mutex.h

 1/* SPDX-License-Identifier: GPL-2.0 */
 2/*
 3 * Mutexes: blocking mutual exclusion locks
 4 *
 5 * started by Ingo Molnar:
 6 *
 7 *  Copyright (C) 2004, 2005, 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
 8 */
 9#ifndef CONFIG_PREEMPT_RT
10/*
11 * This is the control structure for tasks blocked on mutex, which resides
12 * on the blocked task's kernel stack:
13 */
14struct mutex_waiter {
15	struct list_head	list;
16	struct task_struct	*task;
17	struct ww_acquire_ctx	*ww_ctx;
18#ifdef CONFIG_DEBUG_MUTEXES
19	void			*magic;
20#endif
21};
22
23/*
24 * @owner: contains: 'struct task_struct *' to the current lock owner,
25 * NULL means not owned. Since task_struct pointers are aligned at
26 * at least L1_CACHE_BYTES, we have low bits to store extra state.
27 *
28 * Bit0 indicates a non-empty waiter list; unlock must issue a wakeup.
29 * Bit1 indicates unlock needs to hand the lock to the top-waiter
30 * Bit2 indicates handoff has been done and we're waiting for pickup.
31 */
32#define MUTEX_FLAG_WAITERS	0x01
33#define MUTEX_FLAG_HANDOFF	0x02
34#define MUTEX_FLAG_PICKUP	0x04
35
36#define MUTEX_FLAGS		0x07
37
38/*
39 * Internal helper function; C doesn't allow us to hide it :/
40 *
41 * DO NOT USE (outside of mutex & scheduler code).
42 */
43static inline struct task_struct *__mutex_owner(struct mutex *lock)
44{
45	if (!lock)
46		return NULL;
47	return (struct task_struct *)(atomic_long_read(&lock->owner) & ~MUTEX_FLAGS);
48}
49
50#ifdef CONFIG_DEBUG_MUTEXES
51extern void debug_mutex_lock_common(struct mutex *lock,
52				    struct mutex_waiter *waiter);
53extern void debug_mutex_wake_waiter(struct mutex *lock,
54				    struct mutex_waiter *waiter);
55extern void debug_mutex_free_waiter(struct mutex_waiter *waiter);
56extern void debug_mutex_add_waiter(struct mutex *lock,
57				   struct mutex_waiter *waiter,
58				   struct task_struct *task);
59extern void debug_mutex_remove_waiter(struct mutex *lock, struct mutex_waiter *waiter,
60				      struct task_struct *task);
61extern void debug_mutex_unlock(struct mutex *lock);
62extern void debug_mutex_init(struct mutex *lock);
63#else /* CONFIG_DEBUG_MUTEXES */
64# define debug_mutex_lock_common(lock, waiter)		do { } while (0)
65# define debug_mutex_wake_waiter(lock, waiter)		do { } while (0)
66# define debug_mutex_free_waiter(waiter)		do { } while (0)
67# define debug_mutex_add_waiter(lock, waiter, ti)	do { } while (0)
68# define debug_mutex_remove_waiter(lock, waiter, ti)	do { } while (0)
69# define debug_mutex_unlock(lock)			do { } while (0)
70# define debug_mutex_init(lock)				do { } while (0)
71#endif /* !CONFIG_DEBUG_MUTEXES */
72#endif /* CONFIG_PREEMPT_RT */