[PATCH 5/6] sched/proxy: Remove PROXY_WAKING

[Peter Zijlstra]

From: K Prateek Nayak <kprateek.nayak@xxxxxxx>

Now that the proxy path uses ->is_blocked, use the '->is_blocked &&
!->blocked_on' state instead of PROXY_WAKING. Notably, this is where a
blocked_on relation is broken but the donor task might still need a return
migration.

(Not-yet-)Signed-off-by: K Prateek Nayak <kprateek.nayak@xxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
---
 include/linux/sched.h     |   50 +---------------------------------------------
 kernel/locking/mutex.c    |    4 +--
 kernel/locking/ww_mutex.h |    4 +--
 kernel/sched/core.c       |   13 ++++++++++-
 4 files changed, 17 insertions(+), 54 deletions(-)

--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -2202,19 +2202,10 @@ extern int __cond_resched_rwlock_write(r
 
 #ifndef CONFIG_PREEMPT_RT
 
-/*
- * With proxy exec, if a task has been proxy-migrated, it may be a donor
- * on a cpu that it can't actually run on. Thus we need a special state
- * to denote that the task is being woken, but that it needs to be
- * evaluated for return-migration before it is run. So if the task is
- * blocked_on PROXY_WAKING, return migrate it before running it.
- */
-#define PROXY_WAKING ((struct mutex *)(-1L))
-
 static inline struct mutex *__get_task_blocked_on(struct task_struct *p)
 {
 	lockdep_assert_held_once(&p->blocked_lock);
-	return p->blocked_on == PROXY_WAKING ? NULL : p->blocked_on;
+	return p->blocked_on;
 }
 
 static inline void __set_task_blocked_on(struct task_struct *p, struct mutex *m)
@@ -2242,7 +2233,7 @@ static inline void __clear_task_blocked_
 	 * blocked_on relationships, but make sure we are not
 	 * clearing the relationship with a different lock.
 	 */
-	WARN_ON_ONCE(m && p->blocked_on && p->blocked_on != m && p->blocked_on != PROXY_WAKING);
+	WARN_ON_ONCE(m && p->blocked_on && p->blocked_on != m);
 	p->blocked_on = NULL;
 }
 
@@ -2251,35 +2242,6 @@ static inline void clear_task_blocked_on
 	guard(raw_spinlock_irqsave)(&p->blocked_lock);
 	__clear_task_blocked_on(p, m);
 }
-
-static inline void __set_task_blocked_on_waking(struct task_struct *p, struct mutex *m)
-{
-	/* Currently we serialize blocked_on under the task::blocked_lock */
-	lockdep_assert_held_once(&p->blocked_lock);
-
-	if (!sched_proxy_exec()) {
-		__clear_task_blocked_on(p, m);
-		return;
-	}
-
-	/* Don't set PROXY_WAKING if blocked_on was already cleared */
-	if (!p->blocked_on)
-		return;
-	/*
-	 * There may be cases where we set PROXY_WAKING on tasks that were
-	 * already set to waking, but make sure we are not changing
-	 * the relationship with a different lock.
-	 */
-	WARN_ON_ONCE(m && p->blocked_on != m && p->blocked_on != PROXY_WAKING);
-	p->blocked_on = PROXY_WAKING;
-}
-
-static inline void set_task_blocked_on_waking(struct task_struct *p, struct mutex *m)
-{
-	guard(raw_spinlock_irqsave)(&p->blocked_lock);
-	__set_task_blocked_on_waking(p, m);
-}
-
 #else
 static inline void __clear_task_blocked_on(struct task_struct *p, struct rt_mutex *m)
 {
@@ -2288,14 +2250,6 @@ static inline void __clear_task_blocked_
 static inline void clear_task_blocked_on(struct task_struct *p, struct rt_mutex *m)
 {
 }
-
-static inline void __set_task_blocked_on_waking(struct task_struct *p, struct rt_mutex *m)
-{
-}
-
-static inline void set_task_blocked_on_waking(struct task_struct *p, struct rt_mutex *m)
-{
-}
 #endif /* !CONFIG_PREEMPT_RT */
 
 static __always_inline bool need_resched(void)
--- a/kernel/locking/mutex.c
+++ b/kernel/locking/mutex.c
@@ -1043,7 +1043,7 @@ static noinline void __sched __mutex_unl
 			next_lock = __get_task_blocked_on(donor);
 			if (next_lock == lock) {
 				next = get_task_struct(donor);
-				__set_task_blocked_on_waking(donor, next_lock);
+				__clear_task_blocked_on(next, lock);
 				current->blocked_donor = NULL;
 			}
 			raw_spin_unlock(&donor->blocked_lock);
@@ -1059,7 +1059,7 @@ static noinline void __sched __mutex_unl
 
 		raw_spin_lock_nested(&next->blocked_lock, SINGLE_DEPTH_NESTING);
 		debug_mutex_wake_waiter(lock, waiter);
-		__set_task_blocked_on_waking(next, lock);
+		__clear_task_blocked_on(next, lock);
 		raw_spin_unlock(&next->blocked_lock);
 
 	}
--- a/kernel/locking/ww_mutex.h
+++ b/kernel/locking/ww_mutex.h
@@ -324,7 +324,7 @@ __ww_mutex_die(struct MUTEX *lock, struc
 		 * blocked_on to PROXY_WAKING. Otherwise we can see
 		 * circular blocked_on relationships that can't resolve.
 		 */
-		set_task_blocked_on_waking(waiter->task, lock);
+		clear_task_blocked_on(waiter->task, lock);
 		wake_q_add(wake_q, waiter->task);
 	}
 
@@ -383,7 +383,7 @@ static bool __ww_mutex_wound(struct MUTE
 			 * are waking the mutex owner, who may be currently
 			 * blocked on a different mutex.
 			 */
-			set_task_blocked_on_waking(owner, NULL);
+			clear_task_blocked_on(owner, NULL);
 			wake_q_add(wake_q, owner);
 		}
 		return true;
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -6856,7 +6865,7 @@ find_proxy_task(struct rq *rq, struct ta
 	for (p = donor; p->is_blocked; p = owner) {
 		/* if its PROXY_WAKING, do return migration or run if current */
 		struct mutex *mutex = p->blocked_on;
-		if (!mutex || mutex == PROXY_WAKING) {
+		if (!mutex) {
 			clear_task_blocked_on(p, mutex);
 			if (task_current(rq, p)) {
 				p->is_blocked = 0;