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Date:   Mon,  6 Nov 2023 19:34:53 +0000
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Subject: [PATCH v6 10/20] locking/mutex: Switch to mutex handoffs for CONFIG_PROXY_EXEC
From:   John Stultz <jstultz@google.com>
To:     LKML <linux-kernel@vger.kernel.org>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        Joel Fernandes <joelaf@google.com>,
        Qais Yousef <qyousef@google.com>,
        Ingo Molnar <mingo@redhat.com>,
        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>, kernel-team@android.com,
        Valentin Schneider <valentin.schneider@arm.com>,
        "Connor O'Brien" <connoro@google.com>,
        John Stultz <jstultz@google.com>
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From: Peter Zijlstra <peterz@infradead.org>

Since with PROXY_EXEC, we will want to hand off locks to the
task's we are running on behalf of, switch to using mutex
handoffs.

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: kernel-team@android.com
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
[rebased, added comments and changelog]
Signed-off-by: Juri Lelli <juri.lelli@redhat.com>
[Fixed rebase conflicts]
[squashed sched: Ensure blocked_on is always guarded by blocked_lock]
Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
[fix rebase conflicts, various fixes & tweaks commented inline]
[squashed sched: Use rq->curr vs rq->proxy checks]
Signed-off-by: Connor O'Brien <connoro@google.com>
[jstultz: Split out only the very basic initial framework
 for proxy logic from a larger patch.]
Signed-off-by: John Stultz <jstultz@google.com>
---
v5:
* Split out from core proxy patch
v6:
* Rework to use sched_proxy_exec() instead of #ifdef CONFIG_PROXY_EXEC
---
 kernel/Kconfig.locks   |  2 +-
 kernel/locking/mutex.c | 39 ++++++++++++++++++++++-----------------
 2 files changed, 23 insertions(+), 18 deletions(-)

diff --git a/kernel/Kconfig.locks b/kernel/Kconfig.locks
index 4198f0273ecd..791c98f1d329 100644
--- a/kernel/Kconfig.locks
+++ b/kernel/Kconfig.locks
@@ -226,7 +226,7 @@ config ARCH_SUPPORTS_ATOMIC_RMW
 
 config MUTEX_SPIN_ON_OWNER
 	def_bool y
-	depends on SMP && ARCH_SUPPORTS_ATOMIC_RMW
+	depends on SMP && ARCH_SUPPORTS_ATOMIC_RMW && !PROXY_EXEC
 
 config RWSEM_SPIN_ON_OWNER
        def_bool y
diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c
index f37b7afe8aa5..5394a3c4b5d9 100644
--- a/kernel/locking/mutex.c
+++ b/kernel/locking/mutex.c
@@ -914,26 +914,31 @@ static noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigne
 
 	mutex_release(&lock->dep_map, ip);
 
-	/*
-	 * Release the lock before (potentially) taking the spinlock such that
-	 * other contenders can get on with things ASAP.
-	 *
-	 * Except when HANDOFF, in that case we must not clear the owner field,
-	 * but instead set it to the top waiter.
-	 */
-	owner = atomic_long_read(&lock->owner);
-	for (;;) {
-		MUTEX_WARN_ON(__owner_task(owner) != current);
-		MUTEX_WARN_ON(owner & MUTEX_FLAG_PICKUP);
-
-		if (owner & MUTEX_FLAG_HANDOFF)
-			break;
+	if (sched_proxy_exec()) {
+		/* Always force HANDOFF for Proxy Exec for now. Revisit. */
+		owner = MUTEX_FLAG_HANDOFF;
+	} else {
+		/*
+		 * Release the lock before (potentially) taking the spinlock
+		 * such that other contenders can get on with things ASAP.
+		 *
+		 * Except when HANDOFF, in that case we must not clear the
+		 * owner field, but instead set it to the top waiter.
+		 */
+		owner = atomic_long_read(&lock->owner);
+		for (;;) {
+			MUTEX_WARN_ON(__owner_task(owner) != current);
+			MUTEX_WARN_ON(owner & MUTEX_FLAG_PICKUP);
 
-		if (atomic_long_try_cmpxchg_release(&lock->owner, &owner, __owner_flags(owner))) {
-			if (owner & MUTEX_FLAG_WAITERS)
+			if (owner & MUTEX_FLAG_HANDOFF)
 				break;
 
-			return;
+			if (atomic_long_try_cmpxchg_release(&lock->owner, &owner,
+							    __owner_flags(owner))) {
+				if (owner & MUTEX_FLAG_WAITERS)
+					break;
+				return;
+			}
 		}
 	}
 
-- 
2.42.0.869.gea05f2083d-goog