Merge branch 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull scheduler fixes from Ingo Molnar:
 "Thiscontains misc fixes: preempt_schedule_common() and io_schedule()
  recursion fixes, sched/dl fixes, a completion_done() revert, two
  sched/rt fixes and a comment update patch"

* 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  sched/rt: Avoid obvious configuration fail
  sched/autogroup: Fix failure to set cpu.rt_runtime_us
  sched/dl: Do update_rq_clock() in yield_task_dl()
  sched: Prevent recursion in io_schedule()
  sched/completion: Serialize completion_done() with complete()
  sched: Fix preempt_schedule_common() triggering tracing recursion
  sched/dl: Prevent enqueue of a sleeping task in dl_task_timer()
  sched: Make dl_task_time() use task_rq_lock()
  sched: Clarify ordering between task_rq_lock() and move_queued_task()

5 files changed, 148 insertions, 99 deletions

diff --git a/kernel/sched/auto_group.c b/kernel/sched/auto_group.c
index 8a2e230fb86a..eae160dd669d 100644
--- a/kernel/sched/auto_group.c
+++ b/kernel/sched/auto_group.c
@@ -87,8 +87,7 @@ static inline struct autogroup *autogroup_create(void)
          * so we don't have to move tasks around upon policy change,
          * or flail around trying to allocate bandwidth on the fly.
          * A bandwidth exception in __sched_setscheduler() allows
-         * the policy change to proceed.  Thereafter, task_group()
-         * returns &root_task_group, so zero bandwidth is required.
+         * the policy change to proceed.
          */
         free_rt_sched_group(tg);
         tg->rt_se = root_task_group.rt_se;
@@ -115,9 +114,6 @@ bool task_wants_autogroup(struct task_struct *p, struct task_group *tg)
         if (tg != &root_task_group)
                 return false;
 
-        if (p->sched_class != &fair_sched_class)
-                return false;
-
         /*
          * We can only assume the task group can't go away on us if
          * autogroup_move_group() can see us on ->thread_group list.
diff --git a/kernel/sched/completion.c b/kernel/sched/completion.c
index 7052d3fd4e7b..8d0f35debf35 100644
--- a/kernel/sched/completion.c
+++ b/kernel/sched/completion.c
@@ -274,7 +274,7 @@ bool try_wait_for_completion(struct completion *x)
          * first without taking the lock so we can
          * return early in the blocking case.
          */
-        if (!ACCESS_ONCE(x->done))
+        if (!READ_ONCE(x->done))
                 return 0;
 
         spin_lock_irqsave(&x->wait.lock, flags);
@@ -297,6 +297,21 @@ EXPORT_SYMBOL(try_wait_for_completion);
  */
 bool completion_done(struct completion *x)
 {
-        return !!ACCESS_ONCE(x->done);
+        if (!READ_ONCE(x->done))
+                return false;
+
+        /*
+         * If ->done, we need to wait for complete() to release ->wait.lock
+         * otherwise we can end up freeing the completion before complete()
+         * is done referencing it.
+         *
+         * The RMB pairs with complete()'s RELEASE of ->wait.lock and orders
+         * the loads of ->done and ->wait.lock such that we cannot observe
+         * the lock before complete() acquires it while observing the ->done
+         * after it's acquired the lock.
+         */
+        smp_rmb();
+        spin_unlock_wait(&x->wait.lock);
+        return true;
 }
 EXPORT_SYMBOL(completion_done);
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 13049aac05a6..f0f831e8a345 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -307,66 +307,6 @@ __read_mostly int scheduler_running;
 int sysctl_sched_rt_runtime = 950000;
 
 /*
- * __task_rq_lock - lock the rq @p resides on.
- */
-static inline struct rq *__task_rq_lock(struct task_struct *p)
-        __acquires(rq->lock)
-{
-        struct rq *rq;
-
-        lockdep_assert_held(&p->pi_lock);
-
-        for (;;) {
-                rq = task_rq(p);
-                raw_spin_lock(&rq->lock);
-                if (likely(rq == task_rq(p) && !task_on_rq_migrating(p)))
-                        return rq;
-                raw_spin_unlock(&rq->lock);
-
-                while (unlikely(task_on_rq_migrating(p)))
-                        cpu_relax();
-        }
-}
-
-/*
- * task_rq_lock - lock p->pi_lock and lock the rq @p resides on.
- */
-static struct rq *task_rq_lock(struct task_struct *p, unsigned long *flags)
-        __acquires(p->pi_lock)
-        __acquires(rq->lock)
-{
-        struct rq *rq;
-
-        for (;;) {
-                raw_spin_lock_irqsave(&p->pi_lock, *flags);
-                rq = task_rq(p);
-                raw_spin_lock(&rq->lock);
-                if (likely(rq == task_rq(p) && !task_on_rq_migrating(p)))
-                        return rq;
-                raw_spin_unlock(&rq->lock);
-                raw_spin_unlock_irqrestore(&p->pi_lock, *flags);
-
-                while (unlikely(task_on_rq_migrating(p)))
-                        cpu_relax();
-        }
-}
-
-static void __task_rq_unlock(struct rq *rq)
-        __releases(rq->lock)
-{
-        raw_spin_unlock(&rq->lock);
-}
-
-static inline void
-task_rq_unlock(struct rq *rq, struct task_struct *p, unsigned long *flags)
-        __releases(rq->lock)
-        __releases(p->pi_lock)
-{
-        raw_spin_unlock(&rq->lock);
-        raw_spin_unlock_irqrestore(&p->pi_lock, *flags);
-}
-
-/*
  * this_rq_lock - lock this runqueue and disable interrupts.
  */
 static struct rq *this_rq_lock(void)
@@ -2899,7 +2839,7 @@ void __sched schedule_preempt_disabled(void)
         preempt_disable();
 }
 
-static void preempt_schedule_common(void)
+static void __sched notrace preempt_schedule_common(void)
 {
         do {
                 __preempt_count_add(PREEMPT_ACTIVE);
@@ -4418,36 +4358,29 @@ EXPORT_SYMBOL_GPL(yield_to);
  * This task is about to go to sleep on IO. Increment rq->nr_iowait so
  * that process accounting knows that this is a task in IO wait state.
  */
-void __sched io_schedule(void)
-{
-        struct rq *rq = raw_rq();
-
-        delayacct_blkio_start();
-        atomic_inc(&rq->nr_iowait);
-        blk_flush_plug(current);
-        current->in_iowait = 1;
-        schedule();
-        current->in_iowait = 0;
-        atomic_dec(&rq->nr_iowait);
-        delayacct_blkio_end();
-}
-EXPORT_SYMBOL(io_schedule);
-
 long __sched io_schedule_timeout(long timeout)
 {
-        struct rq *rq = raw_rq();
+        int old_iowait = current->in_iowait;
+        struct rq *rq;
         long ret;
 
+        current->in_iowait = 1;
+        if (old_iowait)
+                blk_schedule_flush_plug(current);
+        else
+                blk_flush_plug(current);
+
         delayacct_blkio_start();
+        rq = raw_rq();
         atomic_inc(&rq->nr_iowait);
-        blk_flush_plug(current);
-        current->in_iowait = 1;
         ret = schedule_timeout(timeout);
-        current->in_iowait = 0;
+        current->in_iowait = old_iowait;
         atomic_dec(&rq->nr_iowait);
         delayacct_blkio_end();
+
         return ret;
 }
+EXPORT_SYMBOL(io_schedule_timeout);
 
 /**
  * sys_sched_get_priority_max - return maximum RT priority.
@@ -7642,6 +7575,12 @@ static inline int tg_has_rt_tasks(struct task_group *tg)
 {
         struct task_struct *g, *p;
 
+        /*
+         * Autogroups do not have RT tasks; see autogroup_create().
+         */
+        if (task_group_is_autogroup(tg))
+                return 0;
+
         for_each_process_thread(g, p) {
                 if (rt_task(p) && task_group(p) == tg)
                         return 1;
@@ -7734,6 +7673,17 @@ static int tg_set_rt_bandwidth(struct task_group *tg,
 {
         int i, err = 0;
 
+        /*
+         * Disallowing the root group RT runtime is BAD, it would disallow the
+         * kernel creating (and or operating) RT threads.
+         */
+        if (tg == &root_task_group && rt_runtime == 0)
+                return -EINVAL;
+
+        /* No period doesn't make any sense. */
+        if (rt_period == 0)
+                return -EINVAL;
+
         mutex_lock(&rt_constraints_mutex);
         read_lock(&tasklist_lock);
         err = __rt_schedulable(tg, rt_period, rt_runtime);
@@ -7790,9 +7740,6 @@ static int sched_group_set_rt_period(struct task_group *tg, long rt_period_us)
         rt_period = (u64)rt_period_us * NSEC_PER_USEC;
         rt_runtime = tg->rt_bandwidth.rt_runtime;
 
-        if (rt_period == 0)
-                return -EINVAL;
-
         return tg_set_rt_bandwidth(tg, rt_period, rt_runtime);
 }
 
diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index a027799ae130..3fa8fa6d9403 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -511,16 +511,10 @@ static enum hrtimer_restart dl_task_timer(struct hrtimer *timer)
                                                      struct sched_dl_entity,
                                                      dl_timer);
         struct task_struct *p = dl_task_of(dl_se);
+        unsigned long flags;
         struct rq *rq;
-again:
-        rq = task_rq(p);
-        raw_spin_lock(&rq->lock);
 
-        if (rq != task_rq(p)) {
-                /* Task was moved, retrying. */
-                raw_spin_unlock(&rq->lock);
-                goto again;
-        }
+        rq = task_rq_lock(current, &flags);
 
         /*
          * We need to take care of several possible races here:
@@ -541,6 +535,26 @@ again:
 
         sched_clock_tick();
         update_rq_clock(rq);
+
+        /*
+         * If the throttle happened during sched-out; like:
+         *
+         *   schedule()
+         *     deactivate_task()
+         *       dequeue_task_dl()
+         *         update_curr_dl()
+         *           start_dl_timer()
+         *         __dequeue_task_dl()
+         *     prev->on_rq = 0;
+         *
+         * We can be both throttled and !queued. Replenish the counter
+         * but do not enqueue -- wait for our wakeup to do that.
+         */
+        if (!task_on_rq_queued(p)) {
+                replenish_dl_entity(dl_se, dl_se);
+                goto unlock;
+        }
+
         enqueue_task_dl(rq, p, ENQUEUE_REPLENISH);
         if (dl_task(rq->curr))
                 check_preempt_curr_dl(rq, p, 0);
@@ -555,7 +569,7 @@ again:
                 push_dl_task(rq);
 #endif
 unlock:
-        raw_spin_unlock(&rq->lock);
+        task_rq_unlock(rq, current, &flags);
 
         return HRTIMER_NORESTART;
 }
@@ -898,6 +912,7 @@ static void yield_task_dl(struct rq *rq)
                 rq->curr->dl.dl_yielded = 1;
                 p->dl.runtime = 0;
         }
+        update_rq_clock(rq);
         update_curr_dl(rq);
 }
 
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 0870db23d79c..dc0f435a2779 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1380,6 +1380,82 @@ static inline void sched_avg_update(struct rq *rq) { }
 
 extern void start_bandwidth_timer(struct hrtimer *period_timer, ktime_t period);
 
+/*
+ * __task_rq_lock - lock the rq @p resides on.
+ */
+static inline struct rq *__task_rq_lock(struct task_struct *p)
+        __acquires(rq->lock)
+{
+        struct rq *rq;
+
+        lockdep_assert_held(&p->pi_lock);
+
+        for (;;) {
+                rq = task_rq(p);
+                raw_spin_lock(&rq->lock);
+                if (likely(rq == task_rq(p) && !task_on_rq_migrating(p)))
+                        return rq;
+                raw_spin_unlock(&rq->lock);
+
+                while (unlikely(task_on_rq_migrating(p)))
+                        cpu_relax();
+        }
+}
+
+/*
+ * task_rq_lock - lock p->pi_lock and lock the rq @p resides on.
+ */
+static inline struct rq *task_rq_lock(struct task_struct *p, unsigned long *flags)
+        __acquires(p->pi_lock)
+        __acquires(rq->lock)
+{
+        struct rq *rq;
+
+        for (;;) {
+                raw_spin_lock_irqsave(&p->pi_lock, *flags);
+                rq = task_rq(p);
+                raw_spin_lock(&rq->lock);
+                /*
+                 *      move_queued_task()              task_rq_lock()
+                 *
+                 *      ACQUIRE (rq->lock)
+                 *      [S] ->on_rq = MIGRATING         [L] rq = task_rq()
+                 *      WMB (__set_task_cpu())          ACQUIRE (rq->lock);
+                 *      [S] ->cpu = new_cpu             [L] task_rq()
+                 *                                      [L] ->on_rq
+                 *      RELEASE (rq->lock)
+                 *
+                 * If we observe the old cpu in task_rq_lock, the acquire of
+                 * the old rq->lock will fully serialize against the stores.
+                 *
+                 * If we observe the new cpu in task_rq_lock, the acquire will
+                 * pair with the WMB to ensure we must then also see migrating.
+                 */
+                if (likely(rq == task_rq(p) && !task_on_rq_migrating(p)))
+                        return rq;
+                raw_spin_unlock(&rq->lock);
+                raw_spin_unlock_irqrestore(&p->pi_lock, *flags);
+
+                while (unlikely(task_on_rq_migrating(p)))
+                        cpu_relax();
+        }
+}
+
+static inline void __task_rq_unlock(struct rq *rq)
+        __releases(rq->lock)
+{
+        raw_spin_unlock(&rq->lock);
+}
+
+static inline void
+task_rq_unlock(struct rq *rq, struct task_struct *p, unsigned long *flags)
+        __releases(rq->lock)
+        __releases(p->pi_lock)
+{
+        raw_spin_unlock(&rq->lock);
+        raw_spin_unlock_irqrestore(&p->pi_lock, *flags);
+}
+
 #ifdef CONFIG_SMP
 #ifdef CONFIG_PREEMPT