cpusets: stall when updating mems_allowed for mempolicy or disjoint nodemask

[pandora-kernel.git] / kernel / cpuset.c

diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index 9fe58c4..0b1712d 100644 (file)
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -123,6 +123,19 @@ static inline struct cpuset *task_cs(struct task_struct *task)
                            struct cpuset, css);
 }
 
+#ifdef CONFIG_NUMA
+static inline bool task_has_mempolicy(struct task_struct *task)
+{
+       return task->mempolicy;
+}
+#else
+static inline bool task_has_mempolicy(struct task_struct *task)
+{
+       return false;
+}
+#endif
+
+
 /* bits in struct cpuset flags field */
 typedef enum {
        CS_CPU_EXCLUSIVE,
@@ -949,7 +962,7 @@ static void cpuset_migrate_mm(struct mm_struct *mm, const nodemask_t *from,
 static void cpuset_change_task_nodemask(struct task_struct *tsk,
                                        nodemask_t *newmems)
 {
-       bool masks_disjoint = !nodes_intersects(*newmems, tsk->mems_allowed);
+       bool need_loop;
 
 repeat:
        /*
@@ -962,6 +975,14 @@ repeat:
                return;
 
        task_lock(tsk);
+       /*
+        * Determine if a loop is necessary if another thread is doing
+        * get_mems_allowed().  If at least one node remains unchanged and
+        * tsk does not have a mempolicy, then an empty nodemask will not be
+        * possible when mems_allowed is larger than a word.
+        */
+       need_loop = task_has_mempolicy(tsk) ||
+                       !nodes_intersects(*newmems, tsk->mems_allowed);
        nodes_or(tsk->mems_allowed, tsk->mems_allowed, *newmems);
        mpol_rebind_task(tsk, newmems, MPOL_REBIND_STEP1);
 
@@ -981,11 +1002,9 @@ repeat:
 
        /*
         * Allocation of memory is very fast, we needn't sleep when waiting
-        * for the read-side.  No wait is necessary, however, if at least one
-        * node remains unchanged.
+        * for the read-side.
         */
-       while (masks_disjoint &&
-                       ACCESS_ONCE(tsk->mems_allowed_change_disable)) {
+       while (need_loop && ACCESS_ONCE(tsk->mems_allowed_change_disable)) {
                task_unlock(tsk);
                if (!task_curr(tsk))
                        yield();