ww_mutex.h

  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(&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->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