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