cpuset: mm: reduce large amounts of memory barrier related damage v3

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

diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index 0b1712d..46a1d3c 100644 (file)
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -964,7 +964,6 @@ static void cpuset_change_task_nodemask(struct task_struct *tsk,
 {
        bool need_loop;
 
-repeat:
        /*
         * Allow tasks that have access to memory reserves because they have
         * been OOM killed to get memory anywhere.
@@ -983,45 +982,19 @@ repeat:
         */
        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);
 
-       /*
-        * ensure checking ->mems_allowed_change_disable after setting all new
-        * allowed nodes.
-        *
-        * the read-side task can see an nodemask with new allowed nodes and
-        * old allowed nodes. and if it allocates page when cpuset clears newly
-        * disallowed ones continuous, it can see the new allowed bits.
-        *
-        * And if setting all new allowed nodes is after the checking, setting
-        * all new allowed nodes and clearing newly disallowed ones will be done
-        * continuous, and the read-side task may find no node to alloc page.
-        */
-       smp_mb();
+       if (need_loop)
+               write_seqcount_begin(&tsk->mems_allowed_seq);
 
-       /*
-        * Allocation of memory is very fast, we needn't sleep when waiting
-        * for the read-side.
-        */
-       while (need_loop && ACCESS_ONCE(tsk->mems_allowed_change_disable)) {
-               task_unlock(tsk);
-               if (!task_curr(tsk))
-                       yield();
-               goto repeat;
-       }
-
-       /*
-        * ensure checking ->mems_allowed_change_disable before clearing all new
-        * disallowed nodes.
-        *
-        * if clearing newly disallowed bits before the checking, the read-side
-        * task may find no node to alloc page.
-        */
-       smp_mb();
+       nodes_or(tsk->mems_allowed, tsk->mems_allowed, *newmems);
+       mpol_rebind_task(tsk, newmems, MPOL_REBIND_STEP1);
 
        mpol_rebind_task(tsk, newmems, MPOL_REBIND_STEP2);
        tsk->mems_allowed = *newmems;
+
+       if (need_loop)
+               write_seqcount_end(&tsk->mems_allowed_seq);
+
        task_unlock(tsk);
 }