linux-kernel - [PATCH v4 06/13] locking/mutex: Expose __mutex

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Date:   Thu,  1 Jun 2023 05:58:09 +0000
From:   John Stultz <jstultz@...gle.com>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     Juri Lelli <juri.lelli@...hat.com>,
        Joel Fernandes <joelaf@...gle.com>,
        Qais Yousef <qyousef@...gle.com>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Valentin Schneider <vschneid@...hat.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>,
        Zimuzo Ezeozue <zezeozue@...gle.com>,
        Youssef Esmat <youssefesmat@...gle.com>,
        Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Will Deacon <will@...nel.org>,
        Waiman Long <longman@...hat.com>,
        Boqun Feng <boqun.feng@...il.com>,
        "Paul E . McKenney" <paulmck@...nel.org>, kernel-team@...roid.com,
        Valentin Schneider <valentin.schneider@....com>,
        "Connor O'Brien" <connoro@...gle.com>,
        John Stultz <jstultz@...gle.com>
Subject: [PATCH v4 06/13] locking/mutex: Expose __mutex_owner()

From: Juri Lelli <juri.lelli@...hat.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@...gle.com>
Cc: Qais Yousef <qyousef@...gle.com>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Juri Lelli <juri.lelli@...hat.com>
Cc: Vincent Guittot <vincent.guittot@...aro.org>
Cc: Dietmar Eggemann <dietmar.eggemann@....com>
Cc: Valentin Schneider <vschneid@...hat.com>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Ben Segall <bsegall@...gle.com>
Cc: Zimuzo Ezeozue <zezeozue@...gle.com>
Cc: Youssef Esmat <youssefesmat@...gle.com>
Cc: Mel Gorman <mgorman@...e.de>
Cc: Daniel Bristot de Oliveira <bristot@...hat.com>
Cc: Will Deacon <will@...nel.org>
Cc: Waiman Long <longman@...hat.com>
Cc: Boqun Feng <boqun.feng@...il.com>
Cc: "Paul E . McKenney" <paulmck@...nel.org>
Cc: kernel-team@...roid.com
Signed-off-by: Juri Lelli <juri.lelli@...hat.com>
[Removed the EXPORT_SYMBOL]
Signed-off-by: Valentin Schneider <valentin.schneider@....com>
Signed-off-by: Connor O'Brien <connoro@...gle.com>
[jstultz: Reworked per Peter's suggestions]
Signed-off-by: John Stultz <jstultz@...gle.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 ac3d2e350fac..8c9f9dffe473 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);
-- 
2.41.0.rc0.172.g3f132b7071-goog