Merge branch 'core-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel...

[sfrench/cifs-2.6.git] / kernel / sched.c

diff --git a/kernel/sched.c b/kernel/sched.c
index 4508fe7048be5d91ee5a01daef3fe9de8d37b909..3a8fb30a91b1bba639e164d8f34209a0497ae9fd 100644 (file)
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -2320,14 +2320,12 @@ static int select_fallback_rq(int cpu, struct task_struct *p)
 }
 
 /*
- * Called from:
+ * Gets called from 3 sites (exec, fork, wakeup), since it is called without
+ * holding rq->lock we need to ensure ->cpus_allowed is stable, this is done
+ * by:
  *
- *  - fork, @p is stable because it isn't on the tasklist yet
- *
- *  - exec, @p is unstable, retry loop
- *
- *  - wake-up, we serialize ->cpus_allowed against TASK_WAKING so
- *             we should be good.
+ *  exec:           is unstable, retry loop
+ *  fork & wake-up: serialize ->cpus_allowed against TASK_WAKING
  */
 static inline
 int select_task_rq(struct task_struct *p, int sd_flags, int wake_flags)
@@ -2620,9 +2618,6 @@ void sched_fork(struct task_struct *p, int clone_flags)
        if (p->sched_class->task_fork)
                p->sched_class->task_fork(p);
 
-#ifdef CONFIG_SMP
-       cpu = select_task_rq(p, SD_BALANCE_FORK, 0);
-#endif
        set_task_cpu(p, cpu);
 
 #if defined(CONFIG_SCHEDSTATS) || defined(CONFIG_TASK_DELAY_ACCT)
@@ -2652,6 +2647,21 @@ void wake_up_new_task(struct task_struct *p, unsigned long clone_flags)
 {
        unsigned long flags;
        struct rq *rq;
+       int cpu = get_cpu();
+
+#ifdef CONFIG_SMP
+       /*
+        * Fork balancing, do it here and not earlier because:
+        *  - cpus_allowed can change in the fork path
+        *  - any previously selected cpu might disappear through hotplug
+        *
+        * We still have TASK_WAKING but PF_STARTING is gone now, meaning
+        * ->cpus_allowed is stable, we have preemption disabled, meaning
+        * cpu_online_mask is stable.
+        */
+       cpu = select_task_rq(p, SD_BALANCE_FORK, 0);
+       set_task_cpu(p, cpu);
+#endif
 
        rq = task_rq_lock(p, &flags);
        BUG_ON(p->state != TASK_WAKING);
@@ -2665,6 +2675,7 @@ void wake_up_new_task(struct task_struct *p, unsigned long clone_flags)
                p->sched_class->task_woken(rq, p);
 #endif
        task_rq_unlock(rq, &flags);
+       put_cpu();
 }
 
 #ifdef CONFIG_PREEMPT_NOTIFIERS
@@ -7139,14 +7150,18 @@ int set_cpus_allowed_ptr(struct task_struct *p, const struct cpumask *new_mask)
         * the ->cpus_allowed mask from under waking tasks, which would be
         * possible when we change rq->lock in ttwu(), so synchronize against
         * TASK_WAKING to avoid that.
+        *
+        * Make an exception for freshly cloned tasks, since cpuset namespaces
+        * might move the task about, we have to validate the target in
+        * wake_up_new_task() anyway since the cpu might have gone away.
         */
 again:
-       while (p->state == TASK_WAKING)
+       while (p->state == TASK_WAKING && !(p->flags & PF_STARTING))
                cpu_relax();
 
        rq = task_rq_lock(p, &flags);
 
-       if (p->state == TASK_WAKING) {
+       if (p->state == TASK_WAKING && !(p->flags & PF_STARTING)) {
                task_rq_unlock(rq, &flags);
                goto again;
        }