short flags,
 {
         struct mempolicy *policy;
         nodemask_t cpuset_context_nmask;
-        int localalloc = 0;
         int ret;
 
         pr_debug("setting mode %d flags %d nodes[0] %lx\n",
                  mode, flags, nodes ? nodes_addr(*nodes)[0] : -1);
 
-        if (mode == MPOL_DEFAULT)
-                return NULL;
-        if (!nodes || nodes_empty(*nodes)) {
-                if (mode != MPOL_PREFERRED)
+        if (mode == MPOL_DEFAULT) {
+                if (nodes && !nodes_empty(*nodes))
                         return ERR_PTR(-EINVAL);
-                localalloc = 1; /* special case:  no mode flags */
+                return NULL;
         }
+        VM_BUG_ON(!nodes);
+
+        /*
+         * MPOL_PREFERRED cannot be used with MPOL_F_STATIC_NODES or
+         * MPOL_F_RELATIVE_NODES if the nodemask is empty (local allocation).
+         * All other modes require a valid pointer to a non-empty nodemask.
+         */
+        if (mode == MPOL_PREFERRED) {
+                if (nodes_empty(*nodes)) {
+                        if (((flags & MPOL_F_STATIC_NODES) ||
+                             (flags & MPOL_F_RELATIVE_NODES)))
+                                return ERR_PTR(-EINVAL);
+                        nodes = NULL;   /* flag local alloc */
+                }
+        } else if (nodes_empty(*nodes))
+                return ERR_PTR(-EINVAL);
         policy = kmem_cache_alloc(policy_cache, GFP_KERNEL);
         if (!policy)
                 return ERR_PTR(-ENOMEM);
         atomic_set(&policy->refcnt, 1);
         policy->policy = mode;
+        policy->flags = flags;
 
-        if (!localalloc) {
-                policy->flags = flags;
+        if (nodes) {
+                /*
+                 * cpuset related setup doesn't apply to local allocation
+                 */
                 cpuset_update_task_memory_state();
                 if (flags & MPOL_F_RELATIVE_NODES)
                         mpol_relative_nodemask(&cpuset_context_nmask, nodes,
@@ -217,7 +233,7 @@ static struct mempolicy *mpol_new(unsigned short mode, unsigned short flags,
         }
 
         ret = mpol_ops[mode].create(policy,
-                                localalloc ? NULL : &cpuset_context_nmask);
+                                nodes ? &cpuset_context_nmask : NULL);
         if (ret < 0) {
                 kmem_cache_free(policy_cache, policy);
                 return ERR_PTR(ret);
@@ -259,10 +275,6 @@ static void mpol_rebind_preferred(struct mempolicy *pol,
 {
         nodemask_t tmp;
 
-        /*
-         * check 'STATIC_NODES first, as preferred_node == -1 may be
-         * a temporary, "fallback" state for this policy.
-         */
         if (pol->flags & MPOL_F_STATIC_NODES) {
                 int node = first_node(pol->w.user_nodemask);
 
@@ -270,12 +282,10 @@ static void mpol_rebind_preferred(struct mempolicy *pol,
                         pol->v.preferred_node = node;
                 else
                         pol->v.preferred_node = -1;
-        } else if (pol->v.preferred_node == -1) {
-                return; /* no remap required for explicit local alloc */
         } else if (pol->flags & MPOL_F_RELATIVE_NODES) {
                 mpol_relative_nodemask(&tmp, &pol->w.user_nodemask, nodes);
                 pol->v.preferred_node = first_node(tmp);
-        } else {
+        } else if (pol->v.preferred_node != -1) {
                 pol->v.preferred_node = node_remap(pol->v.preferred_node,
                                                    pol->w.cpuset_mems_allowed,
                                                    *nodes);