sched/psi: Use task->psi_flags to clear in CPU migration

The commit d583d36 ("psi: Fix psi state corruption when schedule()
races with cgroup move") fixed a race problem by making cgroup_move_task()
use task->psi_flags instead of looking at the scheduler state.

We can extend task->psi_flags usage to CPU migration, which should be
a minor optimization for performance and code simplicity.

Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Link: https://lore.kernel.org/r/20220926081931.45420-1-zhouchengming@bytedance.com

Author: Chengming Zhou

include/linux/sched.h

@@ -888,9 +888,6 @@ struct task_struct {
 	unsigned			sched_reset_on_fork:1;
 	unsigned			sched_contributes_to_load:1;
 	unsigned			sched_migrated:1;
-#ifdef CONFIG_PSI
-	unsigned			sched_psi_wake_requeue:1;
-#endif
 
 	/* Force alignment to the next boundary: */
 	unsigned			:0;

kernel/sched/core.c

@@ -2053,7 +2053,7 @@ static inline void enqueue_task(struct rq *rq, struct task_struct *p, int flags)
 
 	if (!(flags & ENQUEUE_RESTORE)) {
 		sched_info_enqueue(rq, p);
-		psi_enqueue(p, flags & ENQUEUE_WAKEUP);
+		psi_enqueue(p, (flags & ENQUEUE_WAKEUP) && !(flags & ENQUEUE_MIGRATED));
 	}
 
 	uclamp_rq_inc(rq, p);

kernel/sched/stats.h

@@ -128,11 +128,9 @@ static inline void psi_enqueue(struct task_struct *p, bool wakeup)
 	if (p->in_memstall)
 		set |= TSK_MEMSTALL_RUNNING;
 
-	if (!wakeup || p->sched_psi_wake_requeue) {
+	if (!wakeup) {
 		if (p->in_memstall)
 			set |= TSK_MEMSTALL;
-		if (p->sched_psi_wake_requeue)
-			p->sched_psi_wake_requeue = 0;
 	} else {
 		if (p->in_iowait)
 			clear |= TSK_IOWAIT;
@@ -143,8 +141,6 @@ static inline void psi_enqueue(struct task_struct *p, bool wakeup)
 
 static inline void psi_dequeue(struct task_struct *p, bool sleep)
 {
-	int clear = TSK_RUNNING;
-
 	if (static_branch_likely(&psi_disabled))
 		return;
 
@@ -157,10 +153,7 @@ static inline void psi_dequeue(struct task_struct *p, bool sleep)
 	if (sleep)
 		return;
 
-	if (p->in_memstall)
-		clear |= (TSK_MEMSTALL | TSK_MEMSTALL_RUNNING);
-
-	psi_task_change(p, clear, 0);
+	psi_task_change(p, p->psi_flags, 0);
 }
 
 static inline void psi_ttwu_dequeue(struct task_struct *p)
@@ -172,19 +165,12 @@ static inline void psi_ttwu_dequeue(struct task_struct *p)
 	 * deregister its sleep-persistent psi states from the old
 	 * queue, and let psi_enqueue() know it has to requeue.
 	 */
-	if (unlikely(p->in_iowait || p->in_memstall)) {
+	if (unlikely(p->psi_flags)) {
 		struct rq_flags rf;
 		struct rq *rq;
-		int clear = 0;
-
-		if (p->in_iowait)
-			clear |= TSK_IOWAIT;
-		if (p->in_memstall)
-			clear |= TSK_MEMSTALL;
 
 		rq = __task_rq_lock(p, &rf);
-		psi_task_change(p, clear, 0);
-		p->sched_psi_wake_requeue = 1;
+		psi_task_change(p, p->psi_flags, 0);
 		__task_rq_unlock(rq, &rf);
 	}
 }