Commit 3a9320ec authored by Juri Lelli's avatar Juri Lelli Committed by Peter Zijlstra
Browse files

locking/mutex: Expose __mutex_owner() 



Implementing proxy execution requires that scheduler code be able to
identify the current owner of a mutex. Expose __mutex_owner() for
this purpose (alone!). Includes a null mutex check, so that users
of the function can be simplified.

[Removed the EXPORT_SYMBOL]
[jstultz: Reworked per Peter's suggestions]
Signed-off-by: default avatarJuri Lelli <juri.lelli@redhat.com>
Signed-off-by: default avatarValentin Schneider <valentin.schneider@arm.com>
Signed-off-by: default avatarConnor O'Brien <connoro@google.com>
Signed-off-by: default avatarJohn Stultz <jstultz@google.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: default avatarMetin Kaya <metin.kaya@arm.com>
Reviewed-by: default avatarValentin Schneider <vschneid@redhat.com>
Tested-by: default avatarK Prateek Nayak <kprateek.nayak@amd.com>
Tested-by: default avatarMetin Kaya <metin.kaya@arm.com>
Link: https://lore.kernel.org/r/20241009235352.1614323-4-jstultz@google.com
parent 5ec58525

kernel/locking/mutex.c

+0 −25
Original line number Diff line number Diff line
@@ -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);

kernel/locking/mutex.h

+27 −0
Original line number Diff line number Diff line
@@ -20,6 +20,33 @@ 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)

{

	if (!lock)

		return NULL;

	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);