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Date: Tue, 19 Dec 2023 16:18:32 -0800
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Subject: [PATCH v7 21/23] sched: Add find_exec_ctx helper
From: John Stultz <jstultz@google.com>
To: LKML <linux-kernel@vger.kernel.org>
Cc: "Connor O'Brien" <connoro@google.com>, Joel Fernandes <joelaf@google.com>, 
	Qais Yousef <qyousef@google.com>, Ingo Molnar <mingo@redhat.com>, 
	Peter Zijlstra <peterz@infradead.org>, Juri Lelli <juri.lelli@redhat.com>, 
	Vincent Guittot <vincent.guittot@linaro.org>, Dietmar Eggemann <dietmar.eggemann@arm.com>, 
	Valentin Schneider <vschneid@redhat.com>, Steven Rostedt <rostedt@goodmis.org>, 
	Ben Segall <bsegall@google.com>, Zimuzo Ezeozue <zezeozue@google.com>, 
	Youssef Esmat <youssefesmat@google.com>, Mel Gorman <mgorman@suse.de>, 
	Daniel Bristot de Oliveira <bristot@redhat.com>, Will Deacon <will@kernel.org>, Waiman Long <longman@redhat.com>, 
	Boqun Feng <boqun.feng@gmail.com>, "Paul E. McKenney" <paulmck@kernel.org>, 
	Metin Kaya <Metin.Kaya@arm.com>, Xuewen Yan <xuewen.yan94@gmail.com>, 
	K Prateek Nayak <kprateek.nayak@amd.com>, Thomas Gleixner <tglx@linutronix.de>, kernel-team@android.com, 
	John Stultz <jstultz@google.com>
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From: Connor O'Brien <connoro@google.com>

Add a helper to find the runnable owner down a chain of blocked waiters

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
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>
---
 kernel/sched/core.c     | 42 +++++++++++++++++++++++++++++++++++++++++
 kernel/sched/cpupri.c   | 11 ++++++++---
 kernel/sched/deadline.c | 15 +++++++++++++--
 kernel/sched/rt.c       |  9 ++++++++-
 kernel/sched/sched.h    | 10 ++++++++++
 5 files changed, 81 insertions(+), 6 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 0c212dcd4b7a..77a79d5f829a 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3896,6 +3896,48 @@ static void activate_blocked_entities(struct rq *target_rq,
 	}
 	raw_spin_unlock_irqrestore(&owner->blocked_lock, flags);
 }
+
+static inline bool task_queued_on_rq(struct rq *rq, struct task_struct *task)
+{
+	if (!task_on_rq_queued(task))
+		return false;
+	smp_rmb();
+	if (task_rq(task) != rq)
+		return false;
+	smp_rmb();
+	if (!task_on_rq_queued(task))
+		return false;
+	return true;
+}
+
+/*
+ * Returns the unblocked task at the end of the blocked chain starting with p
+ * if that chain is composed entirely of tasks enqueued on rq, or NULL otherwise.
+ */
+struct task_struct *find_exec_ctx(struct rq *rq, struct task_struct *p)
+{
+	struct task_struct *exec_ctx, *owner;
+	struct mutex *mutex;
+
+	if (!sched_proxy_exec())
+		return p;
+
+	lockdep_assert_rq_held(rq);
+
+	for (exec_ctx = p; task_is_blocked(exec_ctx) && !task_on_cpu(rq, exec_ctx);
+							exec_ctx = owner) {
+		mutex = exec_ctx->blocked_on;
+		owner = __mutex_owner(mutex);
+		if (owner == exec_ctx)
+			break;
+
+		if (!task_queued_on_rq(rq, owner) || task_current_selected(rq, owner)) {
+			exec_ctx = NULL;
+			break;
+		}
+	}
+	return exec_ctx;
+}
 #else /* !CONFIG_SCHED_PROXY_EXEC */
 static inline void do_activate_task(struct rq *rq, struct task_struct *p,
 				    int en_flags)
diff --git a/kernel/sched/cpupri.c b/kernel/sched/cpupri.c
index 15e947a3ded7..53be78afdd07 100644
--- a/kernel/sched/cpupri.c
+++ b/kernel/sched/cpupri.c
@@ -96,12 +96,17 @@ static inline int __cpupri_find(struct cpupri *cp, struct task_struct *p,
 	if (skip)
 		return 0;
 
-	if (cpumask_any_and(&p->cpus_mask, vec->mask) >= nr_cpu_ids)
+	if ((p && cpumask_any_and(&p->cpus_mask, vec->mask) >= nr_cpu_ids) ||
+	    (!p && cpumask_any(vec->mask) >= nr_cpu_ids))
 		return 0;
 
 	if (lowest_mask) {
-		cpumask_and(lowest_mask, &p->cpus_mask, vec->mask);
-		cpumask_and(lowest_mask, lowest_mask, cpu_active_mask);
+		if (p) {
+			cpumask_and(lowest_mask, &p->cpus_mask, vec->mask);
+			cpumask_and(lowest_mask, lowest_mask, cpu_active_mask);
+		} else {
+			cpumask_copy(lowest_mask, vec->mask);
+		}
 
 		/*
 		 * We have to ensure that we have at least one bit
diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index 999bd17f11c4..21e56ac58e32 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -1866,6 +1866,8 @@ static void migrate_task_rq_dl(struct task_struct *p, int new_cpu __maybe_unused
 
 static void check_preempt_equal_dl(struct rq *rq, struct task_struct *p)
 {
+	struct task_struct *exec_ctx;
+
 	/*
 	 * Current can't be migrated, useless to reschedule,
 	 * let's hope p can move out.
@@ -1874,12 +1876,16 @@ static void check_preempt_equal_dl(struct rq *rq, struct task_struct *p)
 	    !cpudl_find(&rq->rd->cpudl, rq_selected(rq), rq->curr, NULL))
 		return;
 
+	exec_ctx = find_exec_ctx(rq, p);
+	if (task_current(rq, exec_ctx))
+		return;
+
 	/*
 	 * p is migratable, so let's not schedule it and
 	 * see if it is pushed or pulled somewhere else.
 	 */
 	if (p->nr_cpus_allowed != 1 &&
-	    cpudl_find(&rq->rd->cpudl, p, p, NULL))
+	    cpudl_find(&rq->rd->cpudl, p, exec_ctx, NULL))
 		return;
 
 	resched_curr(rq);
@@ -2169,12 +2175,17 @@ static int find_later_rq(struct task_struct *sched_ctx, struct task_struct *exec
 /* Locks the rq it finds */
 static struct rq *find_lock_later_rq(struct task_struct *task, struct rq *rq)
 {
+	struct task_struct *exec_ctx;
 	struct rq *later_rq = NULL;
 	int tries;
 	int cpu;
 
 	for (tries = 0; tries < DL_MAX_TRIES; tries++) {
-		cpu = find_later_rq(task, task);
+		exec_ctx = find_exec_ctx(rq, task);
+		if (!exec_ctx)
+			break;
+
+		cpu = find_later_rq(task, exec_ctx);
 
 		if ((cpu == -1) || (cpu == rq->cpu))
 			break;
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 6371b0fca4ad..f8134d062fa3 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -1640,6 +1640,11 @@ static void check_preempt_equal_prio(struct rq *rq, struct task_struct *p)
 	    !cpupri_find(&rq->rd->cpupri, rq_selected(rq), rq->curr, NULL))
 		return;
 
+	/* No reason to preempt since rq->curr wouldn't change anyway */
+	exec_ctx = find_exec_ctx(rq, p);
+	if (task_current(rq, exec_ctx))
+		return;
+
 	/*
 	 * p is migratable, so let's not schedule it and
 	 * see if it is pushed or pulled somewhere else.
@@ -1933,12 +1938,14 @@ static int find_lowest_rq(struct task_struct *sched_ctx, struct task_struct *exe
 /* Will lock the rq it finds */
 static struct rq *find_lock_lowest_rq(struct task_struct *task, struct rq *rq)
 {
+	struct task_struct *exec_ctx;
 	struct rq *lowest_rq = NULL;
 	int tries;
 	int cpu;
 
 	for (tries = 0; tries < RT_MAX_TRIES; tries++) {
-		cpu = find_lowest_rq(task, task);
+		exec_ctx = find_exec_ctx(rq, task);
+		cpu = find_lowest_rq(task, exec_ctx);
 
 		if ((cpu == -1) || (cpu == rq->cpu))
 			break;
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index ef3d327e267c..6cd473224cfe 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -3564,6 +3564,16 @@ int task_is_pushable(struct rq *rq, struct task_struct *p, int cpu)
 
 	return 0;
 }
+
+#ifdef CONFIG_SCHED_PROXY_EXEC
+struct task_struct *find_exec_ctx(struct rq *rq, struct task_struct *p);
+#else /* !CONFIG_SCHED_PROXY_EXEC */
+static inline
+struct task_struct *find_exec_ctx(struct rq *rq, struct task_struct *p)
+{
+	return p;
+}
+#endif /* CONFIG_SCHED_PROXY_EXEC */
 #endif
 
 #endif /* _KERNEL_SCHED_SCHED_H */
-- 
2.43.0.472.g3155946c3a-goog