[RESEND][PATCH v9 0/7] Preparatory changes for Proxy Execution v9

[RESEND][PATCH v9 0/7] Preparatory changes for Proxy Execution v9

[John Stultz]

After sending out v7 of Proxy Execution, I got feedback that the
patch series was getting a bit unwieldy to review, and Qais
suggested I break out just the cleanups/preparatory components
of the patch series and submit them on their own in the hope we
can start to merge the less complex bits and discussion can
focus on the more complicated portions afterwards.

So for both the v8 & v9 of this series, I only submitted those
earlier cleanup/preparatory changes (note, between v8 and v9
there were no changes to these preparatory changes):
  https://lore.kernel.org/lkml/20240210002328.4126422-1-jstultz@google.com/
  https://lore.kernel.org/lkml/20240315044007.2778856-1-jstultz@google.com/

After sending v9 out a few weeks back, I’ve not heard too much,
so I wanted to resend this again.

(The only changes here are that I've added the Tested-by: and
Acked-by tags I received & rebased to 6.9-rc2).

As before, If you are interested, the full v9 series, it can be
found here:
  https://github.com/johnstultz-work/linux-dev/commits/proxy-exec-v9-6.9-rc2
  https://github.com/johnstultz-work/linux-dev.git proxy-exec-v9-6.9-rc2

Review and feedback would be greatly appreciated!

Thanks so much!
-john

Cc: Joel Fernandes <joelaf@google.com>
Cc: Qais Yousef <qyousef@google.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Valentin Schneider <vschneid@redhat.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Ben Segall <bsegall@google.com>
Cc: Zimuzo Ezeozue <zezeozue@google.com>
Cc: Youssef Esmat <youssefesmat@google.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Daniel Bristot de Oliveira <bristot@redhat.com>
Cc: Will Deacon <will@kernel.org>
Cc: Waiman Long <longman@redhat.com>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Metin Kaya <Metin.Kaya@arm.com>
Cc: Xuewen Yan <xuewen.yan94@gmail.com>
Cc: K Prateek Nayak <kprateek.nayak@amd.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: kernel-team@android.com

Connor O'Brien (2):
  sched: Add do_push_task helper
  sched: Consolidate pick_*_task to task_is_pushable helper

John Stultz (1):
  sched: Split out __schedule() deactivate task logic into a helper

Juri Lelli (2):
  locking/mutex: Make mutex::wait_lock irq safe
  locking/mutex: Expose __mutex_owner()

Peter Zijlstra (2):
  locking/mutex: Remove wakeups from under mutex::wait_lock
  sched: Split scheduler and execution contexts

 kernel/locking/mutex.c       |  60 +++++++----------
 kernel/locking/mutex.h       |  25 +++++++
 kernel/locking/rtmutex.c     |  26 +++++---
 kernel/locking/rwbase_rt.c   |   4 +-
 kernel/locking/rwsem.c       |   4 +-
 kernel/locking/spinlock_rt.c |   3 +-
 kernel/locking/ww_mutex.h    |  49 ++++++++------
 kernel/sched/core.c          | 122 +++++++++++++++++++++--------------
 kernel/sched/deadline.c      |  53 ++++++---------
 kernel/sched/fair.c          |  18 +++---
 kernel/sched/rt.c            |  59 +++++++----------
 kernel/sched/sched.h         |  44 ++++++++++++-
 12 files changed, 268 insertions(+), 199 deletions(-)

-- 
2.44.0.478.gd926399ef9-goog

[RESEND][PATCH v9 1/7] locking/mutex: Remove wakeups from under mutex::wait_lock

[John Stultz]

From: Peter Zijlstra <peterz@infradead.org>

In preparation to nest mutex::wait_lock under rq::lock we need to remove
wakeups from under it.

Cc: Joel Fernandes <joelaf@google.com>
Cc: Qais Yousef <qyousef@google.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Valentin Schneider <vschneid@redhat.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Ben Segall <bsegall@google.com>
Cc: Zimuzo Ezeozue <zezeozue@google.com>
Cc: Youssef Esmat <youssefesmat@google.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Daniel Bristot de Oliveira <bristot@redhat.com>
Cc: Will Deacon <will@kernel.org>
Cc: Waiman Long <longman@redhat.com>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Metin Kaya <Metin.Kaya@arm.com>
Cc: Xuewen Yan <xuewen.yan94@gmail.com>
Cc: K Prateek Nayak <kprateek.nayak@amd.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: kernel-team@android.com
Tested-by: K Prateek Nayak <kprateek.nayak@amd.com>
Acked-by: Davidlohr Bueso <dave@stgolabs.net>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
[Heavily changed after 55f036ca7e74 ("locking: WW mutex cleanup") and
08295b3b5bee ("locking: Implement an algorithm choice for Wound-Wait
mutexes")]
Signed-off-by: Juri Lelli <juri.lelli@redhat.com>
[jstultz: rebased to mainline, added extra wake_up_q & init
 to avoid hangs, similar to Connor's rework of this patch]
Signed-off-by: John Stultz <jstultz@google.com>
---
v5:
* Reverted back to an earlier version of this patch to undo
  the change that kept the wake_q in the ctx structure, as
  that broke the rule that the wake_q must always be on the
  stack, as its not safe for concurrency.
v6:
* Made tweaks suggested by Waiman Long
v7:
* Fixups to pass wake_qs down for PREEMPT_RT logic
---
 kernel/locking/mutex.c       | 17 +++++++++++++----
 kernel/locking/rtmutex.c     | 26 +++++++++++++++++---------
 kernel/locking/rwbase_rt.c   |  4 +++-
 kernel/locking/rwsem.c       |  4 ++--
 kernel/locking/spinlock_rt.c |  3 ++-
 kernel/locking/ww_mutex.h    | 29 ++++++++++++++++++-----------
 6 files changed, 55 insertions(+), 28 deletions(-)

diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c
index cbae8c0b89ab..980ce630232c 100644
--- a/kernel/locking/mutex.c
+++ b/kernel/locking/mutex.c
@@ -575,6 +575,7 @@ __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclas
 		    struct lockdep_map *nest_lock, unsigned long ip,
 		    struct ww_acquire_ctx *ww_ctx, const bool use_ww_ctx)
 {
+	DEFINE_WAKE_Q(wake_q);
 	struct mutex_waiter waiter;
 	struct ww_mutex *ww;
 	int ret;
@@ -625,7 +626,7 @@ __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclas
 	 */
 	if (__mutex_trylock(lock)) {
 		if (ww_ctx)
-			__ww_mutex_check_waiters(lock, ww_ctx);
+			__ww_mutex_check_waiters(lock, ww_ctx, &wake_q);
 
 		goto skip_wait;
 	}
@@ -645,7 +646,7 @@ __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclas
 		 * Add in stamp order, waking up waiters that must kill
 		 * themselves.
 		 */
-		ret = __ww_mutex_add_waiter(&waiter, lock, ww_ctx);
+		ret = __ww_mutex_add_waiter(&waiter, lock, ww_ctx, &wake_q);
 		if (ret)
 			goto err_early_kill;
 	}
@@ -681,6 +682,11 @@ __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclas
 		}
 
 		raw_spin_unlock(&lock->wait_lock);
+		/* Make sure we do wakeups before calling schedule */
+		if (!wake_q_empty(&wake_q)) {
+			wake_up_q(&wake_q);
+			wake_q_init(&wake_q);
+		}
 		schedule_preempt_disabled();
 
 		first = __mutex_waiter_is_first(lock, &waiter);
@@ -714,7 +720,7 @@ __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclas
 		 */
 		if (!ww_ctx->is_wait_die &&
 		    !__mutex_waiter_is_first(lock, &waiter))
-			__ww_mutex_check_waiters(lock, ww_ctx);
+			__ww_mutex_check_waiters(lock, ww_ctx, &wake_q);
 	}
 
 	__mutex_remove_waiter(lock, &waiter);
@@ -730,6 +736,7 @@ __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclas
 		ww_mutex_lock_acquired(ww, ww_ctx);
 
 	raw_spin_unlock(&lock->wait_lock);
+	wake_up_q(&wake_q);
 	preempt_enable();
 	return 0;
 
@@ -741,6 +748,7 @@ __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclas
 	raw_spin_unlock(&lock->wait_lock);
 	debug_mutex_free_waiter(&waiter);
 	mutex_release(&lock->dep_map, ip);
+	wake_up_q(&wake_q);
 	preempt_enable();
 	return ret;
 }
@@ -934,6 +942,7 @@ static noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigne
 		}
 	}
 
+	preempt_disable();
 	raw_spin_lock(&lock->wait_lock);
 	debug_mutex_unlock(lock);
 	if (!list_empty(&lock->wait_list)) {
@@ -952,8 +961,8 @@ static noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigne
 		__mutex_handoff(lock, next);
 
 	raw_spin_unlock(&lock->wait_lock);
-
 	wake_up_q(&wake_q);
+	preempt_enable();
 }
 
 #ifndef CONFIG_DEBUG_LOCK_ALLOC
diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
index 88d08eeb8bc0..59f17e7ccf89 100644
--- a/kernel/locking/rtmutex.c
+++ b/kernel/locking/rtmutex.c
@@ -34,13 +34,15 @@
 
 static inline int __ww_mutex_add_waiter(struct rt_mutex_waiter *waiter,
 					struct rt_mutex *lock,
-					struct ww_acquire_ctx *ww_ctx)
+					struct ww_acquire_ctx *ww_ctx,
+					struct wake_q_head *wake_q)
 {
 	return 0;
 }
 
 static inline void __ww_mutex_check_waiters(struct rt_mutex *lock,
-					    struct ww_acquire_ctx *ww_ctx)
+					    struct ww_acquire_ctx *ww_ctx,
+					    struct wake_q_head *wake_q)
 {
 }
 
@@ -1207,6 +1209,7 @@ static int __sched task_blocks_on_rt_mutex(struct rt_mutex_base *lock,
 	struct rt_mutex_waiter *top_waiter = waiter;
 	struct rt_mutex_base *next_lock;
 	int chain_walk = 0, res;
+	DEFINE_WAKE_Q(wake_q);
 
 	lockdep_assert_held(&lock->wait_lock);
 
@@ -1245,7 +1248,8 @@ static int __sched task_blocks_on_rt_mutex(struct rt_mutex_base *lock,
 
 		/* Check whether the waiter should back out immediately */
 		rtm = container_of(lock, struct rt_mutex, rtmutex);
-		res = __ww_mutex_add_waiter(waiter, rtm, ww_ctx);
+		res = __ww_mutex_add_waiter(waiter, rtm, ww_ctx, &wake_q);
+		wake_up_q(&wake_q);
 		if (res) {
 			raw_spin_lock(&task->pi_lock);
 			rt_mutex_dequeue(lock, waiter);
@@ -1678,7 +1682,8 @@ static int __sched __rt_mutex_slowlock(struct rt_mutex_base *lock,
 				       struct ww_acquire_ctx *ww_ctx,
 				       unsigned int state,
 				       enum rtmutex_chainwalk chwalk,
-				       struct rt_mutex_waiter *waiter)
+				       struct rt_mutex_waiter *waiter,
+				       struct wake_q_head *wake_q)
 {
 	struct rt_mutex *rtm = container_of(lock, struct rt_mutex, rtmutex);
 	struct ww_mutex *ww = ww_container_of(rtm);
@@ -1689,7 +1694,7 @@ static int __sched __rt_mutex_slowlock(struct rt_mutex_base *lock,
 	/* Try to acquire the lock again: */
 	if (try_to_take_rt_mutex(lock, current, NULL)) {
 		if (build_ww_mutex() && ww_ctx) {
-			__ww_mutex_check_waiters(rtm, ww_ctx);
+			__ww_mutex_check_waiters(rtm, ww_ctx, wake_q);
 			ww_mutex_lock_acquired(ww, ww_ctx);
 		}
 		return 0;
@@ -1707,7 +1712,7 @@ static int __sched __rt_mutex_slowlock(struct rt_mutex_base *lock,
 		/* acquired the lock */
 		if (build_ww_mutex() && ww_ctx) {
 			if (!ww_ctx->is_wait_die)
-				__ww_mutex_check_waiters(rtm, ww_ctx);
+				__ww_mutex_check_waiters(rtm, ww_ctx, wake_q);
 			ww_mutex_lock_acquired(ww, ww_ctx);
 		}
 	} else {
@@ -1729,7 +1734,8 @@ static int __sched __rt_mutex_slowlock(struct rt_mutex_base *lock,
 
 static inline int __rt_mutex_slowlock_locked(struct rt_mutex_base *lock,
 					     struct ww_acquire_ctx *ww_ctx,
-					     unsigned int state)
+					     unsigned int state,
+					     struct wake_q_head *wake_q)
 {
 	struct rt_mutex_waiter waiter;
 	int ret;
@@ -1738,7 +1744,7 @@ static inline int __rt_mutex_slowlock_locked(struct rt_mutex_base *lock,
 	waiter.ww_ctx = ww_ctx;
 
 	ret = __rt_mutex_slowlock(lock, ww_ctx, state, RT_MUTEX_MIN_CHAINWALK,
-				  &waiter);
+				  &waiter, wake_q);
 
 	debug_rt_mutex_free_waiter(&waiter);
 	return ret;
@@ -1754,6 +1760,7 @@ static int __sched rt_mutex_slowlock(struct rt_mutex_base *lock,
 				     struct ww_acquire_ctx *ww_ctx,
 				     unsigned int state)
 {
+	DEFINE_WAKE_Q(wake_q);
 	unsigned long flags;
 	int ret;
 
@@ -1775,8 +1782,9 @@ static int __sched rt_mutex_slowlock(struct rt_mutex_base *lock,
 	 * irqsave/restore variants.
 	 */
 	raw_spin_lock_irqsave(&lock->wait_lock, flags);
-	ret = __rt_mutex_slowlock_locked(lock, ww_ctx, state);
+	ret = __rt_mutex_slowlock_locked(lock, ww_ctx, state, &wake_q);
 	raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
+	wake_up_q(&wake_q);
 	rt_mutex_post_schedule();
 
 	return ret;
diff --git a/kernel/locking/rwbase_rt.c b/kernel/locking/rwbase_rt.c
index 34a59569db6b..e9d2f38b70f3 100644
--- a/kernel/locking/rwbase_rt.c
+++ b/kernel/locking/rwbase_rt.c
@@ -69,6 +69,7 @@ static int __sched __rwbase_read_lock(struct rwbase_rt *rwb,
 				      unsigned int state)
 {
 	struct rt_mutex_base *rtm = &rwb->rtmutex;
+	DEFINE_WAKE_Q(wake_q);
 	int ret;
 
 	rwbase_pre_schedule();
@@ -110,7 +111,7 @@ static int __sched __rwbase_read_lock(struct rwbase_rt *rwb,
 	 * For rwlocks this returns 0 unconditionally, so the below
 	 * !ret conditionals are optimized out.
 	 */
-	ret = rwbase_rtmutex_slowlock_locked(rtm, state);
+	ret = rwbase_rtmutex_slowlock_locked(rtm, state, &wake_q);
 
 	/*
 	 * On success the rtmutex is held, so there can't be a writer
@@ -122,6 +123,7 @@ static int __sched __rwbase_read_lock(struct rwbase_rt *rwb,
 	if (!ret)
 		atomic_inc(&rwb->readers);
 	raw_spin_unlock_irq(&rtm->wait_lock);
+	wake_up_q(&wake_q);
 	if (!ret)
 		rwbase_rtmutex_unlock(rtm);
 
diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c
index c6d17aee4209..79ab7b8df5c1 100644
--- a/kernel/locking/rwsem.c
+++ b/kernel/locking/rwsem.c
@@ -1415,8 +1415,8 @@ static inline void __downgrade_write(struct rw_semaphore *sem)
 #define rwbase_rtmutex_lock_state(rtm, state)		\
 	__rt_mutex_lock(rtm, state)
 
-#define rwbase_rtmutex_slowlock_locked(rtm, state)	\
-	__rt_mutex_slowlock_locked(rtm, NULL, state)
+#define rwbase_rtmutex_slowlock_locked(rtm, state, wq)	\
+	__rt_mutex_slowlock_locked(rtm, NULL, state, wq)
 
 #define rwbase_rtmutex_unlock(rtm)			\
 	__rt_mutex_unlock(rtm)
diff --git a/kernel/locking/spinlock_rt.c b/kernel/locking/spinlock_rt.c
index 38e292454fcc..fb1810a14c9d 100644
--- a/kernel/locking/spinlock_rt.c
+++ b/kernel/locking/spinlock_rt.c
@@ -162,7 +162,8 @@ rwbase_rtmutex_lock_state(struct rt_mutex_base *rtm, unsigned int state)
 }
 
 static __always_inline int
-rwbase_rtmutex_slowlock_locked(struct rt_mutex_base *rtm, unsigned int state)
+rwbase_rtmutex_slowlock_locked(struct rt_mutex_base *rtm, unsigned int state,
+			       struct wake_q_head *wake_q)
 {
 	rtlock_slowlock_locked(rtm);
 	return 0;
diff --git a/kernel/locking/ww_mutex.h b/kernel/locking/ww_mutex.h
index 3ad2cc4823e5..7189c6631d90 100644
--- a/kernel/locking/ww_mutex.h
+++ b/kernel/locking/ww_mutex.h
@@ -275,7 +275,7 @@ __ww_ctx_less(struct ww_acquire_ctx *a, struct ww_acquire_ctx *b)
  */
 static bool
 __ww_mutex_die(struct MUTEX *lock, struct MUTEX_WAITER *waiter,
-	       struct ww_acquire_ctx *ww_ctx)
+	       struct ww_acquire_ctx *ww_ctx, struct wake_q_head *wake_q)
 {
 	if (!ww_ctx->is_wait_die)
 		return false;
@@ -284,7 +284,7 @@ __ww_mutex_die(struct MUTEX *lock, struct MUTEX_WAITER *waiter,
 #ifndef WW_RT
 		debug_mutex_wake_waiter(lock, waiter);
 #endif
-		wake_up_process(waiter->task);
+		wake_q_add(wake_q, waiter->task);
 	}
 
 	return true;
@@ -299,7 +299,8 @@ __ww_mutex_die(struct MUTEX *lock, struct MUTEX_WAITER *waiter,
  */
 static bool __ww_mutex_wound(struct MUTEX *lock,
 			     struct ww_acquire_ctx *ww_ctx,
-			     struct ww_acquire_ctx *hold_ctx)
+			     struct ww_acquire_ctx *hold_ctx,
+			     struct wake_q_head *wake_q)
 {
 	struct task_struct *owner = __ww_mutex_owner(lock);
 
@@ -331,7 +332,7 @@ static bool __ww_mutex_wound(struct MUTEX *lock,
 		 * wakeup pending to re-read the wounded state.
 		 */
 		if (owner != current)
-			wake_up_process(owner);
+			wake_q_add(wake_q, owner);
 
 		return true;
 	}
@@ -352,7 +353,8 @@ static bool __ww_mutex_wound(struct MUTEX *lock,
  * The current task must not be on the wait list.
  */
 static void
-__ww_mutex_check_waiters(struct MUTEX *lock, struct ww_acquire_ctx *ww_ctx)
+__ww_mutex_check_waiters(struct MUTEX *lock, struct ww_acquire_ctx *ww_ctx,
+			 struct wake_q_head *wake_q)
 {
 	struct MUTEX_WAITER *cur;
 
@@ -364,8 +366,8 @@ __ww_mutex_check_waiters(struct MUTEX *lock, struct ww_acquire_ctx *ww_ctx)
 		if (!cur->ww_ctx)
 			continue;
 
-		if (__ww_mutex_die(lock, cur, ww_ctx) ||
-		    __ww_mutex_wound(lock, cur->ww_ctx, ww_ctx))
+		if (__ww_mutex_die(lock, cur, ww_ctx, wake_q) ||
+		    __ww_mutex_wound(lock, cur->ww_ctx, ww_ctx, wake_q))
 			break;
 	}
 }
@@ -377,6 +379,8 @@ __ww_mutex_check_waiters(struct MUTEX *lock, struct ww_acquire_ctx *ww_ctx)
 static __always_inline void
 ww_mutex_set_context_fastpath(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
 {
+	DEFINE_WAKE_Q(wake_q);
+
 	ww_mutex_lock_acquired(lock, ctx);
 
 	/*
@@ -405,8 +409,10 @@ ww_mutex_set_context_fastpath(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
 	 * die or wound us.
 	 */
 	lock_wait_lock(&lock->base);
-	__ww_mutex_check_waiters(&lock->base, ctx);
+	__ww_mutex_check_waiters(&lock->base, ctx, &wake_q);
 	unlock_wait_lock(&lock->base);
+
+	wake_up_q(&wake_q);
 }
 
 static __always_inline int
@@ -488,7 +494,8 @@ __ww_mutex_check_kill(struct MUTEX *lock, struct MUTEX_WAITER *waiter,
 static inline int
 __ww_mutex_add_waiter(struct MUTEX_WAITER *waiter,
 		      struct MUTEX *lock,
-		      struct ww_acquire_ctx *ww_ctx)
+		      struct ww_acquire_ctx *ww_ctx,
+		      struct wake_q_head *wake_q)
 {
 	struct MUTEX_WAITER *cur, *pos = NULL;
 	bool is_wait_die;
@@ -532,7 +539,7 @@ __ww_mutex_add_waiter(struct MUTEX_WAITER *waiter,
 		pos = cur;
 
 		/* Wait-Die: ensure younger waiters die. */
-		__ww_mutex_die(lock, cur, ww_ctx);
+		__ww_mutex_die(lock, cur, ww_ctx, wake_q);
 	}
 
 	__ww_waiter_add(lock, waiter, pos);
@@ -550,7 +557,7 @@ __ww_mutex_add_waiter(struct MUTEX_WAITER *waiter,
 		 * such that either we or the fastpath will wound @ww->ctx.
 		 */
 		smp_mb();
-		__ww_mutex_wound(lock, ww_ctx, ww->ctx);
+		__ww_mutex_wound(lock, ww_ctx, ww->ctx, wake_q);
 	}
 
 	return 0;
-- 
2.44.0.478.gd926399ef9-goog

Re: [RESEND][PATCH v9 1/7] locking/mutex: Remove wakeups from under mutex::wait_lock

[Valentin Schneider]

On 01/04/24 16:44, John Stultz wrote:
> From: Peter Zijlstra <peterz@infradead.org>
>
> In preparation to nest mutex::wait_lock under rq::lock we need to remove
> wakeups from under it.
>
> Cc: Joel Fernandes <joelaf@google.com>
> Cc: Qais Yousef <qyousef@google.com>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Juri Lelli <juri.lelli@redhat.com>
> Cc: Vincent Guittot <vincent.guittot@linaro.org>
> Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
> Cc: Valentin Schneider <vschneid@redhat.com>
> Cc: Steven Rostedt <rostedt@goodmis.org>
> Cc: Ben Segall <bsegall@google.com>
> Cc: Zimuzo Ezeozue <zezeozue@google.com>
> Cc: Youssef Esmat <youssefesmat@google.com>
> Cc: Mel Gorman <mgorman@suse.de>
> Cc: Daniel Bristot de Oliveira <bristot@redhat.com>
> Cc: Will Deacon <will@kernel.org>
> Cc: Waiman Long <longman@redhat.com>
> Cc: Boqun Feng <boqun.feng@gmail.com>
> Cc: "Paul E. McKenney" <paulmck@kernel.org>
> Cc: Metin Kaya <Metin.Kaya@arm.com>
> Cc: Xuewen Yan <xuewen.yan94@gmail.com>
> Cc: K Prateek Nayak <kprateek.nayak@amd.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: kernel-team@android.com
> Tested-by: K Prateek Nayak <kprateek.nayak@amd.com>
> Acked-by: Davidlohr Bueso <dave@stgolabs.net>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> [Heavily changed after 55f036ca7e74 ("locking: WW mutex cleanup") and
> 08295b3b5bee ("locking: Implement an algorithm choice for Wound-Wait
> mutexes")]
> Signed-off-by: Juri Lelli <juri.lelli@redhat.com>
> [jstultz: rebased to mainline, added extra wake_up_q & init
>  to avoid hangs, similar to Connor's rework of this patch]
> Signed-off-by: John Stultz <jstultz@google.com>

This looks mostly good to me, some preemption questions below.

> @@ -934,6 +942,7 @@ static noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigne
>  		}
>  	}
>  
> +	preempt_disable();
>  	raw_spin_lock(&lock->wait_lock);
>  	debug_mutex_unlock(lock);
>  	if (!list_empty(&lock->wait_list)) {
> @@ -952,8 +961,8 @@ static noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigne
>  		__mutex_handoff(lock, next);
>

(minor nit) Could the preempt_disable() be moved here instead? IMO if it's
closer to the unlock it makes it clearer why it is there
(e.g. sched/core.c::affine_move_task(), rt_mutex_setprio(), __sched_setscheduler().

>  	raw_spin_unlock(&lock->wait_lock);
> -
>  	wake_up_q(&wake_q);
> +	preempt_enable();
>  }
>  

> @@ -1775,8 +1782,9 @@ static int __sched rt_mutex_slowlock(struct rt_mutex_base *lock,
>  	 * irqsave/restore variants.
>  	 */
>  	raw_spin_lock_irqsave(&lock->wait_lock, flags);
> -	ret = __rt_mutex_slowlock_locked(lock, ww_ctx, state);
> +	ret = __rt_mutex_slowlock_locked(lock, ww_ctx, state, &wake_q);
>  	raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
> +	wake_up_q(&wake_q);

Shouldn't this also be wrapped in a preempt-disabled region?

>  	rt_mutex_post_schedule();
>  
>  	return ret;

> @@ -122,6 +123,7 @@ static int __sched __rwbase_read_lock(struct rwbase_rt *rwb,
>  	if (!ret)
>  		atomic_inc(&rwb->readers);
>  	raw_spin_unlock_irq(&rtm->wait_lock);
> +	wake_up_q(&wake_q);

Same question wrt preemption.

>  	if (!ret)
>  		rwbase_rtmutex_unlock(rtm);
>  

Re: [RESEND][PATCH v9 1/7] locking/mutex: Remove wakeups from under mutex::wait_lock

[John Stultz]

On Tue, Apr 9, 2024 at 9:12 AM Valentin Schneider <vschneid@redhat.com> wrote:
> On 01/04/24 16:44, John Stultz wrote:
> > @@ -934,6 +942,7 @@ static noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigne
> >               }
> >       }
> >
> > +     preempt_disable();
> >       raw_spin_lock(&lock->wait_lock);
> >       debug_mutex_unlock(lock);
> >       if (!list_empty(&lock->wait_list)) {
> > @@ -952,8 +961,8 @@ static noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigne
> >               __mutex_handoff(lock, next);
> >
>
> (minor nit) Could the preempt_disable() be moved here instead? IMO if it's
> closer to the unlock it makes it clearer why it is there
> (e.g. sched/core.c::affine_move_task(), rt_mutex_setprio(), __sched_setscheduler().
>
> >       raw_spin_unlock(&lock->wait_lock);
> > -
> >       wake_up_q(&wake_q);
> > +     preempt_enable();
> >  }

Heh. Comically, that's how it started, but I was earlier advised to switch it:
  https://lore.kernel.org/lkml/034a302d-773d-5bdb-a32b-bd283d6c7710@redhat.com/

I'm happy to go back if that's really preferred.  But the current
style also matches __mutex_lock_common's nesting.


> > @@ -1775,8 +1782,9 @@ static int __sched rt_mutex_slowlock(struct rt_mutex_base *lock,
> >        * irqsave/restore variants.
> >        */
> >       raw_spin_lock_irqsave(&lock->wait_lock, flags);
> > -     ret = __rt_mutex_slowlock_locked(lock, ww_ctx, state);
> > +     ret = __rt_mutex_slowlock_locked(lock, ww_ctx, state, &wake_q);
> >       raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
> > +     wake_up_q(&wake_q);
>
> Shouldn't this also be wrapped in a preempt-disabled region?
>
> >       rt_mutex_post_schedule();
> >
> >       return ret;
>
> > @@ -122,6 +123,7 @@ static int __sched __rwbase_read_lock(struct rwbase_rt *rwb,
> >       if (!ret)
> >               atomic_inc(&rwb->readers);
> >       raw_spin_unlock_irq(&rtm->wait_lock);
> > +     wake_up_q(&wake_q);
>
> Same question wrt preemption.

Yeah, thanks for pointing out that inconsistency. I'll rework and test
with that.

thanks again for the review and feedback!
-john

[RESEND][PATCH v9 2/7] locking/mutex: Make mutex::wait_lock irq safe

[John Stultz]

From: Juri Lelli <juri.lelli@redhat.com>

mutex::wait_lock might be nested under rq->lock.

Make it irq safe then.

Cc: Joel Fernandes <joelaf@google.com>
Cc: Qais Yousef <qyousef@google.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Valentin Schneider <vschneid@redhat.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Ben Segall <bsegall@google.com>
Cc: Zimuzo Ezeozue <zezeozue@google.com>
Cc: Youssef Esmat <youssefesmat@google.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Daniel Bristot de Oliveira <bristot@redhat.com>
Cc: Will Deacon <will@kernel.org>
Cc: Waiman Long <longman@redhat.com>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Metin Kaya <Metin.Kaya@arm.com>
Cc: Xuewen Yan <xuewen.yan94@gmail.com>
Cc: K Prateek Nayak <kprateek.nayak@amd.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: kernel-team@android.com
Tested-by: K Prateek Nayak <kprateek.nayak@amd.com>
Signed-off-by: Juri Lelli <juri.lelli@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
[rebase & fix {un,}lock_wait_lock helpers in ww_mutex.h]
Signed-off-by: Connor O'Brien <connoro@google.com>
Signed-off-by: John Stultz <jstultz@google.com>
---
v3:
* Re-added this patch after it was dropped in v2 which
  caused lockdep warnings to trip.
v7:
* Fix function definition for PREEMPT_RT case, as pointed out
  by Metin Kaya.
* Fix incorrect flags handling in PREEMPT_RT case as found by
  Metin Kaya
---
 kernel/locking/mutex.c    | 18 ++++++++++--------
 kernel/locking/ww_mutex.h | 22 +++++++++++-----------
 2 files changed, 21 insertions(+), 19 deletions(-)

diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c
index 980ce630232c..7de72c610c65 100644
--- a/kernel/locking/mutex.c
+++ b/kernel/locking/mutex.c
@@ -578,6 +578,7 @@ __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclas
 	DEFINE_WAKE_Q(wake_q);
 	struct mutex_waiter waiter;
 	struct ww_mutex *ww;
+	unsigned long flags;
 	int ret;
 
 	if (!use_ww_ctx)
@@ -620,7 +621,7 @@ __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclas
 		return 0;
 	}
 
-	raw_spin_lock(&lock->wait_lock);
+	raw_spin_lock_irqsave(&lock->wait_lock, flags);
 	/*
 	 * After waiting to acquire the wait_lock, try again.
 	 */
@@ -681,7 +682,7 @@ __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclas
 				goto err;
 		}
 
-		raw_spin_unlock(&lock->wait_lock);
+		raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
 		/* Make sure we do wakeups before calling schedule */
 		if (!wake_q_empty(&wake_q)) {
 			wake_up_q(&wake_q);
@@ -707,9 +708,9 @@ __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclas
 			trace_contention_begin(lock, LCB_F_MUTEX);
 		}
 
-		raw_spin_lock(&lock->wait_lock);
+		raw_spin_lock_irqsave(&lock->wait_lock, flags);
 	}
-	raw_spin_lock(&lock->wait_lock);
+	raw_spin_lock_irqsave(&lock->wait_lock, flags);
 acquired:
 	__set_current_state(TASK_RUNNING);
 
@@ -735,7 +736,7 @@ __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclas
 	if (ww_ctx)
 		ww_mutex_lock_acquired(ww, ww_ctx);
 
-	raw_spin_unlock(&lock->wait_lock);
+	raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
 	wake_up_q(&wake_q);
 	preempt_enable();
 	return 0;
@@ -745,7 +746,7 @@ __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclas
 	__mutex_remove_waiter(lock, &waiter);
 err_early_kill:
 	trace_contention_end(lock, ret);
-	raw_spin_unlock(&lock->wait_lock);
+	raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
 	debug_mutex_free_waiter(&waiter);
 	mutex_release(&lock->dep_map, ip);
 	wake_up_q(&wake_q);
@@ -916,6 +917,7 @@ static noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigne
 	struct task_struct *next = NULL;
 	DEFINE_WAKE_Q(wake_q);
 	unsigned long owner;
+	unsigned long flags;
 
 	mutex_release(&lock->dep_map, ip);
 
@@ -943,7 +945,7 @@ static noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigne
 	}
 
 	preempt_disable();
-	raw_spin_lock(&lock->wait_lock);
+	raw_spin_lock_irqsave(&lock->wait_lock, flags);
 	debug_mutex_unlock(lock);
 	if (!list_empty(&lock->wait_list)) {
 		/* get the first entry from the wait-list: */
@@ -960,7 +962,7 @@ static noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigne
 	if (owner & MUTEX_FLAG_HANDOFF)
 		__mutex_handoff(lock, next);
 
-	raw_spin_unlock(&lock->wait_lock);
+	raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
 	wake_up_q(&wake_q);
 	preempt_enable();
 }
diff --git a/kernel/locking/ww_mutex.h b/kernel/locking/ww_mutex.h
index 7189c6631d90..9facc0ddfdd3 100644
--- a/kernel/locking/ww_mutex.h
+++ b/kernel/locking/ww_mutex.h
@@ -70,14 +70,14 @@ __ww_mutex_has_waiters(struct mutex *lock)
 	return atomic_long_read(&lock->owner) & MUTEX_FLAG_WAITERS;
 }
 
-static inline void lock_wait_lock(struct mutex *lock)
+static inline void lock_wait_lock(struct mutex *lock, unsigned long *flags)
 {
-	raw_spin_lock(&lock->wait_lock);
+	raw_spin_lock_irqsave(&lock->wait_lock, *flags);
 }
 
-static inline void unlock_wait_lock(struct mutex *lock)
+static inline void unlock_wait_lock(struct mutex *lock, unsigned long *flags)
 {
-	raw_spin_unlock(&lock->wait_lock);
+	raw_spin_unlock_irqrestore(&lock->wait_lock, *flags);
 }
 
 static inline void lockdep_assert_wait_lock_held(struct mutex *lock)
@@ -144,14 +144,14 @@ __ww_mutex_has_waiters(struct rt_mutex *lock)
 	return rt_mutex_has_waiters(&lock->rtmutex);
 }
 
-static inline void lock_wait_lock(struct rt_mutex *lock)
+static inline void lock_wait_lock(struct rt_mutex *lock, unsigned long *flags)
 {
-	raw_spin_lock(&lock->rtmutex.wait_lock);
+	raw_spin_lock_irqsave(&lock->rtmutex.wait_lock, *flags);
 }
 
-static inline void unlock_wait_lock(struct rt_mutex *lock)
+static inline void unlock_wait_lock(struct rt_mutex *lock, unsigned long *flags)
 {
-	raw_spin_unlock(&lock->rtmutex.wait_lock);
+	raw_spin_unlock_irqrestore(&lock->rtmutex.wait_lock, *flags);
 }
 
 static inline void lockdep_assert_wait_lock_held(struct rt_mutex *lock)
@@ -380,6 +380,7 @@ static __always_inline void
 ww_mutex_set_context_fastpath(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
 {
 	DEFINE_WAKE_Q(wake_q);
+	unsigned long flags;
 
 	ww_mutex_lock_acquired(lock, ctx);
 
@@ -408,10 +409,9 @@ ww_mutex_set_context_fastpath(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
 	 * Uh oh, we raced in fastpath, check if any of the waiters need to
 	 * die or wound us.
 	 */
-	lock_wait_lock(&lock->base);
+	lock_wait_lock(&lock->base, &flags);
 	__ww_mutex_check_waiters(&lock->base, ctx, &wake_q);
-	unlock_wait_lock(&lock->base);
-
+	unlock_wait_lock(&lock->base, &flags);
 	wake_up_q(&wake_q);
 }
 
-- 
2.44.0.478.gd926399ef9-goog

Re: [RESEND][PATCH v9 2/7] locking/mutex: Make mutex::wait_lock irq safe

[Valentin Schneider]

On 01/04/24 16:44, John Stultz wrote:
> From: Juri Lelli <juri.lelli@redhat.com>
>
> mutex::wait_lock might be nested under rq->lock.
>
> Make it irq safe then.
>
> Cc: Joel Fernandes <joelaf@google.com>
> Cc: Qais Yousef <qyousef@google.com>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Juri Lelli <juri.lelli@redhat.com>
> Cc: Vincent Guittot <vincent.guittot@linaro.org>
> Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
> Cc: Valentin Schneider <vschneid@redhat.com>
> Cc: Steven Rostedt <rostedt@goodmis.org>
> Cc: Ben Segall <bsegall@google.com>
> Cc: Zimuzo Ezeozue <zezeozue@google.com>
> Cc: Youssef Esmat <youssefesmat@google.com>
> Cc: Mel Gorman <mgorman@suse.de>
> Cc: Daniel Bristot de Oliveira <bristot@redhat.com>
> Cc: Will Deacon <will@kernel.org>
> Cc: Waiman Long <longman@redhat.com>
> Cc: Boqun Feng <boqun.feng@gmail.com>
> Cc: "Paul E. McKenney" <paulmck@kernel.org>
> Cc: Metin Kaya <Metin.Kaya@arm.com>
> Cc: Xuewen Yan <xuewen.yan94@gmail.com>
> Cc: K Prateek Nayak <kprateek.nayak@amd.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: kernel-team@android.com
> Tested-by: K Prateek Nayak <kprateek.nayak@amd.com>

Reviewed-by: Valentin Schneider <vschneid@redhat.com>

> Signed-off-by: Juri Lelli <juri.lelli@redhat.com>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> [rebase & fix {un,}lock_wait_lock helpers in ww_mutex.h]
> Signed-off-by: Connor O'Brien <connoro@google.com>
> Signed-off-by: John Stultz <jstultz@google.com>

[RESEND][PATCH v9 3/7] locking/mutex: Expose __mutex_owner()

[John Stultz]

From: Juri Lelli <juri.lelli@redhat.com>

Implementing proxy execution requires that scheduler code be able to
identify the current owner of a mutex. Expose __mutex_owner() for
this purpose (alone!).

Cc: Joel Fernandes <joelaf@google.com>
Cc: Qais Yousef <qyousef@google.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Valentin Schneider <vschneid@redhat.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Ben Segall <bsegall@google.com>
Cc: Zimuzo Ezeozue <zezeozue@google.com>
Cc: Youssef Esmat <youssefesmat@google.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Daniel Bristot de Oliveira <bristot@redhat.com>
Cc: Will Deacon <will@kernel.org>
Cc: Waiman Long <longman@redhat.com>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Metin Kaya <Metin.Kaya@arm.com>
Cc: Xuewen Yan <xuewen.yan94@gmail.com>
Cc: K Prateek Nayak <kprateek.nayak@amd.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: kernel-team@android.com
Tested-by: K Prateek Nayak <kprateek.nayak@amd.com>
Signed-off-by: Juri Lelli <juri.lelli@redhat.com>
[Removed the EXPORT_SYMBOL]
Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
Signed-off-by: Connor O'Brien <connoro@google.com>
[jstultz: Reworked per Peter's suggestions]
Signed-off-by: John Stultz <jstultz@google.com>
---
v4:
* Move __mutex_owner() to kernel/locking/mutex.h instead of
  adding a new globally available accessor function to keep
  the exposure of this low, along with keeping it an inline
  function, as suggested by PeterZ
---
 kernel/locking/mutex.c | 25 -------------------------
 kernel/locking/mutex.h | 25 +++++++++++++++++++++++++
 2 files changed, 25 insertions(+), 25 deletions(-)

diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c
index 7de72c610c65..5741641be914 100644
--- a/kernel/locking/mutex.c
+++ b/kernel/locking/mutex.c
@@ -56,31 +56,6 @@ __mutex_init(struct mutex *lock, const char *name, struct lock_class_key *key)
 }
 EXPORT_SYMBOL(__mutex_init);
 
-/*
- * @owner: contains: 'struct task_struct *' to the current lock owner,
- * NULL means not owned. Since task_struct pointers are aligned at
- * at least L1_CACHE_BYTES, we have low bits to store extra state.
- *
- * Bit0 indicates a non-empty waiter list; unlock must issue a wakeup.
- * Bit1 indicates unlock needs to hand the lock to the top-waiter
- * Bit2 indicates handoff has been done and we're waiting for pickup.
- */
-#define MUTEX_FLAG_WAITERS	0x01
-#define MUTEX_FLAG_HANDOFF	0x02
-#define MUTEX_FLAG_PICKUP	0x04
-
-#define MUTEX_FLAGS		0x07
-
-/*
- * Internal helper function; C doesn't allow us to hide it :/
- *
- * DO NOT USE (outside of mutex code).
- */
-static inline struct task_struct *__mutex_owner(struct mutex *lock)
-{
-	return (struct task_struct *)(atomic_long_read(&lock->owner) & ~MUTEX_FLAGS);
-}
-
 static inline struct task_struct *__owner_task(unsigned long owner)
 {
 	return (struct task_struct *)(owner & ~MUTEX_FLAGS);
diff --git a/kernel/locking/mutex.h b/kernel/locking/mutex.h
index 0b2a79c4013b..1c7d3d32def8 100644
--- a/kernel/locking/mutex.h
+++ b/kernel/locking/mutex.h
@@ -20,6 +20,31 @@ struct mutex_waiter {
 #endif
 };
 
+/*
+ * @owner: contains: 'struct task_struct *' to the current lock owner,
+ * NULL means not owned. Since task_struct pointers are aligned at
+ * at least L1_CACHE_BYTES, we have low bits to store extra state.
+ *
+ * Bit0 indicates a non-empty waiter list; unlock must issue a wakeup.
+ * Bit1 indicates unlock needs to hand the lock to the top-waiter
+ * Bit2 indicates handoff has been done and we're waiting for pickup.
+ */
+#define MUTEX_FLAG_WAITERS	0x01
+#define MUTEX_FLAG_HANDOFF	0x02
+#define MUTEX_FLAG_PICKUP	0x04
+
+#define MUTEX_FLAGS		0x07
+
+/*
+ * Internal helper function; C doesn't allow us to hide it :/
+ *
+ * DO NOT USE (outside of mutex & scheduler code).
+ */
+static inline struct task_struct *__mutex_owner(struct mutex *lock)
+{
+	return (struct task_struct *)(atomic_long_read(&lock->owner) & ~MUTEX_FLAGS);
+}
+
 #ifdef CONFIG_DEBUG_MUTEXES
 extern void debug_mutex_lock_common(struct mutex *lock,
 				    struct mutex_waiter *waiter);
-- 
2.44.0.478.gd926399ef9-goog

Re: [RESEND][PATCH v9 3/7] locking/mutex: Expose __mutex_owner()

[Valentin Schneider]

On 01/04/24 16:44, John Stultz wrote:
> From: Juri Lelli <juri.lelli@redhat.com>
>
> Implementing proxy execution requires that scheduler code be able to
> identify the current owner of a mutex. Expose __mutex_owner() for
> this purpose (alone!).
>
> Cc: Joel Fernandes <joelaf@google.com>
> Cc: Qais Yousef <qyousef@google.com>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Juri Lelli <juri.lelli@redhat.com>
> Cc: Vincent Guittot <vincent.guittot@linaro.org>
> Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
> Cc: Valentin Schneider <vschneid@redhat.com>
> Cc: Steven Rostedt <rostedt@goodmis.org>
> Cc: Ben Segall <bsegall@google.com>
> Cc: Zimuzo Ezeozue <zezeozue@google.com>
> Cc: Youssef Esmat <youssefesmat@google.com>
> Cc: Mel Gorman <mgorman@suse.de>
> Cc: Daniel Bristot de Oliveira <bristot@redhat.com>
> Cc: Will Deacon <will@kernel.org>
> Cc: Waiman Long <longman@redhat.com>
> Cc: Boqun Feng <boqun.feng@gmail.com>
> Cc: "Paul E. McKenney" <paulmck@kernel.org>
> Cc: Metin Kaya <Metin.Kaya@arm.com>
> Cc: Xuewen Yan <xuewen.yan94@gmail.com>
> Cc: K Prateek Nayak <kprateek.nayak@amd.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: kernel-team@android.com
> Tested-by: K Prateek Nayak <kprateek.nayak@amd.com>

Reviewed-by: Valentin Schneider <vschneid@redhat.com>

> Signed-off-by: Juri Lelli <juri.lelli@redhat.com>
> [Removed the EXPORT_SYMBOL]
> Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
> Signed-off-by: Connor O'Brien <connoro@google.com>
> [jstultz: Reworked per Peter's suggestions]
> Signed-off-by: John Stultz <jstultz@google.com>

[RESEND][PATCH v9 4/7] sched: Add do_push_task helper

[John Stultz]

From: Connor O'Brien <connoro@google.com>

Switch logic that deactivates, sets the task cpu,
and reactivates a task on a different rq to use a
helper that will be later extended to push entire
blocked task chains.

This patch was broken out from a larger chain migration
patch originally by Connor O'Brien.

Cc: Joel Fernandes <joelaf@google.com>
Cc: Qais Yousef <qyousef@google.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Valentin Schneider <vschneid@redhat.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Ben Segall <bsegall@google.com>
Cc: Zimuzo Ezeozue <zezeozue@google.com>
Cc: Youssef Esmat <youssefesmat@google.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Daniel Bristot de Oliveira <bristot@redhat.com>
Cc: Will Deacon <will@kernel.org>
Cc: Waiman Long <longman@redhat.com>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Metin Kaya <Metin.Kaya@arm.com>
Cc: Xuewen Yan <xuewen.yan94@gmail.com>
Cc: K Prateek Nayak <kprateek.nayak@amd.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: kernel-team@android.com
Tested-by: K Prateek Nayak <kprateek.nayak@amd.com>
Signed-off-by: Connor O'Brien <connoro@google.com>
[jstultz: split out from larger chain migration patch]
Signed-off-by: John Stultz <jstultz@google.com>
---
v8:
* Renamed from push_task_chain to do_push_task so it makes
  more sense without proxy-execution
---
 kernel/sched/core.c     | 4 +---
 kernel/sched/deadline.c | 8 ++------
 kernel/sched/rt.c       | 8 ++------
 kernel/sched/sched.h    | 9 +++++++++
 4 files changed, 14 insertions(+), 15 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 7019a40457a6..586a3f8186bd 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2712,9 +2712,7 @@ int push_cpu_stop(void *arg)
 
 	// XXX validate p is still the highest prio task
 	if (task_rq(p) == rq) {
-		deactivate_task(rq, p, 0);
-		set_task_cpu(p, lowest_rq->cpu);
-		activate_task(lowest_rq, p, 0);
+		do_push_task(rq, lowest_rq, p);
 		resched_curr(lowest_rq);
 	}
 
diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index a04a436af8cc..e68d88963e89 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -2443,9 +2443,7 @@ static int push_dl_task(struct rq *rq)
 		goto retry;
 	}
 
-	deactivate_task(rq, next_task, 0);
-	set_task_cpu(next_task, later_rq->cpu);
-	activate_task(later_rq, next_task, 0);
+	do_push_task(rq, later_rq, next_task);
 	ret = 1;
 
 	resched_curr(later_rq);
@@ -2531,9 +2529,7 @@ static void pull_dl_task(struct rq *this_rq)
 			if (is_migration_disabled(p)) {
 				push_task = get_push_task(src_rq);
 			} else {
-				deactivate_task(src_rq, p, 0);
-				set_task_cpu(p, this_cpu);
-				activate_task(this_rq, p, 0);
+				do_push_task(src_rq, this_rq, p);
 				dmin = p->dl.deadline;
 				resched = true;
 			}
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 3261b067b67e..dd072d11cc02 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -2106,9 +2106,7 @@ static int push_rt_task(struct rq *rq, bool pull)
 		goto retry;
 	}
 
-	deactivate_task(rq, next_task, 0);
-	set_task_cpu(next_task, lowest_rq->cpu);
-	activate_task(lowest_rq, next_task, 0);
+	do_push_task(rq, lowest_rq, next_task);
 	resched_curr(lowest_rq);
 	ret = 1;
 
@@ -2379,9 +2377,7 @@ static void pull_rt_task(struct rq *this_rq)
 			if (is_migration_disabled(p)) {
 				push_task = get_push_task(src_rq);
 			} else {
-				deactivate_task(src_rq, p, 0);
-				set_task_cpu(p, this_cpu);
-				activate_task(this_rq, p, 0);
+				do_push_task(src_rq, this_rq, p);
 				resched = true;
 			}
 			/*
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index d2242679239e..16057de24ecd 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -3472,5 +3472,14 @@ static inline void init_sched_mm_cid(struct task_struct *t) { }
 
 extern u64 avg_vruntime(struct cfs_rq *cfs_rq);
 extern int entity_eligible(struct cfs_rq *cfs_rq, struct sched_entity *se);
+#ifdef CONFIG_SMP
+static inline
+void do_push_task(struct rq *rq, struct rq *dst_rq, struct task_struct *task)
+{
+	deactivate_task(rq, task, 0);
+	set_task_cpu(task, dst_rq->cpu);
+	activate_task(dst_rq, task, 0);
+}
+#endif
 
 #endif /* _KERNEL_SCHED_SCHED_H */
-- 
2.44.0.478.gd926399ef9-goog

Re: [RESEND][PATCH v9 4/7] sched: Add do_push_task helper

[Valentin Schneider]

On 01/04/24 16:44, John Stultz wrote:
> From: Connor O'Brien <connoro@google.com>
>
> Switch logic that deactivates, sets the task cpu,
> and reactivates a task on a different rq to use a
> helper that will be later extended to push entire
> blocked task chains.
>
> This patch was broken out from a larger chain migration
> patch originally by Connor O'Brien.
>
> Cc: Joel Fernandes <joelaf@google.com>
> Cc: Qais Yousef <qyousef@google.com>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Juri Lelli <juri.lelli@redhat.com>
> Cc: Vincent Guittot <vincent.guittot@linaro.org>
> Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
> Cc: Valentin Schneider <vschneid@redhat.com>
> Cc: Steven Rostedt <rostedt@goodmis.org>
> Cc: Ben Segall <bsegall@google.com>
> Cc: Zimuzo Ezeozue <zezeozue@google.com>
> Cc: Youssef Esmat <youssefesmat@google.com>
> Cc: Mel Gorman <mgorman@suse.de>
> Cc: Daniel Bristot de Oliveira <bristot@redhat.com>
> Cc: Will Deacon <will@kernel.org>
> Cc: Waiman Long <longman@redhat.com>
> Cc: Boqun Feng <boqun.feng@gmail.com>
> Cc: "Paul E. McKenney" <paulmck@kernel.org>
> Cc: Metin Kaya <Metin.Kaya@arm.com>
> Cc: Xuewen Yan <xuewen.yan94@gmail.com>
> Cc: K Prateek Nayak <kprateek.nayak@amd.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: kernel-team@android.com
> Tested-by: K Prateek Nayak <kprateek.nayak@amd.com>

Naming nit below notwithstanding:

Reviewed-by: Valentin Schneider <vschneid@redhat.com>

> Signed-off-by: Connor O'Brien <connoro@google.com>
> [jstultz: split out from larger chain migration patch]
> Signed-off-by: John Stultz <jstultz@google.com>

> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> index d2242679239e..16057de24ecd 100644
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -3472,5 +3472,14 @@ static inline void init_sched_mm_cid(struct task_struct *t) { }
>  
>  extern u64 avg_vruntime(struct cfs_rq *cfs_rq);
>  extern int entity_eligible(struct cfs_rq *cfs_rq, struct sched_entity *se);
> +#ifdef CONFIG_SMP
> +static inline
> +void do_push_task(struct rq *rq, struct rq *dst_rq, struct task_struct *task)

The naming IMO unfortunately clashes with the hotplug push_task /
balance_push() stuff.

AFAICT this is move_queued_task() but in a double rq lock
context. How about move_queued_task_locked()?

Interestingly, all the patched call sites end up with a resched_curr(), but
move_queued_task() has wakeup_preempt() instead.  

> +{
> +	deactivate_task(rq, task, 0);
> +	set_task_cpu(task, dst_rq->cpu);
> +	activate_task(dst_rq, task, 0);
> +}
> +#endif
>  
>  #endif /* _KERNEL_SCHED_SCHED_H */
> -- 
> 2.44.0.478.gd926399ef9-goog

Re: [RESEND][PATCH v9 4/7] sched: Add do_push_task helper

[John Stultz]

On Tue, Apr 9, 2024 at 9:30 AM Valentin Schneider <vschneid@redhat.com> wrote:
> Naming nit below notwithstanding:
>
> Reviewed-by: Valentin Schneider <vschneid@redhat.com>

Hey! Thanks so much for taking a look and providing this feedback! I
really appreciate it!

> > +static inline
> > +void do_push_task(struct rq *rq, struct rq *dst_rq, struct task_struct *task)
>
> The naming IMO unfortunately clashes with the hotplug push_task /
> balance_push() stuff.
>
> AFAICT this is move_queued_task() but in a double rq lock
> context. How about move_queued_task_locked()?

Sounds good to me! Changed in my pre-v10 tree.


> Interestingly, all the patched call sites end up with a resched_curr(), but
> move_queued_task() has wakeup_preempt() instead.

Yeah. I'll look a bit more to see if I can find a way to fold the
resched in as well, and try to make sure I understand the subtle
difference in move_queued_task() - I don't want the name similarity to
confuse if the behavior is different.

Again, thanks so much for the feedback and review!
-john

[RESEND][PATCH v9 5/7] sched: Consolidate pick_*_task to task_is_pushable helper

[John Stultz]

From: Connor O'Brien <connoro@google.com>

This patch consolidates rt and deadline pick_*_task functions to
a task_is_pushable() helper

This patch was broken out from a larger chain migration
patch originally by Connor O'Brien.

Cc: Joel Fernandes <joelaf@google.com>
Cc: Qais Yousef <qyousef@google.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Valentin Schneider <vschneid@redhat.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Ben Segall <bsegall@google.com>
Cc: Zimuzo Ezeozue <zezeozue@google.com>
Cc: Youssef Esmat <youssefesmat@google.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Daniel Bristot de Oliveira <bristot@redhat.com>
Cc: Will Deacon <will@kernel.org>
Cc: Waiman Long <longman@redhat.com>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Metin Kaya <Metin.Kaya@arm.com>
Cc: Xuewen Yan <xuewen.yan94@gmail.com>
Cc: K Prateek Nayak <kprateek.nayak@amd.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: kernel-team@android.com
Tested-by: K Prateek Nayak <kprateek.nayak@amd.com>
Signed-off-by: Connor O'Brien <connoro@google.com>
[jstultz: split out from larger chain migration patch,
 renamed helper function]
Signed-off-by: John Stultz <jstultz@google.com>
---
v7:
* Split from chain migration patch
* Renamed function
---
 kernel/sched/deadline.c | 10 +---------
 kernel/sched/rt.c       | 11 +----------
 kernel/sched/sched.h    | 10 ++++++++++
 3 files changed, 12 insertions(+), 19 deletions(-)

diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index e68d88963e89..1b9cdb507498 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -2179,14 +2179,6 @@ static void task_fork_dl(struct task_struct *p)
 /* Only try algorithms three times */
 #define DL_MAX_TRIES 3
 
-static int pick_dl_task(struct rq *rq, struct task_struct *p, int cpu)
-{
-	if (!task_on_cpu(rq, p) &&
-	    cpumask_test_cpu(cpu, &p->cpus_mask))
-		return 1;
-	return 0;
-}
-
 /*
  * Return the earliest pushable rq's task, which is suitable to be executed
  * on the CPU, NULL otherwise:
@@ -2205,7 +2197,7 @@ static struct task_struct *pick_earliest_pushable_dl_task(struct rq *rq, int cpu
 	if (next_node) {
 		p = __node_2_pdl(next_node);
 
-		if (pick_dl_task(rq, p, cpu))
+		if (task_is_pushable(rq, p, cpu) == 1)
 			return p;
 
 		next_node = rb_next(next_node);
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index dd072d11cc02..638e7c158ae4 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -1791,15 +1791,6 @@ static void put_prev_task_rt(struct rq *rq, struct task_struct *p)
 /* Only try algorithms three times */
 #define RT_MAX_TRIES 3
 
-static int pick_rt_task(struct rq *rq, struct task_struct *p, int cpu)
-{
-	if (!task_on_cpu(rq, p) &&
-	    cpumask_test_cpu(cpu, &p->cpus_mask))
-		return 1;
-
-	return 0;
-}
-
 /*
  * Return the highest pushable rq's task, which is suitable to be executed
  * on the CPU, NULL otherwise
@@ -1813,7 +1804,7 @@ static struct task_struct *pick_highest_pushable_task(struct rq *rq, int cpu)
 		return NULL;
 
 	plist_for_each_entry(p, head, pushable_tasks) {
-		if (pick_rt_task(rq, p, cpu))
+		if (task_is_pushable(rq, p, cpu) == 1)
 			return p;
 	}
 
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 16057de24ecd..f25eec405df9 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -3480,6 +3480,16 @@ void do_push_task(struct rq *rq, struct rq *dst_rq, struct task_struct *task)
 	set_task_cpu(task, dst_rq->cpu);
 	activate_task(dst_rq, task, 0);
 }
+
+static inline
+int task_is_pushable(struct rq *rq, struct task_struct *p, int cpu)
+{
+	if (!task_on_cpu(rq, p) &&
+	    cpumask_test_cpu(cpu, &p->cpus_mask))
+		return 1;
+
+	return 0;
+}
 #endif
 
 #endif /* _KERNEL_SCHED_SCHED_H */
-- 
2.44.0.478.gd926399ef9-goog

Re: [RESEND][PATCH v9 5/7] sched: Consolidate pick_*_task to task_is_pushable helper

[Valentin Schneider]

On 01/04/24 16:44, John Stultz wrote:
> From: Connor O'Brien <connoro@google.com>
>
> This patch consolidates rt and deadline pick_*_task functions to
> a task_is_pushable() helper
>
> This patch was broken out from a larger chain migration
> patch originally by Connor O'Brien.
>
> Cc: Joel Fernandes <joelaf@google.com>
> Cc: Qais Yousef <qyousef@google.com>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Juri Lelli <juri.lelli@redhat.com>
> Cc: Vincent Guittot <vincent.guittot@linaro.org>
> Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
> Cc: Valentin Schneider <vschneid@redhat.com>
> Cc: Steven Rostedt <rostedt@goodmis.org>
> Cc: Ben Segall <bsegall@google.com>
> Cc: Zimuzo Ezeozue <zezeozue@google.com>
> Cc: Youssef Esmat <youssefesmat@google.com>
> Cc: Mel Gorman <mgorman@suse.de>
> Cc: Daniel Bristot de Oliveira <bristot@redhat.com>
> Cc: Will Deacon <will@kernel.org>
> Cc: Waiman Long <longman@redhat.com>
> Cc: Boqun Feng <boqun.feng@gmail.com>
> Cc: "Paul E. McKenney" <paulmck@kernel.org>
> Cc: Metin Kaya <Metin.Kaya@arm.com>
> Cc: Xuewen Yan <xuewen.yan94@gmail.com>
> Cc: K Prateek Nayak <kprateek.nayak@amd.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: kernel-team@android.com
> Tested-by: K Prateek Nayak <kprateek.nayak@amd.com>

Reviewed-by: Valentin Schneider <vschneid@redhat.com>

> Signed-off-by: Connor O'Brien <connoro@google.com>
> [jstultz: split out from larger chain migration patch,
>  renamed helper function]
> Signed-off-by: John Stultz <jstultz@google.com>

[RESEND][PATCH v9 6/7] sched: Split out __schedule() deactivate task logic into a helper

[John Stultz]

As we're going to re-use the deactivation logic,
split it into a helper.

Cc: Joel Fernandes <joelaf@google.com>
Cc: Qais Yousef <qyousef@google.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Valentin Schneider <vschneid@redhat.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Ben Segall <bsegall@google.com>
Cc: Zimuzo Ezeozue <zezeozue@google.com>
Cc: Youssef Esmat <youssefesmat@google.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Daniel Bristot de Oliveira <bristot@redhat.com>
Cc: Will Deacon <will@kernel.org>
Cc: Waiman Long <longman@redhat.com>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Metin Kaya <Metin.Kaya@arm.com>
Cc: Xuewen Yan <xuewen.yan94@gmail.com>
Cc: K Prateek Nayak <kprateek.nayak@amd.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: kernel-team@android.com
Tested-by: K Prateek Nayak <kprateek.nayak@amd.com>
Signed-off-by: John Stultz <jstultz@google.com>
---
v6:
* Define function as static to avoid "no previous prototype"
  warnings as Reported-by: kernel test robot <lkp@intel.com>
v7:
* Rename state task_state to be more clear, as suggested by
  Metin Kaya
---
 kernel/sched/core.c | 72 +++++++++++++++++++++++++++------------------
 1 file changed, 43 insertions(+), 29 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 586a3f8186bd..0eaa0855ef86 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -6572,6 +6572,48 @@ pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
 # define SM_MASK_PREEMPT	SM_PREEMPT
 #endif
 
+/*
+ * Helper function for __schedule()
+ *
+ * If a task does not have signals pending, deactivate it and return true
+ * Otherwise marks the task's __state as RUNNING and returns false
+ */
+static bool try_to_deactivate_task(struct rq *rq, struct task_struct *p,
+				   unsigned long task_state)
+{
+	if (signal_pending_state(task_state, p)) {
+		WRITE_ONCE(p->__state, TASK_RUNNING);
+	} else {
+		p->sched_contributes_to_load =
+			(task_state & TASK_UNINTERRUPTIBLE) &&
+			!(task_state & TASK_NOLOAD) &&
+			!(task_state & TASK_FROZEN);
+
+		if (p->sched_contributes_to_load)
+			rq->nr_uninterruptible++;
+
+		/*
+		 * __schedule()			ttwu()
+		 *   prev_state = prev->state;    if (p->on_rq && ...)
+		 *   if (prev_state)		    goto out;
+		 *     p->on_rq = 0;		  smp_acquire__after_ctrl_dep();
+		 *				  p->state = TASK_WAKING
+		 *
+		 * Where __schedule() and ttwu() have matching control dependencies.
+		 *
+		 * After this, schedule() must not care about p->state any more.
+		 */
+		deactivate_task(rq, p, DEQUEUE_SLEEP | DEQUEUE_NOCLOCK);
+
+		if (p->in_iowait) {
+			atomic_inc(&rq->nr_iowait);
+			delayacct_blkio_start();
+		}
+		return true;
+	}
+	return false;
+}
+
 /*
  * __schedule() is the main scheduler function.
  *
@@ -6665,35 +6707,7 @@ static void __sched notrace __schedule(unsigned int sched_mode)
 	 */
 	prev_state = READ_ONCE(prev->__state);
 	if (!(sched_mode & SM_MASK_PREEMPT) && prev_state) {
-		if (signal_pending_state(prev_state, prev)) {
-			WRITE_ONCE(prev->__state, TASK_RUNNING);
-		} else {
-			prev->sched_contributes_to_load =
-				(prev_state & TASK_UNINTERRUPTIBLE) &&
-				!(prev_state & TASK_NOLOAD) &&
-				!(prev_state & TASK_FROZEN);
-
-			if (prev->sched_contributes_to_load)
-				rq->nr_uninterruptible++;
-
-			/*
-			 * __schedule()			ttwu()
-			 *   prev_state = prev->state;    if (p->on_rq && ...)
-			 *   if (prev_state)		    goto out;
-			 *     p->on_rq = 0;		  smp_acquire__after_ctrl_dep();
-			 *				  p->state = TASK_WAKING
-			 *
-			 * Where __schedule() and ttwu() have matching control dependencies.
-			 *
-			 * After this, schedule() must not care about p->state any more.
-			 */
-			deactivate_task(rq, prev, DEQUEUE_SLEEP | DEQUEUE_NOCLOCK);
-
-			if (prev->in_iowait) {
-				atomic_inc(&rq->nr_iowait);
-				delayacct_blkio_start();
-			}
-		}
+		try_to_deactivate_task(rq, prev, prev_state);
 		switch_count = &prev->nvcsw;
 	}
 
-- 
2.44.0.478.gd926399ef9-goog

[RESEND][PATCH v9 7/7] sched: Split scheduler and execution contexts

[John Stultz]

From: Peter Zijlstra <peterz@infradead.org>

Let's define the scheduling context as all the scheduler state
in task_struct for the task selected to run, and the execution
context as all state required to actually run the task.

Currently both are intertwined in task_struct. We want to
logically split these such that we can use the scheduling
context of the task selected to be scheduled, but use the
execution context of a different task to actually be run.

To this purpose, introduce rq_selected() macro to point to the
task_struct selected from the runqueue by the scheduler, and
will be used for scheduler state, and preserve rq->curr to
indicate the execution context of the task that will actually be
run.

Cc: Joel Fernandes <joelaf@google.com>
Cc: Qais Yousef <qyousef@google.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Valentin Schneider <vschneid@redhat.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Ben Segall <bsegall@google.com>
Cc: Zimuzo Ezeozue <zezeozue@google.com>
Cc: Youssef Esmat <youssefesmat@google.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Daniel Bristot de Oliveira <bristot@redhat.com>
Cc: Will Deacon <will@kernel.org>
Cc: Waiman Long <longman@redhat.com>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Xuewen Yan <xuewen.yan94@gmail.com>
Cc: K Prateek Nayak <kprateek.nayak@amd.com>
Cc: Metin Kaya <Metin.Kaya@arm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: kernel-team@android.com
Tested-by: K Prateek Nayak <kprateek.nayak@amd.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Juri Lelli <juri.lelli@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20181009092434.26221-5-juri.lelli@redhat.com
[add additional comments and update more sched_class code to use
 rq::proxy]
Signed-off-by: Connor O'Brien <connoro@google.com>
[jstultz: Rebased and resolved minor collisions, reworked to use
 accessors, tweaked update_curr_common to use rq_proxy fixing rt
 scheduling issues]
Signed-off-by: John Stultz <jstultz@google.com>
---
v2:
* Reworked to use accessors
* Fixed update_curr_common to use proxy instead of curr
v3:
* Tweaked wrapper names
* Swapped proxy for selected for clarity
v4:
* Minor variable name tweaks for readability
* Use a macro instead of a inline function and drop
  other helper functions as suggested by Peter.
* Remove verbose comments/questions to avoid review
  distractions, as suggested by Dietmar
v5:
* Add CONFIG_PROXY_EXEC option to this patch so the
  new logic can be tested with this change
* Minor fix to grab rq_selected when holding the rq lock
v7:
* Minor spelling fix and unused argument fixes suggested by
  Metin Kaya
* Switch to curr_selected for consistency, and minor rewording
  of commit message for clarity
* Rename variables selected instead of curr when we're using
  rq_selected()
* Reduce macros in CONFIG_SCHED_PROXY_EXEC ifdef sections,
  as suggested by Metin Kaya
v8:
* Use rq->curr, not rq_selected with task_tick, as suggested by
  Valentin
* Minor rework to reorder this with CONFIG_SCHED_PROXY_EXEC patch
---
 kernel/sched/core.c     | 46 ++++++++++++++++++++++++++---------------
 kernel/sched/deadline.c | 35 ++++++++++++++++---------------
 kernel/sched/fair.c     | 18 ++++++++--------
 kernel/sched/rt.c       | 40 +++++++++++++++++------------------
 kernel/sched/sched.h    | 25 ++++++++++++++++++++--
 5 files changed, 99 insertions(+), 65 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 0eaa0855ef86..3a21f5e903bf 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -794,7 +794,7 @@ static enum hrtimer_restart hrtick(struct hrtimer *timer)
 
 	rq_lock(rq, &rf);
 	update_rq_clock(rq);
-	rq->curr->sched_class->task_tick(rq, rq->curr, 1);
+	rq_selected(rq)->sched_class->task_tick(rq, rq->curr, 1);
 	rq_unlock(rq, &rf);
 
 	return HRTIMER_NORESTART;
@@ -2236,16 +2236,18 @@ static inline void check_class_changed(struct rq *rq, struct task_struct *p,
 
 void wakeup_preempt(struct rq *rq, struct task_struct *p, int flags)
 {
-	if (p->sched_class == rq->curr->sched_class)
-		rq->curr->sched_class->wakeup_preempt(rq, p, flags);
-	else if (sched_class_above(p->sched_class, rq->curr->sched_class))
+	struct task_struct *selected = rq_selected(rq);
+
+	if (p->sched_class == selected->sched_class)
+		selected->sched_class->wakeup_preempt(rq, p, flags);
+	else if (sched_class_above(p->sched_class, selected->sched_class))
 		resched_curr(rq);
 
 	/*
 	 * A queue event has occurred, and we're going to schedule.  In
 	 * this case, we can save a useless back to back clock update.
 	 */
-	if (task_on_rq_queued(rq->curr) && test_tsk_need_resched(rq->curr))
+	if (task_on_rq_queued(selected) && test_tsk_need_resched(rq->curr))
 		rq_clock_skip_update(rq);
 }
 
@@ -2772,7 +2774,7 @@ __do_set_cpus_allowed(struct task_struct *p, struct affinity_context *ctx)
 		lockdep_assert_held(&p->pi_lock);
 
 	queued = task_on_rq_queued(p);
-	running = task_current(rq, p);
+	running = task_current_selected(rq, p);
 
 	if (queued) {
 		/*
@@ -5596,7 +5598,7 @@ unsigned long long task_sched_runtime(struct task_struct *p)
 	 * project cycles that may never be accounted to this
 	 * thread, breaking clock_gettime().
 	 */
-	if (task_current(rq, p) && task_on_rq_queued(p)) {
+	if (task_current_selected(rq, p) && task_on_rq_queued(p)) {
 		prefetch_curr_exec_start(p);
 		update_rq_clock(rq);
 		p->sched_class->update_curr(rq);
@@ -5664,7 +5666,8 @@ void scheduler_tick(void)
 {
 	int cpu = smp_processor_id();
 	struct rq *rq = cpu_rq(cpu);
-	struct task_struct *curr = rq->curr;
+	/* accounting goes to the selected task */
+	struct task_struct *selected;
 	struct rq_flags rf;
 	unsigned long thermal_pressure;
 	u64 resched_latency;
@@ -5675,16 +5678,17 @@ void scheduler_tick(void)
 	sched_clock_tick();
 
 	rq_lock(rq, &rf);
+	selected = rq_selected(rq);
 
 	update_rq_clock(rq);
 	thermal_pressure = arch_scale_thermal_pressure(cpu_of(rq));
 	update_thermal_load_avg(rq_clock_thermal(rq), rq, thermal_pressure);
-	curr->sched_class->task_tick(rq, curr, 0);
+	selected->sched_class->task_tick(rq, selected, 0);
 	if (sched_feat(LATENCY_WARN))
 		resched_latency = cpu_resched_latency(rq);
 	calc_global_load_tick(rq);
 	sched_core_tick(rq);
-	task_tick_mm_cid(rq, curr);
+	task_tick_mm_cid(rq, selected);
 
 	rq_unlock(rq, &rf);
 
@@ -5693,8 +5697,8 @@ void scheduler_tick(void)
 
 	perf_event_task_tick();
 
-	if (curr->flags & PF_WQ_WORKER)
-		wq_worker_tick(curr);
+	if (selected->flags & PF_WQ_WORKER)
+		wq_worker_tick(selected);
 
 #ifdef CONFIG_SMP
 	rq->idle_balance = idle_cpu(cpu);
@@ -5759,6 +5763,12 @@ static void sched_tick_remote(struct work_struct *work)
 		struct task_struct *curr = rq->curr;
 
 		if (cpu_online(cpu)) {
+			/*
+			 * Since this is a remote tick for full dynticks mode,
+			 * we are always sure that there is no proxy (only a
+			 * single task is running).
+			 */
+			SCHED_WARN_ON(rq->curr != rq_selected(rq));
 			update_rq_clock(rq);
 
 			if (!is_idle_task(curr)) {
@@ -6712,6 +6722,7 @@ static void __sched notrace __schedule(unsigned int sched_mode)
 	}
 
 	next = pick_next_task(rq, prev, &rf);
+	rq_set_selected(rq, next);
 	clear_tsk_need_resched(prev);
 	clear_preempt_need_resched();
 #ifdef CONFIG_SCHED_DEBUG
@@ -7222,7 +7233,7 @@ void rt_mutex_setprio(struct task_struct *p, struct task_struct *pi_task)
 
 	prev_class = p->sched_class;
 	queued = task_on_rq_queued(p);
-	running = task_current(rq, p);
+	running = task_current_selected(rq, p);
 	if (queued)
 		dequeue_task(rq, p, queue_flag);
 	if (running)
@@ -7312,7 +7323,7 @@ void set_user_nice(struct task_struct *p, long nice)
 	}
 
 	queued = task_on_rq_queued(p);
-	running = task_current(rq, p);
+	running = task_current_selected(rq, p);
 	if (queued)
 		dequeue_task(rq, p, DEQUEUE_SAVE | DEQUEUE_NOCLOCK);
 	if (running)
@@ -7891,7 +7902,7 @@ static int __sched_setscheduler(struct task_struct *p,
 	}
 
 	queued = task_on_rq_queued(p);
-	running = task_current(rq, p);
+	running = task_current_selected(rq, p);
 	if (queued)
 		dequeue_task(rq, p, queue_flags);
 	if (running)
@@ -9318,6 +9329,7 @@ void __init init_idle(struct task_struct *idle, int cpu)
 	rcu_read_unlock();
 
 	rq->idle = idle;
+	rq_set_selected(rq, idle);
 	rcu_assign_pointer(rq->curr, idle);
 	idle->on_rq = TASK_ON_RQ_QUEUED;
 #ifdef CONFIG_SMP
@@ -9407,7 +9419,7 @@ void sched_setnuma(struct task_struct *p, int nid)
 
 	rq = task_rq_lock(p, &rf);
 	queued = task_on_rq_queued(p);
-	running = task_current(rq, p);
+	running = task_current_selected(rq, p);
 
 	if (queued)
 		dequeue_task(rq, p, DEQUEUE_SAVE);
@@ -10512,7 +10524,7 @@ void sched_move_task(struct task_struct *tsk)
 
 	update_rq_clock(rq);
 
-	running = task_current(rq, tsk);
+	running = task_current_selected(rq, tsk);
 	queued = task_on_rq_queued(tsk);
 
 	if (queued)
diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index 1b9cdb507498..c30b592d6e9d 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -1218,7 +1218,7 @@ static enum hrtimer_restart dl_task_timer(struct hrtimer *timer)
 #endif
 
 	enqueue_task_dl(rq, p, ENQUEUE_REPLENISH);
-	if (dl_task(rq->curr))
+	if (dl_task(rq_selected(rq)))
 		wakeup_preempt_dl(rq, p, 0);
 	else
 		resched_curr(rq);
@@ -1442,7 +1442,7 @@ void dl_server_init(struct sched_dl_entity *dl_se, struct rq *rq,
  */
 static void update_curr_dl(struct rq *rq)
 {
-	struct task_struct *curr = rq->curr;
+	struct task_struct *curr = rq_selected(rq);
 	struct sched_dl_entity *dl_se = &curr->dl;
 	s64 delta_exec;
 
@@ -1899,7 +1899,7 @@ static int find_later_rq(struct task_struct *task);
 static int
 select_task_rq_dl(struct task_struct *p, int cpu, int flags)
 {
-	struct task_struct *curr;
+	struct task_struct *curr, *selected;
 	bool select_rq;
 	struct rq *rq;
 
@@ -1910,6 +1910,7 @@ select_task_rq_dl(struct task_struct *p, int cpu, int flags)
 
 	rcu_read_lock();
 	curr = READ_ONCE(rq->curr); /* unlocked access */
+	selected = READ_ONCE(rq_selected(rq));
 
 	/*
 	 * If we are dealing with a -deadline task, we must
@@ -1920,9 +1921,9 @@ select_task_rq_dl(struct task_struct *p, int cpu, int flags)
 	 * other hand, if it has a shorter deadline, we
 	 * try to make it stay here, it might be important.
 	 */
-	select_rq = unlikely(dl_task(curr)) &&
+	select_rq = unlikely(dl_task(selected)) &&
 		    (curr->nr_cpus_allowed < 2 ||
-		     !dl_entity_preempt(&p->dl, &curr->dl)) &&
+		     !dl_entity_preempt(&p->dl, &selected->dl)) &&
 		    p->nr_cpus_allowed > 1;
 
 	/*
@@ -1985,7 +1986,7 @@ static void check_preempt_equal_dl(struct rq *rq, struct task_struct *p)
 	 * let's hope p can move out.
 	 */
 	if (rq->curr->nr_cpus_allowed == 1 ||
-	    !cpudl_find(&rq->rd->cpudl, rq->curr, NULL))
+	    !cpudl_find(&rq->rd->cpudl, rq_selected(rq), NULL))
 		return;
 
 	/*
@@ -2024,7 +2025,7 @@ static int balance_dl(struct rq *rq, struct task_struct *p, struct rq_flags *rf)
 static void wakeup_preempt_dl(struct rq *rq, struct task_struct *p,
 				  int flags)
 {
-	if (dl_entity_preempt(&p->dl, &rq->curr->dl)) {
+	if (dl_entity_preempt(&p->dl, &rq_selected(rq)->dl)) {
 		resched_curr(rq);
 		return;
 	}
@@ -2034,7 +2035,7 @@ static void wakeup_preempt_dl(struct rq *rq, struct task_struct *p,
 	 * In the unlikely case current and p have the same deadline
 	 * let us try to decide what's the best thing to do...
 	 */
-	if ((p->dl.deadline == rq->curr->dl.deadline) &&
+	if ((p->dl.deadline == rq_selected(rq)->dl.deadline) &&
 	    !test_tsk_need_resched(rq->curr))
 		check_preempt_equal_dl(rq, p);
 #endif /* CONFIG_SMP */
@@ -2066,7 +2067,7 @@ static void set_next_task_dl(struct rq *rq, struct task_struct *p, bool first)
 	if (!first)
 		return;
 
-	if (rq->curr->sched_class != &dl_sched_class)
+	if (rq_selected(rq)->sched_class != &dl_sched_class)
 		update_dl_rq_load_avg(rq_clock_pelt(rq), rq, 0);
 
 	deadline_queue_push_tasks(rq);
@@ -2391,8 +2392,8 @@ static int push_dl_task(struct rq *rq)
 	 * can move away, it makes sense to just reschedule
 	 * without going further in pushing next_task.
 	 */
-	if (dl_task(rq->curr) &&
-	    dl_time_before(next_task->dl.deadline, rq->curr->dl.deadline) &&
+	if (dl_task(rq_selected(rq)) &&
+	    dl_time_before(next_task->dl.deadline, rq_selected(rq)->dl.deadline) &&
 	    rq->curr->nr_cpus_allowed > 1) {
 		resched_curr(rq);
 		return 0;
@@ -2515,7 +2516,7 @@ static void pull_dl_task(struct rq *this_rq)
 			 * deadline than the current task of its runqueue.
 			 */
 			if (dl_time_before(p->dl.deadline,
-					   src_rq->curr->dl.deadline))
+					   rq_selected(src_rq)->dl.deadline))
 				goto skip;
 
 			if (is_migration_disabled(p)) {
@@ -2554,9 +2555,9 @@ static void task_woken_dl(struct rq *rq, struct task_struct *p)
 	if (!task_on_cpu(rq, p) &&
 	    !test_tsk_need_resched(rq->curr) &&
 	    p->nr_cpus_allowed > 1 &&
-	    dl_task(rq->curr) &&
+	    dl_task(rq_selected(rq)) &&
 	    (rq->curr->nr_cpus_allowed < 2 ||
-	     !dl_entity_preempt(&p->dl, &rq->curr->dl))) {
+	     !dl_entity_preempt(&p->dl, &rq_selected(rq)->dl))) {
 		push_dl_tasks(rq);
 	}
 }
@@ -2731,12 +2732,12 @@ static void switched_to_dl(struct rq *rq, struct task_struct *p)
 		return;
 	}
 
-	if (rq->curr != p) {
+	if (rq_selected(rq) != p) {
 #ifdef CONFIG_SMP
 		if (p->nr_cpus_allowed > 1 && rq->dl.overloaded)
 			deadline_queue_push_tasks(rq);
 #endif
-		if (dl_task(rq->curr))
+		if (dl_task(rq_selected(rq)))
 			wakeup_preempt_dl(rq, p, 0);
 		else
 			resched_curr(rq);
@@ -2765,7 +2766,7 @@ static void prio_changed_dl(struct rq *rq, struct task_struct *p,
 	if (!rq->dl.overloaded)
 		deadline_queue_pull_task(rq);
 
-	if (task_current(rq, p)) {
+	if (task_current_selected(rq, p)) {
 		/*
 		 * If we now have a earlier deadline task than p,
 		 * then reschedule, provided p is still on this
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 03be0d1330a6..46f87fd47a33 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1140,7 +1140,7 @@ static inline void update_curr_task(struct task_struct *p, s64 delta_exec)
  */
 s64 update_curr_common(struct rq *rq)
 {
-	struct task_struct *curr = rq->curr;
+	struct task_struct *curr = rq_selected(rq);
 	s64 delta_exec;
 
 	delta_exec = update_curr_se(rq, &curr->se);
@@ -1177,7 +1177,7 @@ static void update_curr(struct cfs_rq *cfs_rq)
 
 static void update_curr_fair(struct rq *rq)
 {
-	update_curr(cfs_rq_of(&rq->curr->se));
+	update_curr(cfs_rq_of(&rq_selected(rq)->se));
 }
 
 static inline void
@@ -6633,7 +6633,7 @@ static void hrtick_start_fair(struct rq *rq, struct task_struct *p)
 		s64 delta = slice - ran;
 
 		if (delta < 0) {
-			if (task_current(rq, p))
+			if (task_current_selected(rq, p))
 				resched_curr(rq);
 			return;
 		}
@@ -6648,7 +6648,7 @@ static void hrtick_start_fair(struct rq *rq, struct task_struct *p)
  */
 static void hrtick_update(struct rq *rq)
 {
-	struct task_struct *curr = rq->curr;
+	struct task_struct *curr = rq_selected(rq);
 
 	if (!hrtick_enabled_fair(rq) || curr->sched_class != &fair_sched_class)
 		return;
@@ -8279,7 +8279,7 @@ static void set_next_buddy(struct sched_entity *se)
  */
 static void check_preempt_wakeup_fair(struct rq *rq, struct task_struct *p, int wake_flags)
 {
-	struct task_struct *curr = rq->curr;
+	struct task_struct *curr = rq_selected(rq);
 	struct sched_entity *se = &curr->se, *pse = &p->se;
 	struct cfs_rq *cfs_rq = task_cfs_rq(curr);
 	int cse_is_idle, pse_is_idle;
@@ -8310,7 +8310,7 @@ static void check_preempt_wakeup_fair(struct rq *rq, struct task_struct *p, int
 	 * prevents us from potentially nominating it as a false LAST_BUDDY
 	 * below.
 	 */
-	if (test_tsk_need_resched(curr))
+	if (test_tsk_need_resched(rq->curr))
 		return;
 
 	/* Idle tasks are by definition preempted by non-idle tasks. */
@@ -9292,7 +9292,7 @@ static bool __update_blocked_others(struct rq *rq, bool *done)
 	 * update_load_avg() can call cpufreq_update_util(). Make sure that RT,
 	 * DL and IRQ signals have been updated before updating CFS.
 	 */
-	curr_class = rq->curr->sched_class;
+	curr_class = rq_selected(rq)->sched_class;
 
 	thermal_pressure = arch_scale_thermal_pressure(cpu_of(rq));
 
@@ -12661,7 +12661,7 @@ prio_changed_fair(struct rq *rq, struct task_struct *p, int oldprio)
 	 * our priority decreased, or if we are not currently running on
 	 * this runqueue and our priority is higher than the current's
 	 */
-	if (task_current(rq, p)) {
+	if (task_current_selected(rq, p)) {
 		if (p->prio > oldprio)
 			resched_curr(rq);
 	} else
@@ -12764,7 +12764,7 @@ static void switched_to_fair(struct rq *rq, struct task_struct *p)
 		 * kick off the schedule if running, otherwise just see
 		 * if we can still preempt the current task.
 		 */
-		if (task_current(rq, p))
+		if (task_current_selected(rq, p))
 			resched_curr(rq);
 		else
 			wakeup_preempt(rq, p, 0);
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 638e7c158ae4..48fc7a198f1a 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -530,7 +530,7 @@ static void dequeue_rt_entity(struct sched_rt_entity *rt_se, unsigned int flags)
 
 static void sched_rt_rq_enqueue(struct rt_rq *rt_rq)
 {
-	struct task_struct *curr = rq_of_rt_rq(rt_rq)->curr;
+	struct task_struct *curr = rq_selected(rq_of_rt_rq(rt_rq));
 	struct rq *rq = rq_of_rt_rq(rt_rq);
 	struct sched_rt_entity *rt_se;
 
@@ -1000,7 +1000,7 @@ static int sched_rt_runtime_exceeded(struct rt_rq *rt_rq)
  */
 static void update_curr_rt(struct rq *rq)
 {
-	struct task_struct *curr = rq->curr;
+	struct task_struct *curr = rq_selected(rq);
 	struct sched_rt_entity *rt_se = &curr->rt;
 	s64 delta_exec;
 
@@ -1543,7 +1543,7 @@ static int find_lowest_rq(struct task_struct *task);
 static int
 select_task_rq_rt(struct task_struct *p, int cpu, int flags)
 {
-	struct task_struct *curr;
+	struct task_struct *curr, *selected;
 	struct rq *rq;
 	bool test;
 
@@ -1555,6 +1555,7 @@ select_task_rq_rt(struct task_struct *p, int cpu, int flags)
 
 	rcu_read_lock();
 	curr = READ_ONCE(rq->curr); /* unlocked access */
+	selected = READ_ONCE(rq_selected(rq));
 
 	/*
 	 * If the current task on @p's runqueue is an RT task, then
@@ -1583,8 +1584,8 @@ select_task_rq_rt(struct task_struct *p, int cpu, int flags)
 	 * systems like big.LITTLE.
 	 */
 	test = curr &&
-	       unlikely(rt_task(curr)) &&
-	       (curr->nr_cpus_allowed < 2 || curr->prio <= p->prio);
+	       unlikely(rt_task(selected)) &&
+	       (curr->nr_cpus_allowed < 2 || selected->prio <= p->prio);
 
 	if (test || !rt_task_fits_capacity(p, cpu)) {
 		int target = find_lowest_rq(p);
@@ -1614,12 +1615,8 @@ select_task_rq_rt(struct task_struct *p, int cpu, int flags)
 
 static void check_preempt_equal_prio(struct rq *rq, struct task_struct *p)
 {
-	/*
-	 * Current can't be migrated, useless to reschedule,
-	 * let's hope p can move out.
-	 */
 	if (rq->curr->nr_cpus_allowed == 1 ||
-	    !cpupri_find(&rq->rd->cpupri, rq->curr, NULL))
+	    !cpupri_find(&rq->rd->cpupri, rq_selected(rq), NULL))
 		return;
 
 	/*
@@ -1662,7 +1659,9 @@ static int balance_rt(struct rq *rq, struct task_struct *p, struct rq_flags *rf)
  */
 static void wakeup_preempt_rt(struct rq *rq, struct task_struct *p, int flags)
 {
-	if (p->prio < rq->curr->prio) {
+	struct task_struct *curr = rq_selected(rq);
+
+	if (p->prio < curr->prio) {
 		resched_curr(rq);
 		return;
 	}
@@ -1680,7 +1679,7 @@ static void wakeup_preempt_rt(struct rq *rq, struct task_struct *p, int flags)
 	 * to move current somewhere else, making room for our non-migratable
 	 * task.
 	 */
-	if (p->prio == rq->curr->prio && !test_tsk_need_resched(rq->curr))
+	if (p->prio == curr->prio && !test_tsk_need_resched(rq->curr))
 		check_preempt_equal_prio(rq, p);
 #endif
 }
@@ -1705,7 +1704,7 @@ static inline void set_next_task_rt(struct rq *rq, struct task_struct *p, bool f
 	 * utilization. We only care of the case where we start to schedule a
 	 * rt task
 	 */
-	if (rq->curr->sched_class != &rt_sched_class)
+	if (rq_selected(rq)->sched_class != &rt_sched_class)
 		update_rt_rq_load_avg(rq_clock_pelt(rq), rq, 0);
 
 	rt_queue_push_tasks(rq);
@@ -1977,6 +1976,7 @@ static struct task_struct *pick_next_pushable_task(struct rq *rq)
 
 	BUG_ON(rq->cpu != task_cpu(p));
 	BUG_ON(task_current(rq, p));
+	BUG_ON(task_current_selected(rq, p));
 	BUG_ON(p->nr_cpus_allowed <= 1);
 
 	BUG_ON(!task_on_rq_queued(p));
@@ -2009,7 +2009,7 @@ static int push_rt_task(struct rq *rq, bool pull)
 	 * higher priority than current. If that's the case
 	 * just reschedule current.
 	 */
-	if (unlikely(next_task->prio < rq->curr->prio)) {
+	if (unlikely(next_task->prio < rq_selected(rq)->prio)) {
 		resched_curr(rq);
 		return 0;
 	}
@@ -2362,7 +2362,7 @@ static void pull_rt_task(struct rq *this_rq)
 			 * p if it is lower in priority than the
 			 * current task on the run queue
 			 */
-			if (p->prio < src_rq->curr->prio)
+			if (p->prio < rq_selected(src_rq)->prio)
 				goto skip;
 
 			if (is_migration_disabled(p)) {
@@ -2404,9 +2404,9 @@ static void task_woken_rt(struct rq *rq, struct task_struct *p)
 	bool need_to_push = !task_on_cpu(rq, p) &&
 			    !test_tsk_need_resched(rq->curr) &&
 			    p->nr_cpus_allowed > 1 &&
-			    (dl_task(rq->curr) || rt_task(rq->curr)) &&
+			    (dl_task(rq_selected(rq)) || rt_task(rq_selected(rq))) &&
 			    (rq->curr->nr_cpus_allowed < 2 ||
-			     rq->curr->prio <= p->prio);
+			     rq_selected(rq)->prio <= p->prio);
 
 	if (need_to_push)
 		push_rt_tasks(rq);
@@ -2490,7 +2490,7 @@ static void switched_to_rt(struct rq *rq, struct task_struct *p)
 		if (p->nr_cpus_allowed > 1 && rq->rt.overloaded)
 			rt_queue_push_tasks(rq);
 #endif /* CONFIG_SMP */
-		if (p->prio < rq->curr->prio && cpu_online(cpu_of(rq)))
+		if (p->prio < rq_selected(rq)->prio && cpu_online(cpu_of(rq)))
 			resched_curr(rq);
 	}
 }
@@ -2505,7 +2505,7 @@ prio_changed_rt(struct rq *rq, struct task_struct *p, int oldprio)
 	if (!task_on_rq_queued(p))
 		return;
 
-	if (task_current(rq, p)) {
+	if (task_current_selected(rq, p)) {
 #ifdef CONFIG_SMP
 		/*
 		 * If our priority decreases while running, we
@@ -2531,7 +2531,7 @@ prio_changed_rt(struct rq *rq, struct task_struct *p, int oldprio)
 		 * greater than the current running task
 		 * then reschedule.
 		 */
-		if (p->prio < rq->curr->prio)
+		if (p->prio < rq_selected(rq)->prio)
 			resched_curr(rq);
 	}
 }
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index f25eec405df9..3c64a875f0ea 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1030,7 +1030,7 @@ struct rq {
 	 */
 	unsigned int		nr_uninterruptible;
 
-	struct task_struct __rcu	*curr;
+	struct task_struct __rcu	*curr;       /* Execution context */
 	struct task_struct	*idle;
 	struct task_struct	*stop;
 	unsigned long		next_balance;
@@ -1225,6 +1225,13 @@ DECLARE_PER_CPU_SHARED_ALIGNED(struct rq, runqueues);
 #define cpu_curr(cpu)		(cpu_rq(cpu)->curr)
 #define raw_rq()		raw_cpu_ptr(&runqueues)
 
+/* For now, rq_selected == rq->curr */
+#define rq_selected(rq)		((rq)->curr)
+static inline void rq_set_selected(struct rq *rq, struct task_struct *t)
+{
+	/* Do nothing */
+}
+
 struct sched_group;
 #ifdef CONFIG_SCHED_CORE
 static inline struct cpumask *sched_group_span(struct sched_group *sg);
@@ -2148,11 +2155,25 @@ static inline u64 global_rt_runtime(void)
 	return (u64)sysctl_sched_rt_runtime * NSEC_PER_USEC;
 }
 
+/*
+ * Is p the current execution context?
+ */
 static inline int task_current(struct rq *rq, struct task_struct *p)
 {
 	return rq->curr == p;
 }
 
+/*
+ * Is p the current scheduling context?
+ *
+ * Note that it might be the current execution context at the same time if
+ * rq->curr == rq_selected() == p.
+ */
+static inline int task_current_selected(struct rq *rq, struct task_struct *p)
+{
+	return rq_selected(rq) == p;
+}
+
 static inline int task_on_cpu(struct rq *rq, struct task_struct *p)
 {
 #ifdef CONFIG_SMP
@@ -2322,7 +2343,7 @@ struct sched_class {
 
 static inline void put_prev_task(struct rq *rq, struct task_struct *prev)
 {
-	WARN_ON_ONCE(rq->curr != prev);
+	WARN_ON_ONCE(rq_selected(rq) != prev);
 	prev->sched_class->put_prev_task(rq, prev);
 }
 
-- 
2.44.0.478.gd926399ef9-goog