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
38struct 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
47struct 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
55struct 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 /**
69 * @first_lock_dep_map: fake lockdep_map for first locked ww_mutex.
70 *
71 * lockdep requires the lockdep_map for the first locked ww_mutex
72 * in a ww transaction to remain in memory until all ww_mutexes of
73 * the transaction have been unlocked. Ensure this by keeping a
74 * fake locked ww_mutex lockdep map between ww_acquire_init() and
75 * ww_acquire_fini().
76 */
77 struct lockdep_map first_lock_dep_map;
78#endif
79#ifdef CONFIG_DEBUG_WW_MUTEX_SLOWPATH
80 unsigned int deadlock_inject_interval;
81 unsigned int deadlock_inject_countdown;
82#endif
83};
84
85#define __WW_CLASS_INITIALIZER(ww_class, _is_wait_die) \
86 { .stamp = ATOMIC_LONG_INIT(0) \
87 , .acquire_name = #ww_class "_acquire" \
88 , .mutex_name = #ww_class "_mutex" \
89 , .is_wait_die = _is_wait_die }
90
91#define DEFINE_WD_CLASS(classname) \
92 struct ww_class classname = __WW_CLASS_INITIALIZER(classname, 1)
93
94#define DEFINE_WW_CLASS(classname) \
95 struct ww_class classname = __WW_CLASS_INITIALIZER(classname, 0)
96
97/**
98 * ww_mutex_init - initialize the w/w mutex
99 * @lock: the mutex to be initialized
100 * @ww_class: the w/w class the mutex should belong to
101 *
102 * Initialize the w/w mutex to unlocked state and associate it with the given
103 * class. Static define macro for w/w mutex is not provided and this function
104 * is the only way to properly initialize the w/w mutex.
105 *
106 * It is not allowed to initialize an already locked mutex.
107 */
108static inline void ww_mutex_init(struct ww_mutex *lock,
109 struct ww_class *ww_class)
110{
111 ww_mutex_base_init(&lock->base, ww_class->mutex_name, &ww_class->mutex_key);
112 lock->ctx = NULL;
113#ifdef DEBUG_WW_MUTEXES
114 lock->ww_class = ww_class;
115#endif
116}
117
118/**
119 * ww_acquire_init - initialize a w/w acquire context
120 * @ctx: w/w acquire context to initialize
121 * @ww_class: w/w class of the context
122 *
123 * Initializes an context to acquire multiple mutexes of the given w/w class.
124 *
125 * Context-based w/w mutex acquiring can be done in any order whatsoever within
126 * a given lock class. Deadlocks will be detected and handled with the
127 * wait/die logic.
128 *
129 * Mixing of context-based w/w mutex acquiring and single w/w mutex locking can
130 * result in undetected deadlocks and is so forbidden. Mixing different contexts
131 * for the same w/w class when acquiring mutexes can also result in undetected
132 * deadlocks, and is hence also forbidden. Both types of abuse will be caught by
133 * enabling CONFIG_PROVE_LOCKING.
134 *
135 * Nesting of acquire contexts for _different_ w/w classes is possible, subject
136 * to the usual locking rules between different lock classes.
137 *
138 * An acquire context must be released with ww_acquire_fini by the same task
139 * before the memory is freed. It is recommended to allocate the context itself
140 * on the stack.
141 */
142static inline void ww_acquire_init(struct ww_acquire_ctx *ctx,
143 struct ww_class *ww_class)
144{
145 ctx->task = current;
146 ctx->stamp = atomic_long_inc_return_relaxed(v: &ww_class->stamp);
147 ctx->acquired = 0;
148 ctx->wounded = false;
149 ctx->is_wait_die = ww_class->is_wait_die;
150#ifdef DEBUG_WW_MUTEXES
151 ctx->ww_class = ww_class;
152 ctx->done_acquire = 0;
153 ctx->contending_lock = NULL;
154#endif
155#ifdef CONFIG_DEBUG_LOCK_ALLOC
156 debug_check_no_locks_freed((void *)ctx, sizeof(*ctx));
157 lockdep_init_map(&ctx->dep_map, ww_class->acquire_name,
158 &ww_class->acquire_key, 0);
159 lockdep_init_map_wait(&ctx->first_lock_dep_map, ww_class->mutex_name,
160 &ww_class->mutex_key, 0, LD_WAIT_SLEEP);
161 mutex_acquire(&ctx->dep_map, 0, 0, _RET_IP_);
162 mutex_acquire_nest(&ctx->first_lock_dep_map, 0, 0, &ctx->dep_map, _RET_IP_);
163#endif
164#ifdef CONFIG_DEBUG_WW_MUTEX_SLOWPATH
165 ctx->deadlock_inject_interval = 1;
166 ctx->deadlock_inject_countdown = ctx->stamp & 0xf;
167#endif
168}
169
170/**
171 * ww_acquire_done - marks the end of the acquire phase
172 * @ctx: the acquire context
173 *
174 * Marks the end of the acquire phase, any further w/w mutex lock calls using
175 * this context are forbidden.
176 *
177 * Calling this function is optional, it is just useful to document w/w mutex
178 * code and clearly designated the acquire phase from actually using the locked
179 * data structures.
180 */
181static inline void ww_acquire_done(struct ww_acquire_ctx *ctx)
182{
183#ifdef DEBUG_WW_MUTEXES
184 lockdep_assert_held(ctx);
185
186 DEBUG_LOCKS_WARN_ON(ctx->done_acquire);
187 ctx->done_acquire = 1;
188#endif
189}
190
191/**
192 * ww_acquire_fini - releases a w/w acquire context
193 * @ctx: the acquire context to free
194 *
195 * Releases a w/w acquire context. This must be called _after_ all acquired w/w
196 * mutexes have been released with ww_mutex_unlock.
197 */
198static inline void ww_acquire_fini(struct ww_acquire_ctx *ctx)
199{
200#ifdef CONFIG_DEBUG_LOCK_ALLOC
201 mutex_release(&ctx->first_lock_dep_map, _THIS_IP_);
202 mutex_release(&ctx->dep_map, _THIS_IP_);
203#endif
204#ifdef DEBUG_WW_MUTEXES
205 DEBUG_LOCKS_WARN_ON(ctx->acquired);
206 if (!IS_ENABLED(CONFIG_PROVE_LOCKING))
207 /*
208 * lockdep will normally handle this,
209 * but fail without anyway
210 */
211 ctx->done_acquire = 1;
212
213 if (!IS_ENABLED(CONFIG_DEBUG_LOCK_ALLOC))
214 /* ensure ww_acquire_fini will still fail if called twice */
215 ctx->acquired = ~0U;
216#endif
217}
218
219/**
220 * ww_mutex_lock - acquire the w/w mutex
221 * @lock: the mutex to be acquired
222 * @ctx: w/w acquire context, or NULL to acquire only a single lock.
223 *
224 * Lock the w/w mutex exclusively for this task.
225 *
226 * Deadlocks within a given w/w class of locks are detected and handled with the
227 * wait/die algorithm. If the lock isn't immediately available this function
228 * will either sleep until it is (wait case). Or it selects the current context
229 * for backing off by returning -EDEADLK (die case). Trying to acquire the
230 * same lock with the same context twice is also detected and signalled by
231 * returning -EALREADY. Returns 0 if the mutex was successfully acquired.
232 *
233 * In the die case the caller must release all currently held w/w mutexes for
234 * the given context and then wait for this contending lock to be available by
235 * calling ww_mutex_lock_slow. Alternatively callers can opt to not acquire this
236 * lock and proceed with trying to acquire further w/w mutexes (e.g. when
237 * scanning through lru lists trying to free resources).
238 *
239 * The mutex must later on be released by the same task that
240 * acquired it. The task may not exit without first unlocking the mutex. Also,
241 * kernel memory where the mutex resides must not be freed with the mutex still
242 * locked. The mutex must first be initialized (or statically defined) before it
243 * can be locked. memset()-ing the mutex to 0 is not allowed. The mutex must be
244 * of the same w/w lock class as was used to initialize the acquire context.
245 *
246 * A mutex acquired with this function must be released with ww_mutex_unlock.
247 */
248extern int /* __must_check */ ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx);
249
250/**
251 * ww_mutex_lock_interruptible - acquire the w/w mutex, interruptible
252 * @lock: the mutex to be acquired
253 * @ctx: w/w acquire context
254 *
255 * Lock the w/w mutex exclusively for this task.
256 *
257 * Deadlocks within a given w/w class of locks are detected and handled with the
258 * wait/die algorithm. If the lock isn't immediately available this function
259 * will either sleep until it is (wait case). Or it selects the current context
260 * for backing off by returning -EDEADLK (die case). Trying to acquire the
261 * same lock with the same context twice is also detected and signalled by
262 * returning -EALREADY. Returns 0 if the mutex was successfully acquired. If a
263 * signal arrives while waiting for the lock then this function returns -EINTR.
264 *
265 * In the die case the caller must release all currently held w/w mutexes for
266 * the given context and then wait for this contending lock to be available by
267 * calling ww_mutex_lock_slow_interruptible. Alternatively callers can opt to
268 * not acquire this lock and proceed with trying to acquire further w/w mutexes
269 * (e.g. when scanning through lru lists trying to free resources).
270 *
271 * The mutex must later on be released by the same task that
272 * acquired it. The task may not exit without first unlocking the mutex. Also,
273 * kernel memory where the mutex resides must not be freed with the mutex still
274 * locked. The mutex must first be initialized (or statically defined) before it
275 * can be locked. memset()-ing the mutex to 0 is not allowed. The mutex must be
276 * of the same w/w lock class as was used to initialize the acquire context.
277 *
278 * A mutex acquired with this function must be released with ww_mutex_unlock.
279 */
280extern int __must_check ww_mutex_lock_interruptible(struct ww_mutex *lock,
281 struct ww_acquire_ctx *ctx);
282
283/**
284 * ww_mutex_lock_slow - slowpath acquiring of the w/w mutex
285 * @lock: the mutex to be acquired
286 * @ctx: w/w acquire context
287 *
288 * Acquires a w/w mutex with the given context after a die case. This function
289 * will sleep until the lock becomes available.
290 *
291 * The caller must have released all w/w mutexes already acquired with the
292 * context and then call this function on the contended lock.
293 *
294 * Afterwards the caller may continue to (re)acquire the other w/w mutexes it
295 * needs with ww_mutex_lock. Note that the -EALREADY return code from
296 * ww_mutex_lock can be used to avoid locking this contended mutex twice.
297 *
298 * It is forbidden to call this function with any other w/w mutexes associated
299 * with the context held. It is forbidden to call this on anything else than the
300 * contending mutex.
301 *
302 * Note that the slowpath lock acquiring can also be done by calling
303 * ww_mutex_lock directly. This function here is simply to help w/w mutex
304 * locking code readability by clearly denoting the slowpath.
305 */
306static inline void
307ww_mutex_lock_slow(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
308{
309 int ret;
310#ifdef DEBUG_WW_MUTEXES
311 DEBUG_LOCKS_WARN_ON(!ctx->contending_lock);
312#endif
313 ret = ww_mutex_lock(lock, ctx);
314 (void)ret;
315}
316
317/**
318 * ww_mutex_lock_slow_interruptible - slowpath acquiring of the w/w mutex, interruptible
319 * @lock: the mutex to be acquired
320 * @ctx: w/w acquire context
321 *
322 * Acquires a w/w mutex with the given context after a die case. This function
323 * will sleep until the lock becomes available and returns 0 when the lock has
324 * been acquired. If a signal arrives while waiting for the lock then this
325 * function returns -EINTR.
326 *
327 * The caller must have released all w/w mutexes already acquired with the
328 * context and then call this function on the contended lock.
329 *
330 * Afterwards the caller may continue to (re)acquire the other w/w mutexes it
331 * needs with ww_mutex_lock. Note that the -EALREADY return code from
332 * ww_mutex_lock can be used to avoid locking this contended mutex twice.
333 *
334 * It is forbidden to call this function with any other w/w mutexes associated
335 * with the given context held. It is forbidden to call this on anything else
336 * than the contending mutex.
337 *
338 * Note that the slowpath lock acquiring can also be done by calling
339 * ww_mutex_lock_interruptible directly. This function here is simply to help
340 * w/w mutex locking code readability by clearly denoting the slowpath.
341 */
342static inline int __must_check
343ww_mutex_lock_slow_interruptible(struct ww_mutex *lock,
344 struct ww_acquire_ctx *ctx)
345{
346#ifdef DEBUG_WW_MUTEXES
347 DEBUG_LOCKS_WARN_ON(!ctx->contending_lock);
348#endif
349 return ww_mutex_lock_interruptible(lock, ctx);
350}
351
352extern void ww_mutex_unlock(struct ww_mutex *lock);
353
354extern int __must_check ww_mutex_trylock(struct ww_mutex *lock,
355 struct ww_acquire_ctx *ctx);
356
357/***
358 * ww_mutex_destroy - mark a w/w mutex unusable
359 * @lock: the mutex to be destroyed
360 *
361 * This function marks the mutex uninitialized, and any subsequent
362 * use of the mutex is forbidden. The mutex must not be locked when
363 * this function is called.
364 */
365static inline void ww_mutex_destroy(struct ww_mutex *lock)
366{
367#ifndef CONFIG_PREEMPT_RT
368 mutex_destroy(lock: &lock->base);
369#endif
370}
371
372/**
373 * ww_mutex_is_locked - is the w/w mutex locked
374 * @lock: the mutex to be queried
375 *
376 * Returns 1 if the mutex is locked, 0 if unlocked.
377 */
378static inline bool ww_mutex_is_locked(struct ww_mutex *lock)
379{
380 return ww_mutex_base_is_locked(&lock->base);
381}
382
383#endif
384