1/* SPDX-License-Identifier: GPL-2.0 */
2/*
3 * Wound/Wait Mutexes: blocking mutual exclusion locks with deadlock avoidance
4 *
5 * Original mutex implementation started by Ingo Molnar:
6 *
7 * Copyright (C) 2004, 2005, 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
8 *
9 * Wait/Die implementation:
10 * Copyright (C) 2013 Canonical Ltd.
11 * Choice of algorithm:
12 * Copyright (C) 2018 WMWare Inc.
13 *
14 * This file contains the main data structure and API definitions.
15 */
16
17#ifndef __LINUX_WW_MUTEX_H
18#define __LINUX_WW_MUTEX_H
19
20#include <linux/mutex.h>
21
22struct ww_class {
23 atomic_long_t stamp;
24 struct lock_class_key acquire_key;
25 struct lock_class_key mutex_key;
26 const char *acquire_name;
27 const char *mutex_name;
28 unsigned int is_wait_die;
29};
30
31struct ww_acquire_ctx {
32 struct task_struct *task;
33 unsigned long stamp;
34 unsigned int acquired;
35 unsigned short wounded;
36 unsigned short is_wait_die;
37#ifdef CONFIG_DEBUG_MUTEXES
38 unsigned int done_acquire;
39 struct ww_class *ww_class;
40 struct ww_mutex *contending_lock;
41#endif
42#ifdef CONFIG_DEBUG_LOCK_ALLOC
43 struct lockdep_map dep_map;
44#endif
45#ifdef CONFIG_DEBUG_WW_MUTEX_SLOWPATH
46 unsigned int deadlock_inject_interval;
47 unsigned int deadlock_inject_countdown;
48#endif
49};
50
51struct ww_mutex {
52 struct mutex base;
53 struct ww_acquire_ctx *ctx;
54#ifdef CONFIG_DEBUG_MUTEXES
55 struct ww_class *ww_class;
56#endif
57};
58
59#ifdef CONFIG_DEBUG_LOCK_ALLOC
60# define __WW_CLASS_MUTEX_INITIALIZER(lockname, class) \
61 , .ww_class = class
62#else
63# define __WW_CLASS_MUTEX_INITIALIZER(lockname, class)
64#endif
65
66#define __WW_CLASS_INITIALIZER(ww_class, _is_wait_die) \
67 { .stamp = ATOMIC_LONG_INIT(0) \
68 , .acquire_name = #ww_class "_acquire" \
69 , .mutex_name = #ww_class "_mutex" \
70 , .is_wait_die = _is_wait_die }
71
72#define __WW_MUTEX_INITIALIZER(lockname, class) \
73 { .base = __MUTEX_INITIALIZER(lockname.base) \
74 __WW_CLASS_MUTEX_INITIALIZER(lockname, class) }
75
76#define DEFINE_WD_CLASS(classname) \
77 struct ww_class classname = __WW_CLASS_INITIALIZER(classname, 1)
78
79#define DEFINE_WW_CLASS(classname) \
80 struct ww_class classname = __WW_CLASS_INITIALIZER(classname, 0)
81
82#define DEFINE_WW_MUTEX(mutexname, ww_class) \
83 struct ww_mutex mutexname = __WW_MUTEX_INITIALIZER(mutexname, ww_class)
84
85/**
86 * ww_mutex_init - initialize the w/w mutex
87 * @lock: the mutex to be initialized
88 * @ww_class: the w/w class the mutex should belong to
89 *
90 * Initialize the w/w mutex to unlocked state and associate it with the given
91 * class.
92 *
93 * It is not allowed to initialize an already locked mutex.
94 */
95static inline void ww_mutex_init(struct ww_mutex *lock,
96 struct ww_class *ww_class)
97{
98 __mutex_init(&lock->base, ww_class->mutex_name, &ww_class->mutex_key);
99 lock->ctx = NULL;
100#ifdef CONFIG_DEBUG_MUTEXES
101 lock->ww_class = ww_class;
102#endif
103}
104
105/**
106 * ww_acquire_init - initialize a w/w acquire context
107 * @ctx: w/w acquire context to initialize
108 * @ww_class: w/w class of the context
109 *
110 * Initializes an context to acquire multiple mutexes of the given w/w class.
111 *
112 * Context-based w/w mutex acquiring can be done in any order whatsoever within
113 * a given lock class. Deadlocks will be detected and handled with the
114 * wait/die logic.
115 *
116 * Mixing of context-based w/w mutex acquiring and single w/w mutex locking can
117 * result in undetected deadlocks and is so forbidden. Mixing different contexts
118 * for the same w/w class when acquiring mutexes can also result in undetected
119 * deadlocks, and is hence also forbidden. Both types of abuse will be caught by
120 * enabling CONFIG_PROVE_LOCKING.
121 *
122 * Nesting of acquire contexts for _different_ w/w classes is possible, subject
123 * to the usual locking rules between different lock classes.
124 *
125 * An acquire context must be released with ww_acquire_fini by the same task
126 * before the memory is freed. It is recommended to allocate the context itself
127 * on the stack.
128 */
129static inline void ww_acquire_init(struct ww_acquire_ctx *ctx,
130 struct ww_class *ww_class)
131{
132 ctx->task = current;
133 ctx->stamp = atomic_long_inc_return_relaxed(&ww_class->stamp);
134 ctx->acquired = 0;
135 ctx->wounded = false;
136 ctx->is_wait_die = ww_class->is_wait_die;
137#ifdef CONFIG_DEBUG_MUTEXES
138 ctx->ww_class = ww_class;
139 ctx->done_acquire = 0;
140 ctx->contending_lock = NULL;
141#endif
142#ifdef CONFIG_DEBUG_LOCK_ALLOC
143 debug_check_no_locks_freed((void *)ctx, sizeof(*ctx));
144 lockdep_init_map(&ctx->dep_map, ww_class->acquire_name,
145 &ww_class->acquire_key, 0);
146 mutex_acquire(&ctx->dep_map, 0, 0, _RET_IP_);
147#endif
148#ifdef CONFIG_DEBUG_WW_MUTEX_SLOWPATH
149 ctx->deadlock_inject_interval = 1;
150 ctx->deadlock_inject_countdown = ctx->stamp & 0xf;
151#endif
152}
153
154/**
155 * ww_acquire_done - marks the end of the acquire phase
156 * @ctx: the acquire context
157 *
158 * Marks the end of the acquire phase, any further w/w mutex lock calls using
159 * this context are forbidden.
160 *
161 * Calling this function is optional, it is just useful to document w/w mutex
162 * code and clearly designated the acquire phase from actually using the locked
163 * data structures.
164 */
165static inline void ww_acquire_done(struct ww_acquire_ctx *ctx)
166{
167#ifdef CONFIG_DEBUG_MUTEXES
168 lockdep_assert_held(ctx);
169
170 DEBUG_LOCKS_WARN_ON(ctx->done_acquire);
171 ctx->done_acquire = 1;
172#endif
173}
174
175/**
176 * ww_acquire_fini - releases a w/w acquire context
177 * @ctx: the acquire context to free
178 *
179 * Releases a w/w acquire context. This must be called _after_ all acquired w/w
180 * mutexes have been released with ww_mutex_unlock.
181 */
182static inline void ww_acquire_fini(struct ww_acquire_ctx *ctx)
183{
184#ifdef CONFIG_DEBUG_MUTEXES
185 mutex_release(&ctx->dep_map, 0, _THIS_IP_);
186
187 DEBUG_LOCKS_WARN_ON(ctx->acquired);
188 if (!IS_ENABLED(CONFIG_PROVE_LOCKING))
189 /*
190 * lockdep will normally handle this,
191 * but fail without anyway
192 */
193 ctx->done_acquire = 1;
194
195 if (!IS_ENABLED(CONFIG_DEBUG_LOCK_ALLOC))
196 /* ensure ww_acquire_fini will still fail if called twice */
197 ctx->acquired = ~0U;
198#endif
199}
200
201/**
202 * ww_mutex_lock - acquire the w/w mutex
203 * @lock: the mutex to be acquired
204 * @ctx: w/w acquire context, or NULL to acquire only a single lock.
205 *
206 * Lock the w/w mutex exclusively for this task.
207 *
208 * Deadlocks within a given w/w class of locks are detected and handled with the
209 * wait/die algorithm. If the lock isn't immediately available this function
210 * will either sleep until it is (wait case). Or it selects the current context
211 * for backing off by returning -EDEADLK (die case). Trying to acquire the
212 * same lock with the same context twice is also detected and signalled by
213 * returning -EALREADY. Returns 0 if the mutex was successfully acquired.
214 *
215 * In the die case the caller must release all currently held w/w mutexes for
216 * the given context and then wait for this contending lock to be available by
217 * calling ww_mutex_lock_slow. Alternatively callers can opt to not acquire this
218 * lock and proceed with trying to acquire further w/w mutexes (e.g. when
219 * scanning through lru lists trying to free resources).
220 *
221 * The mutex must later on be released by the same task that
222 * acquired it. The task may not exit without first unlocking the mutex. Also,
223 * kernel memory where the mutex resides must not be freed with the mutex still
224 * locked. The mutex must first be initialized (or statically defined) before it
225 * can be locked. memset()-ing the mutex to 0 is not allowed. The mutex must be
226 * of the same w/w lock class as was used to initialize the acquire context.
227 *
228 * A mutex acquired with this function must be released with ww_mutex_unlock.
229 */
230extern int /* __must_check */ ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx);
231
232/**
233 * ww_mutex_lock_interruptible - acquire the w/w mutex, interruptible
234 * @lock: the mutex to be acquired
235 * @ctx: w/w acquire context
236 *
237 * Lock the w/w mutex exclusively for this task.
238 *
239 * Deadlocks within a given w/w class of locks are detected and handled with the
240 * wait/die algorithm. If the lock isn't immediately available this function
241 * will either sleep until it is (wait case). Or it selects the current context
242 * for backing off by returning -EDEADLK (die case). Trying to acquire the
243 * same lock with the same context twice is also detected and signalled by
244 * returning -EALREADY. Returns 0 if the mutex was successfully acquired. If a
245 * signal arrives while waiting for the lock then this function returns -EINTR.
246 *
247 * In the die case the caller must release all currently held w/w mutexes for
248 * the given context and then wait for this contending lock to be available by
249 * calling ww_mutex_lock_slow_interruptible. Alternatively callers can opt to
250 * not acquire this lock and proceed with trying to acquire further w/w mutexes
251 * (e.g. when scanning through lru lists trying to free resources).
252 *
253 * The mutex must later on be released by the same task that
254 * acquired it. The task may not exit without first unlocking the mutex. Also,
255 * kernel memory where the mutex resides must not be freed with the mutex still
256 * locked. The mutex must first be initialized (or statically defined) before it
257 * can be locked. memset()-ing the mutex to 0 is not allowed. The mutex must be
258 * of the same w/w lock class as was used to initialize the acquire context.
259 *
260 * A mutex acquired with this function must be released with ww_mutex_unlock.
261 */
262extern int __must_check ww_mutex_lock_interruptible(struct ww_mutex *lock,
263 struct ww_acquire_ctx *ctx);
264
265/**
266 * ww_mutex_lock_slow - slowpath acquiring of the w/w mutex
267 * @lock: the mutex to be acquired
268 * @ctx: w/w acquire context
269 *
270 * Acquires a w/w mutex with the given context after a die case. This function
271 * will sleep until the lock becomes available.
272 *
273 * The caller must have released all w/w mutexes already acquired with the
274 * context and then call this function on the contended lock.
275 *
276 * Afterwards the caller may continue to (re)acquire the other w/w mutexes it
277 * needs with ww_mutex_lock. Note that the -EALREADY return code from
278 * ww_mutex_lock can be used to avoid locking this contended mutex twice.
279 *
280 * It is forbidden to call this function with any other w/w mutexes associated
281 * with the context held. It is forbidden to call this on anything else than the
282 * contending mutex.
283 *
284 * Note that the slowpath lock acquiring can also be done by calling
285 * ww_mutex_lock directly. This function here is simply to help w/w mutex
286 * locking code readability by clearly denoting the slowpath.
287 */
288static inline void
289ww_mutex_lock_slow(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
290{
291 int ret;
292#ifdef CONFIG_DEBUG_MUTEXES
293 DEBUG_LOCKS_WARN_ON(!ctx->contending_lock);
294#endif
295 ret = ww_mutex_lock(lock, ctx);
296 (void)ret;
297}
298
299/**
300 * ww_mutex_lock_slow_interruptible - slowpath acquiring of the w/w mutex, interruptible
301 * @lock: the mutex to be acquired
302 * @ctx: w/w acquire context
303 *
304 * Acquires a w/w mutex with the given context after a die case. This function
305 * will sleep until the lock becomes available and returns 0 when the lock has
306 * been acquired. If a signal arrives while waiting for the lock then this
307 * function returns -EINTR.
308 *
309 * The caller must have released all w/w mutexes already acquired with the
310 * context and then call this function on the contended lock.
311 *
312 * Afterwards the caller may continue to (re)acquire the other w/w mutexes it
313 * needs with ww_mutex_lock. Note that the -EALREADY return code from
314 * ww_mutex_lock can be used to avoid locking this contended mutex twice.
315 *
316 * It is forbidden to call this function with any other w/w mutexes associated
317 * with the given context held. It is forbidden to call this on anything else
318 * than the contending mutex.
319 *
320 * Note that the slowpath lock acquiring can also be done by calling
321 * ww_mutex_lock_interruptible directly. This function here is simply to help
322 * w/w mutex locking code readability by clearly denoting the slowpath.
323 */
324static inline int __must_check
325ww_mutex_lock_slow_interruptible(struct ww_mutex *lock,
326 struct ww_acquire_ctx *ctx)
327{
328#ifdef CONFIG_DEBUG_MUTEXES
329 DEBUG_LOCKS_WARN_ON(!ctx->contending_lock);
330#endif
331 return ww_mutex_lock_interruptible(lock, ctx);
332}
333
334extern void ww_mutex_unlock(struct ww_mutex *lock);
335
336/**
337 * ww_mutex_trylock - tries to acquire the w/w mutex without acquire context
338 * @lock: mutex to lock
339 *
340 * Trylocks a mutex without acquire context, so no deadlock detection is
341 * possible. Returns 1 if the mutex has been acquired successfully, 0 otherwise.
342 */
343static inline int __must_check ww_mutex_trylock(struct ww_mutex *lock)
344{
345 return mutex_trylock(&lock->base);
346}
347
348/***
349 * ww_mutex_destroy - mark a w/w mutex unusable
350 * @lock: the mutex to be destroyed
351 *
352 * This function marks the mutex uninitialized, and any subsequent
353 * use of the mutex is forbidden. The mutex must not be locked when
354 * this function is called.
355 */
356static inline void ww_mutex_destroy(struct ww_mutex *lock)
357{
358 mutex_destroy(&lock->base);
359}
360
361/**
362 * ww_mutex_is_locked - is the w/w mutex locked
363 * @lock: the mutex to be queried
364 *
365 * Returns 1 if the mutex is locked, 0 if unlocked.
366 */
367static inline bool ww_mutex_is_locked(struct ww_mutex *lock)
368{
369 return mutex_is_locked(&lock->base);
370}
371
372#endif
373