1 /* SPDX-License-Identifier: GPL-2.0 */
2 /*
3  * RT Mutexes: blocking mutual exclusion locks with PI support
4  *
5  * started by Ingo Molnar and Thomas Gleixner:
6  *
7  *  Copyright (C) 2004-2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
8  *  Copyright (C) 2006, Timesys Corp., Thomas Gleixner <tglx@timesys.com>
9  *
10  * This file contains the private data structure and API definitions.
11  */
12 
13 #ifndef __KERNEL_RTMUTEX_COMMON_H
14 #define __KERNEL_RTMUTEX_COMMON_H
15 
16 #include <linux/debug_locks.h>
17 #include <linux/rtmutex.h>
18 #include <linux/sched/wake_q.h>
19 
20 
21 /*
22  * This is a helper for the struct rt_mutex_waiter below. A waiter goes in two
23  * separate trees and they need their own copy of the sort keys because of
24  * different locking requirements.
25  *
26  * @entry:		rbtree node to enqueue into the waiters tree
27  * @prio:		Priority of the waiter
28  * @deadline:		Deadline of the waiter if applicable
29  *
30  * See rt_waiter_node_less() and waiter_*_prio().
31  */
32 struct rt_waiter_node {
33 	struct rb_node	entry;
34 	int		prio;
35 	u64		deadline;
36 };
37 
38 /*
39  * This is the control structure for tasks blocked on a rt_mutex,
40  * which is allocated on the kernel stack on of the blocked task.
41  *
42  * @tree:		node to enqueue into the mutex waiters tree
43  * @pi_tree:		node to enqueue into the mutex owner waiters tree
44  * @task:		task reference to the blocked task
45  * @lock:		Pointer to the rt_mutex on which the waiter blocks
46  * @wake_state:		Wakeup state to use (TASK_NORMAL or TASK_RTLOCK_WAIT)
47  * @ww_ctx:		WW context pointer
48  *
49  * @tree is ordered by @lock->wait_lock
50  * @pi_tree is ordered by rt_mutex_owner(@lock)->pi_lock
51  */
52 struct rt_mutex_waiter {
53 	struct rt_waiter_node	tree;
54 	struct rt_waiter_node	pi_tree;
55 	struct task_struct	*task;
56 	struct rt_mutex_base	*lock;
57 	unsigned int		wake_state;
58 	struct ww_acquire_ctx	*ww_ctx;
59 };
60 
61 /**
62  * rt_wake_q_head - Wrapper around regular wake_q_head to support
63  *		    "sleeping" spinlocks on RT
64  * @head:		The regular wake_q_head for sleeping lock variants
65  * @rtlock_task:	Task pointer for RT lock (spin/rwlock) wakeups
66  */
67 struct rt_wake_q_head {
68 	struct wake_q_head	head;
69 	struct task_struct	*rtlock_task;
70 };
71 
72 #define DEFINE_RT_WAKE_Q(name)						\
73 	struct rt_wake_q_head name = {					\
74 		.head		= WAKE_Q_HEAD_INITIALIZER(name.head),	\
75 		.rtlock_task	= NULL,					\
76 	}
77 
78 /*
79  * PI-futex support (proxy locking functions, etc.):
80  */
81 extern void rt_mutex_init_proxy_locked(struct rt_mutex_base *lock,
82 				       struct task_struct *proxy_owner);
83 extern void rt_mutex_proxy_unlock(struct rt_mutex_base *lock);
84 extern int __rt_mutex_start_proxy_lock(struct rt_mutex_base *lock,
85 				     struct rt_mutex_waiter *waiter,
86 				     struct task_struct *task);
87 extern int rt_mutex_start_proxy_lock(struct rt_mutex_base *lock,
88 				     struct rt_mutex_waiter *waiter,
89 				     struct task_struct *task);
90 extern int rt_mutex_wait_proxy_lock(struct rt_mutex_base *lock,
91 			       struct hrtimer_sleeper *to,
92 			       struct rt_mutex_waiter *waiter);
93 extern bool rt_mutex_cleanup_proxy_lock(struct rt_mutex_base *lock,
94 				 struct rt_mutex_waiter *waiter);
95 
96 extern int rt_mutex_futex_trylock(struct rt_mutex_base *l);
97 extern int __rt_mutex_futex_trylock(struct rt_mutex_base *l);
98 
99 extern void rt_mutex_futex_unlock(struct rt_mutex_base *lock);
100 extern bool __rt_mutex_futex_unlock(struct rt_mutex_base *lock,
101 				struct rt_wake_q_head *wqh);
102 
103 extern void rt_mutex_postunlock(struct rt_wake_q_head *wqh);
104 
105 /*
106  * Must be guarded because this header is included from rcu/tree_plugin.h
107  * unconditionally.
108  */
109 #ifdef CONFIG_RT_MUTEXES
110 static inline int rt_mutex_has_waiters(struct rt_mutex_base *lock)
111 {
112 	return !RB_EMPTY_ROOT(&lock->waiters.rb_root);
113 }
114 
115 /*
116  * Lockless speculative check whether @waiter is still the top waiter on
117  * @lock. This is solely comparing pointers and not derefencing the
118  * leftmost entry which might be about to vanish.
119  */
120 static inline bool rt_mutex_waiter_is_top_waiter(struct rt_mutex_base *lock,
121 						 struct rt_mutex_waiter *waiter)
122 {
123 	struct rb_node *leftmost = rb_first_cached(&lock->waiters);
124 
125 	return rb_entry(leftmost, struct rt_mutex_waiter, tree.entry) == waiter;
126 }
127 
128 static inline struct rt_mutex_waiter *rt_mutex_top_waiter(struct rt_mutex_base *lock)
129 {
130 	struct rb_node *leftmost = rb_first_cached(&lock->waiters);
131 	struct rt_mutex_waiter *w = NULL;
132 
133 	lockdep_assert_held(&lock->wait_lock);
134 
135 	if (leftmost) {
136 		w = rb_entry(leftmost, struct rt_mutex_waiter, tree.entry);
137 		BUG_ON(w->lock != lock);
138 	}
139 	return w;
140 }
141 
142 static inline int task_has_pi_waiters(struct task_struct *p)
143 {
144 	return !RB_EMPTY_ROOT(&p->pi_waiters.rb_root);
145 }
146 
147 static inline struct rt_mutex_waiter *task_top_pi_waiter(struct task_struct *p)
148 {
149 	lockdep_assert_held(&p->pi_lock);
150 
151 	return rb_entry(p->pi_waiters.rb_leftmost, struct rt_mutex_waiter,
152 			pi_tree.entry);
153 }
154 
155 #define RT_MUTEX_HAS_WAITERS	1UL
156 
157 static inline struct task_struct *rt_mutex_owner(struct rt_mutex_base *lock)
158 {
159 	unsigned long owner = (unsigned long) READ_ONCE(lock->owner);
160 
161 	return (struct task_struct *) (owner & ~RT_MUTEX_HAS_WAITERS);
162 }
163 
164 /*
165  * Constants for rt mutex functions which have a selectable deadlock
166  * detection.
167  *
168  * RT_MUTEX_MIN_CHAINWALK:	Stops the lock chain walk when there are
169  *				no further PI adjustments to be made.
170  *
171  * RT_MUTEX_FULL_CHAINWALK:	Invoke deadlock detection with a full
172  *				walk of the lock chain.
173  */
174 enum rtmutex_chainwalk {
175 	RT_MUTEX_MIN_CHAINWALK,
176 	RT_MUTEX_FULL_CHAINWALK,
177 };
178 
179 static inline void __rt_mutex_base_init(struct rt_mutex_base *lock)
180 {
181 	raw_spin_lock_init(&lock->wait_lock);
182 	lock->waiters = RB_ROOT_CACHED;
183 	lock->owner = NULL;
184 }
185 
186 /* Debug functions */
187 static inline void debug_rt_mutex_unlock(struct rt_mutex_base *lock)
188 {
189 	if (IS_ENABLED(CONFIG_DEBUG_RT_MUTEXES))
190 		DEBUG_LOCKS_WARN_ON(rt_mutex_owner(lock) != current);
191 }
192 
193 static inline void debug_rt_mutex_proxy_unlock(struct rt_mutex_base *lock)
194 {
195 	if (IS_ENABLED(CONFIG_DEBUG_RT_MUTEXES))
196 		DEBUG_LOCKS_WARN_ON(!rt_mutex_owner(lock));
197 }
198 
199 static inline void debug_rt_mutex_init_waiter(struct rt_mutex_waiter *waiter)
200 {
201 	if (IS_ENABLED(CONFIG_DEBUG_RT_MUTEXES))
202 		memset(waiter, 0x11, sizeof(*waiter));
203 }
204 
205 static inline void debug_rt_mutex_free_waiter(struct rt_mutex_waiter *waiter)
206 {
207 	if (IS_ENABLED(CONFIG_DEBUG_RT_MUTEXES))
208 		memset(waiter, 0x22, sizeof(*waiter));
209 }
210 
211 static inline void rt_mutex_init_waiter(struct rt_mutex_waiter *waiter)
212 {
213 	debug_rt_mutex_init_waiter(waiter);
214 	RB_CLEAR_NODE(&waiter->pi_tree.entry);
215 	RB_CLEAR_NODE(&waiter->tree.entry);
216 	waiter->wake_state = TASK_NORMAL;
217 	waiter->task = NULL;
218 }
219 
220 static inline void rt_mutex_init_rtlock_waiter(struct rt_mutex_waiter *waiter)
221 {
222 	rt_mutex_init_waiter(waiter);
223 	waiter->wake_state = TASK_RTLOCK_WAIT;
224 }
225 
226 #else /* CONFIG_RT_MUTEXES */
227 /* Used in rcu/tree_plugin.h */
228 static inline struct task_struct *rt_mutex_owner(struct rt_mutex_base *lock)
229 {
230 	return NULL;
231 }
232 #endif  /* !CONFIG_RT_MUTEXES */
233 
234 #endif
235