sched: Add TASK_ANY for wait_task_inactive()

Now that wait_task_inactive()'s @match_state argument is a mask (like
ttwu()) it is possible to replace the special !match_state case with
an 'all-states' value such that any blocked state will match.

Suggested-by: Ingo Molnar (mingo@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/YxhkzfuFTvRnpUaH@hirez.programming.kicks-ass.net

Author: Peter Zijlstra

drivers/powercap/idle_inject.c

@@ -254,7 +254,7 @@ void idle_inject_stop(struct idle_inject_device *ii_dev)
 		iit = per_cpu_ptr(&idle_inject_thread, cpu);
 		iit->should_run = 0;
 
-		wait_task_inactive(iit->tsk, 0);
+		wait_task_inactive(iit->tsk, TASK_ANY);
 	}
 
 	cpu_hotplug_enable();

fs/coredump.c

@@ -412,7 +412,7 @@ static int coredump_wait(int exit_code, struct core_state *core_state)
 		 */
 		ptr = core_state->dumper.next;
 		while (ptr != NULL) {
-			wait_task_inactive(ptr->task, 0);
+			wait_task_inactive(ptr->task, TASK_ANY);
 			ptr = ptr->next;
 		}
 	}

include/linux/sched.h

@@ -101,6 +101,8 @@ struct task_group;
 #define TASK_RTLOCK_WAIT		0x1000
 #define TASK_STATE_MAX			0x2000
 
+#define TASK_ANY			(TASK_STATE_MAX-1)
+
 /* Convenience macros for the sake of set_current_state: */
 #define TASK_KILLABLE			(TASK_WAKEKILL | TASK_UNINTERRUPTIBLE)
 #define TASK_STOPPED			(TASK_WAKEKILL | __TASK_STOPPED)

kernel/sched/core.c

@@ -3253,12 +3253,12 @@ int migrate_swap(struct task_struct *cur, struct task_struct *p,
 /*
  * wait_task_inactive - wait for a thread to unschedule.
  *
- * If @match_state is nonzero, it's the @p->state value just checked and
- * not expected to change.  If it changes, i.e. @p might have woken up,
- * then return zero.  When we succeed in waiting for @p to be off its CPU,
- * we return a positive number (its total switch count).  If a second call
- * a short while later returns the same number, the caller can be sure that
- * @p has remained unscheduled the whole time.
+ * Wait for the thread to block in any of the states set in @match_state.
+ * If it changes, i.e. @p might have woken up, then return zero.  When we
+ * succeed in waiting for @p to be off its CPU, we return a positive number
+ * (its total switch count).  If a second call a short while later returns the
+ * same number, the caller can be sure that @p has remained unscheduled the
+ * whole time.
  *
  * The caller must ensure that the task *will* unschedule sometime soon,
  * else this function might spin for a *long* time. This function can't
@@ -3294,7 +3294,7 @@ unsigned long wait_task_inactive(struct task_struct *p, unsigned int match_state
 		 * is actually now running somewhere else!
 		 */
 		while (task_on_cpu(rq, p)) {
-			if (match_state && !(READ_ONCE(p->__state) & match_state))
+			if (!(READ_ONCE(p->__state) & match_state))
 				return 0;
 			cpu_relax();
 		}
@@ -3309,7 +3309,7 @@ unsigned long wait_task_inactive(struct task_struct *p, unsigned int match_state
 		running = task_on_cpu(rq, p);
 		queued = task_on_rq_queued(p);
 		ncsw = 0;
-		if (!match_state || (READ_ONCE(p->__state) & match_state))
+		if (READ_ONCE(p->__state) & match_state)
 			ncsw = p->nvcsw | LONG_MIN; /* sets MSB */
 		task_rq_unlock(rq, p, &rf);