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

Pull scheduler fixes from Thomas Gleixner:
 "This updates contains the following changes:

   - Fix a signal handling regression in the bit wait functions.

   - Avoid false positive warnings in the wakeup path.

   - Initialize the scheduler root domain properly.

   - Handle gtime calculations in proc/$PID/stat proper.

   - Add more documentation for the barriers in try_to_wake_up().

   - Fix a subtle race in try_to_wake_up() which might cause a task to
     be scheduled on two cpus

   - Compile static helper function only when it is used"

* 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  sched/core: Fix an SMP ordering race in try_to_wake_up() vs. schedule()
  sched/core: Better document the try_to_wake_up() barriers
  sched/cputime: Fix invalid gtime in proc
  sched/core: Clear the root_domain cpumasks in init_rootdomain()
  sched/core: Remove false-positive warning from wake_up_process()
  sched/wait: Fix signal handling in bit wait helpers
  sched/rt: Hide the push_irq_work_func() declaration

5 files changed, 45 insertions, 15 deletions

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 4d568ac9319e..7063c6a07440 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1947,13 +1947,38 @@ try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags)
 
 #ifdef CONFIG_SMP
         /*
+         * Ensure we load p->on_cpu _after_ p->on_rq, otherwise it would be
+         * possible to, falsely, observe p->on_cpu == 0.
+         *
+         * One must be running (->on_cpu == 1) in order to remove oneself
+         * from the runqueue.
+         *
+         *  [S] ->on_cpu = 1;   [L] ->on_rq
+         *      UNLOCK rq->lock
+         *                      RMB
+         *      LOCK   rq->lock
+         *  [S] ->on_rq = 0;    [L] ->on_cpu
+         *
+         * Pairs with the full barrier implied in the UNLOCK+LOCK on rq->lock
+         * from the consecutive calls to schedule(); the first switching to our
+         * task, the second putting it to sleep.
+         */
+        smp_rmb();
+
+        /*
          * If the owning (remote) cpu is still in the middle of schedule() with
          * this task as prev, wait until its done referencing the task.
          */
         while (p->on_cpu)
                 cpu_relax();
         /*
-         * Pairs with the smp_wmb() in finish_lock_switch().
+         * Combined with the control dependency above, we have an effective
+         * smp_load_acquire() without the need for full barriers.
+         *
+         * Pairs with the smp_store_release() in finish_lock_switch().
+         *
+         * This ensures that tasks getting woken will be fully ordered against
+         * their previous state and preserve Program Order.
          */
         smp_rmb();
 
@@ -2039,7 +2064,6 @@ out:
  */
 int wake_up_process(struct task_struct *p)
 {
-        WARN_ON(task_is_stopped_or_traced(p));
         return try_to_wake_up(p, TASK_NORMAL, 0);
 }
 EXPORT_SYMBOL(wake_up_process);
@@ -5847,13 +5871,13 @@ static int init_rootdomain(struct root_domain *rd)
 {
         memset(rd, 0, sizeof(*rd));
 
-        if (!alloc_cpumask_var(&rd->span, GFP_KERNEL))
+        if (!zalloc_cpumask_var(&rd->span, GFP_KERNEL))
                 goto out;
-        if (!alloc_cpumask_var(&rd->online, GFP_KERNEL))
+        if (!zalloc_cpumask_var(&rd->online, GFP_KERNEL))
                 goto free_span;
-        if (!alloc_cpumask_var(&rd->dlo_mask, GFP_KERNEL))
+        if (!zalloc_cpumask_var(&rd->dlo_mask, GFP_KERNEL))
                 goto free_online;
-        if (!alloc_cpumask_var(&rd->rto_mask, GFP_KERNEL))
+        if (!zalloc_cpumask_var(&rd->rto_mask, GFP_KERNEL))
                 goto free_dlo_mask;
 
         init_dl_bw(&rd->dl_bw);
diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c
index 26a54461bf59..05de80b48586 100644
--- a/kernel/sched/cputime.c
+++ b/kernel/sched/cputime.c
@@ -788,6 +788,9 @@ cputime_t task_gtime(struct task_struct *t)
         unsigned int seq;
         cputime_t gtime;
 
+        if (!context_tracking_is_enabled())
+                return t->gtime;
+
         do {
                 seq = read_seqbegin(&t->vtime_seqlock);
 
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index e3cc16312046..8ec86abe0ea1 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -64,7 +64,7 @@ static void start_rt_bandwidth(struct rt_bandwidth *rt_b)
         raw_spin_unlock(&rt_b->rt_runtime_lock);
 }
 
-#ifdef CONFIG_SMP
+#if defined(CONFIG_SMP) && defined(HAVE_RT_PUSH_IPI)
 static void push_irq_work_func(struct irq_work *work);
 #endif
 
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index efd3bfc7e347..b242775bf670 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1073,6 +1073,9 @@ static inline void finish_lock_switch(struct rq *rq, struct task_struct *prev)
          * We must ensure this doesn't happen until the switch is completely
          * finished.
          *
+         * In particular, the load of prev->state in finish_task_switch() must
+         * happen before this.
+         *
          * Pairs with the control dependency and rmb in try_to_wake_up().
          */
         smp_store_release(&prev->on_cpu, 0);
diff --git a/kernel/sched/wait.c b/kernel/sched/wait.c
index 052e02672d12..f10bd873e684 100644
--- a/kernel/sched/wait.c
+++ b/kernel/sched/wait.c
@@ -583,18 +583,18 @@ EXPORT_SYMBOL(wake_up_atomic_t);
 
 __sched int bit_wait(struct wait_bit_key *word)
 {
-        if (signal_pending_state(current->state, current))
-                return 1;
         schedule();
+        if (signal_pending(current))
+                return -EINTR;
         return 0;
 }
 EXPORT_SYMBOL(bit_wait);
 
 __sched int bit_wait_io(struct wait_bit_key *word)
 {
-        if (signal_pending_state(current->state, current))
-                return 1;
         io_schedule();
+        if (signal_pending(current))
+                return -EINTR;
         return 0;
 }
 EXPORT_SYMBOL(bit_wait_io);
@@ -602,11 +602,11 @@ EXPORT_SYMBOL(bit_wait_io);
 __sched int bit_wait_timeout(struct wait_bit_key *word)
 {
         unsigned long now = READ_ONCE(jiffies);
-        if (signal_pending_state(current->state, current))
-                return 1;
         if (time_after_eq(now, word->timeout))
                 return -EAGAIN;
         schedule_timeout(word->timeout - now);
+        if (signal_pending(current))
+                return -EINTR;
         return 0;
 }
 EXPORT_SYMBOL_GPL(bit_wait_timeout);
@@ -614,11 +614,11 @@ EXPORT_SYMBOL_GPL(bit_wait_timeout);
 __sched int bit_wait_io_timeout(struct wait_bit_key *word)
 {
         unsigned long now = READ_ONCE(jiffies);
-        if (signal_pending_state(current->state, current))
-                return 1;
         if (time_after_eq(now, word->timeout))
                 return -EAGAIN;
         io_schedule_timeout(word->timeout - now);
+        if (signal_pending(current))
+                return -EINTR;
         return 0;
 }
 EXPORT_SYMBOL_GPL(bit_wait_io_timeout);