Merge branch 'x86-pti-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull x86/pti updates from Thomas Gleixner:
 "A mixed bag of fixes and updates for the ghosts which are hunting us.

  The scheduler fixes have been pulled into that branch to avoid
  conflicts.

   - A set of fixes to address a khread_parkme() race which caused lost
     wakeups and loss of state.

   - A deadlock fix for stop_machine() solved by moving the wakeups
     outside of the stopper_lock held region.

   - A set of Spectre V1 array access restrictions. The possible
     problematic spots were discuvered by Dan Carpenters new checks in
     smatch.

   - Removal of an unused file which was forgotten when the rest of that
     functionality was removed"

* 'x86-pti-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86/vdso: Remove unused file
  perf/x86/cstate: Fix possible Spectre-v1 indexing for pkg_msr
  perf/x86/msr: Fix possible Spectre-v1 indexing in the MSR driver
  perf/x86: Fix possible Spectre-v1 indexing for x86_pmu::event_map()
  perf/x86: Fix possible Spectre-v1 indexing for hw_perf_event cache_*
  perf/core: Fix possible Spectre-v1 indexing for ->aux_pages[]
  sched/autogroup: Fix possible Spectre-v1 indexing for sched_prio_to_weight[]
  sched/core: Fix possible Spectre-v1 indexing for sched_prio_to_weight[]
  sched/core: Introduce set_special_state()
  kthread, sched/wait: Fix kthread_parkme() completion issue
  kthread, sched/wait: Fix kthread_parkme() wait-loop
  sched/fair: Fix the update of blocked load when newly idle
  stop_machine, sched: Fix migrate_swap() vs. active_balance() deadlock

3 files changed, 47 insertions, 6 deletions

diff --git a/include/linux/kthread.h b/include/linux/kthread.h
index c1961761311d..2803264c512f 100644
--- a/include/linux/kthread.h
+++ b/include/linux/kthread.h
@@ -62,6 +62,7 @@ void *kthread_probe_data(struct task_struct *k);
 int kthread_park(struct task_struct *k);
 void kthread_unpark(struct task_struct *k);
 void kthread_parkme(void);
+void kthread_park_complete(struct task_struct *k);
 
 int kthreadd(void *unused);
 extern struct task_struct *kthreadd_task;
diff --git a/include/linux/sched.h b/include/linux/sched.h
index b3d697f3b573..c2413703f45d 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -112,17 +112,36 @@ struct task_group;
 
 #ifdef CONFIG_DEBUG_ATOMIC_SLEEP
 
+/*
+ * Special states are those that do not use the normal wait-loop pattern. See
+ * the comment with set_special_state().
+ */
+#define is_special_task_state(state)				\
+	((state) & (__TASK_STOPPED | __TASK_TRACED | TASK_DEAD))
+
 #define __set_current_state(state_value)			\
 	do {							\
+		WARN_ON_ONCE(is_special_task_state(state_value));\
 		current->task_state_change = _THIS_IP_;		\
 		current->state = (state_value);			\
 	} while (0)
+
 #define set_current_state(state_value)				\
 	do {							\
+		WARN_ON_ONCE(is_special_task_state(state_value));\
 		current->task_state_change = _THIS_IP_;		\
 		smp_store_mb(current->state, (state_value));	\
 	} while (0)
 
+#define set_special_state(state_value)					\
+	do {								\
+		unsigned long flags; /* may shadow */			\
+		WARN_ON_ONCE(!is_special_task_state(state_value));	\
+		raw_spin_lock_irqsave(&current->pi_lock, flags);	\
+		current->task_state_change = _THIS_IP_;			\
+		current->state = (state_value);				\
+		raw_spin_unlock_irqrestore(&current->pi_lock, flags);	\
+	} while (0)
 #else
 /*
  * set_current_state() includes a barrier so that the write of current->state
@@ -144,8 +163,8 @@ struct task_group;
  *
  * The above is typically ordered against the wakeup, which does:
  *
- *	need_sleep = false;
- *	wake_up_state(p, TASK_UNINTERRUPTIBLE);
+ *   need_sleep = false;
+ *   wake_up_state(p, TASK_UNINTERRUPTIBLE);
  *
  * Where wake_up_state() (and all other wakeup primitives) imply enough
  * barriers to order the store of the variable against wakeup.
@@ -154,12 +173,33 @@ struct task_group;
  * once it observes the TASK_UNINTERRUPTIBLE store the waking CPU can issue a
  * TASK_RUNNING store which can collide with __set_current_state(TASK_RUNNING).
  *
- * This is obviously fine, since they both store the exact same value.
+ * However, with slightly different timing the wakeup TASK_RUNNING store can
+ * also collide with the TASK_UNINTERRUPTIBLE store. Loosing that store is not
+ * a problem either because that will result in one extra go around the loop
+ * and our @cond test will save the day.
  *
  * Also see the comments of try_to_wake_up().
  */
-#define __set_current_state(state_value) do { current->state = (state_value); } while (0)
-#define set_current_state(state_value)	 smp_store_mb(current->state, (state_value))
+#define __set_current_state(state_value)				\
+	current->state = (state_value)
+
+#define set_current_state(state_value)					\
+	smp_store_mb(current->state, (state_value))
+
+/*
+ * set_special_state() should be used for those states when the blocking task
+ * can not use the regular condition based wait-loop. In that case we must
+ * serialize against wakeups such that any possible in-flight TASK_RUNNING stores
+ * will not collide with our state change.
+ */
+#define set_special_state(state_value)					\
+	do {								\
+		unsigned long flags; /* may shadow */			\
+		raw_spin_lock_irqsave(&current->pi_lock, flags);	\
+		current->state = (state_value);				\
+		raw_spin_unlock_irqrestore(&current->pi_lock, flags);	\
+	} while (0)
+
 #endif
 
 /* Task command name length: */
diff --git a/include/linux/sched/signal.h b/include/linux/sched/signal.h
index a7ce74c74e49..113d1ad1ced7 100644
--- a/include/linux/sched/signal.h
+++ b/include/linux/sched/signal.h
@@ -280,7 +280,7 @@ static inline void kernel_signal_stop(void)
 {
 	spin_lock_irq(&current->sighand->siglock);
 	if (current->jobctl & JOBCTL_STOP_DEQUEUED)
-		__set_current_state(TASK_STOPPED);
+		set_special_state(TASK_STOPPED);
 	spin_unlock_irq(&current->sighand->siglock);
 
 	schedule();