xref: /linux/drivers/gpu/drm/drm_modeset_lock.c (revision e154c4fc)
1 /*
2  * Copyright (C) 2014 Red Hat
3  * Author: Rob Clark <robdclark@gmail.com>
4  *
5  * Permission is hereby granted, free of charge, to any person obtaining a
6  * copy of this software and associated documentation files (the "Software"),
7  * to deal in the Software without restriction, including without limitation
8  * the rights to use, copy, modify, merge, publish, distribute, sublicense,
9  * and/or sell copies of the Software, and to permit persons to whom the
10  * Software is furnished to do so, subject to the following conditions:
11  *
12  * The above copyright notice and this permission notice shall be included in
13  * all copies or substantial portions of the Software.
14  *
15  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
16  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
17  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
18  * THE COPYRIGHT HOLDER(S) OR AUTHOR(S) BE LIABLE FOR ANY CLAIM, DAMAGES OR
19  * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
20  * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
21  * OTHER DEALINGS IN THE SOFTWARE.
22  */
23 
24 #include <drm/drm_atomic.h>
25 #include <drm/drm_crtc.h>
26 #include <drm/drm_device.h>
27 #include <drm/drm_modeset_lock.h>
28 #include <drm/drm_print.h>
29 
30 /**
31  * DOC: kms locking
32  *
33  * As KMS moves toward more fine grained locking, and atomic ioctl where
34  * userspace can indirectly control locking order, it becomes necessary
35  * to use &ww_mutex and acquire-contexts to avoid deadlocks.  But because
36  * the locking is more distributed around the driver code, we want a bit
37  * of extra utility/tracking out of our acquire-ctx.  This is provided
38  * by &struct drm_modeset_lock and &struct drm_modeset_acquire_ctx.
39  *
40  * For basic principles of &ww_mutex, see: Documentation/locking/ww-mutex-design.rst
41  *
42  * The basic usage pattern is to::
43  *
44  *     drm_modeset_acquire_init(ctx, DRM_MODESET_ACQUIRE_INTERRUPTIBLE)
45  *     retry:
46  *     foreach (lock in random_ordered_set_of_locks) {
47  *         ret = drm_modeset_lock(lock, ctx)
48  *         if (ret == -EDEADLK) {
49  *             ret = drm_modeset_backoff(ctx);
50  *             if (!ret)
51  *                 goto retry;
52  *         }
53  *         if (ret)
54  *             goto out;
55  *     }
56  *     ... do stuff ...
57  *     out:
58  *     drm_modeset_drop_locks(ctx);
59  *     drm_modeset_acquire_fini(ctx);
60  *
61  * For convenience this control flow is implemented in
62  * DRM_MODESET_LOCK_ALL_BEGIN() and DRM_MODESET_LOCK_ALL_END() for the case
63  * where all modeset locks need to be taken through drm_modeset_lock_all_ctx().
64  *
65  * If all that is needed is a single modeset lock, then the &struct
66  * drm_modeset_acquire_ctx is not needed and the locking can be simplified
67  * by passing a NULL instead of ctx in the drm_modeset_lock() call or
68  * calling  drm_modeset_lock_single_interruptible(). To unlock afterwards
69  * call drm_modeset_unlock().
70  *
71  * On top of these per-object locks using &ww_mutex there's also an overall
72  * &drm_mode_config.mutex, for protecting everything else. Mostly this means
73  * probe state of connectors, and preventing hotplug add/removal of connectors.
74  *
75  * Finally there's a bunch of dedicated locks to protect drm core internal
76  * lists and lookup data structures.
77  */
78 
79 static DEFINE_WW_CLASS(crtc_ww_class);
80 
81 #if IS_ENABLED(CONFIG_DRM_DEBUG_MODESET_LOCK)
__drm_stack_depot_save(void)82 static noinline depot_stack_handle_t __drm_stack_depot_save(void)
83 {
84 	unsigned long entries[8];
85 	unsigned int n;
86 
87 	n = stack_trace_save(entries, ARRAY_SIZE(entries), 1);
88 
89 	return stack_depot_save(entries, n, GFP_NOWAIT | __GFP_NOWARN);
90 }
91 
__drm_stack_depot_print(depot_stack_handle_t stack_depot)92 static void __drm_stack_depot_print(depot_stack_handle_t stack_depot)
93 {
94 	struct drm_printer p = drm_dbg_printer(NULL, DRM_UT_KMS, "drm_modeset_lock");
95 	unsigned long *entries;
96 	unsigned int nr_entries;
97 	char *buf;
98 
99 	buf = kmalloc(PAGE_SIZE, GFP_NOWAIT | __GFP_NOWARN);
100 	if (!buf)
101 		return;
102 
103 	nr_entries = stack_depot_fetch(stack_depot, &entries);
104 	stack_trace_snprint(buf, PAGE_SIZE, entries, nr_entries, 2);
105 
106 	drm_printf(&p, "attempting to lock a contended lock without backoff:\n%s", buf);
107 
108 	kfree(buf);
109 }
110 
__drm_stack_depot_init(void)111 static void __drm_stack_depot_init(void)
112 {
113 	stack_depot_init();
114 }
115 #else /* CONFIG_DRM_DEBUG_MODESET_LOCK */
__drm_stack_depot_save(void)116 static depot_stack_handle_t __drm_stack_depot_save(void)
117 {
118 	return 0;
119 }
__drm_stack_depot_print(depot_stack_handle_t stack_depot)120 static void __drm_stack_depot_print(depot_stack_handle_t stack_depot)
121 {
122 }
__drm_stack_depot_init(void)123 static void __drm_stack_depot_init(void)
124 {
125 }
126 #endif /* CONFIG_DRM_DEBUG_MODESET_LOCK */
127 
128 /**
129  * drm_modeset_lock_all - take all modeset locks
130  * @dev: DRM device
131  *
132  * This function takes all modeset locks, suitable where a more fine-grained
133  * scheme isn't (yet) implemented. Locks must be dropped by calling the
134  * drm_modeset_unlock_all() function.
135  *
136  * This function is deprecated. It allocates a lock acquisition context and
137  * stores it in &drm_device.mode_config. This facilitate conversion of
138  * existing code because it removes the need to manually deal with the
139  * acquisition context, but it is also brittle because the context is global
140  * and care must be taken not to nest calls. New code should use the
141  * drm_modeset_lock_all_ctx() function and pass in the context explicitly.
142  */
drm_modeset_lock_all(struct drm_device * dev)143 void drm_modeset_lock_all(struct drm_device *dev)
144 {
145 	struct drm_mode_config *config = &dev->mode_config;
146 	struct drm_modeset_acquire_ctx *ctx;
147 	int ret;
148 
149 	ctx = kzalloc(sizeof(*ctx), GFP_KERNEL | __GFP_NOFAIL);
150 	if (WARN_ON(!ctx))
151 		return;
152 
153 	mutex_lock(&config->mutex);
154 
155 	drm_modeset_acquire_init(ctx, 0);
156 
157 retry:
158 	ret = drm_modeset_lock_all_ctx(dev, ctx);
159 	if (ret < 0) {
160 		if (ret == -EDEADLK) {
161 			drm_modeset_backoff(ctx);
162 			goto retry;
163 		}
164 
165 		drm_modeset_acquire_fini(ctx);
166 		kfree(ctx);
167 		return;
168 	}
169 	ww_acquire_done(&ctx->ww_ctx);
170 
171 	WARN_ON(config->acquire_ctx);
172 
173 	/*
174 	 * We hold the locks now, so it is safe to stash the acquisition
175 	 * context for drm_modeset_unlock_all().
176 	 */
177 	config->acquire_ctx = ctx;
178 
179 	drm_warn_on_modeset_not_all_locked(dev);
180 }
181 EXPORT_SYMBOL(drm_modeset_lock_all);
182 
183 /**
184  * drm_modeset_unlock_all - drop all modeset locks
185  * @dev: DRM device
186  *
187  * This function drops all modeset locks taken by a previous call to the
188  * drm_modeset_lock_all() function.
189  *
190  * This function is deprecated. It uses the lock acquisition context stored
191  * in &drm_device.mode_config. This facilitates conversion of existing
192  * code because it removes the need to manually deal with the acquisition
193  * context, but it is also brittle because the context is global and care must
194  * be taken not to nest calls. New code should pass the acquisition context
195  * directly to the drm_modeset_drop_locks() function.
196  */
drm_modeset_unlock_all(struct drm_device * dev)197 void drm_modeset_unlock_all(struct drm_device *dev)
198 {
199 	struct drm_mode_config *config = &dev->mode_config;
200 	struct drm_modeset_acquire_ctx *ctx = config->acquire_ctx;
201 
202 	if (WARN_ON(!ctx))
203 		return;
204 
205 	config->acquire_ctx = NULL;
206 	drm_modeset_drop_locks(ctx);
207 	drm_modeset_acquire_fini(ctx);
208 
209 	kfree(ctx);
210 
211 	mutex_unlock(&dev->mode_config.mutex);
212 }
213 EXPORT_SYMBOL(drm_modeset_unlock_all);
214 
215 /**
216  * drm_warn_on_modeset_not_all_locked - check that all modeset locks are locked
217  * @dev: device
218  *
219  * Useful as a debug assert.
220  */
drm_warn_on_modeset_not_all_locked(struct drm_device * dev)221 void drm_warn_on_modeset_not_all_locked(struct drm_device *dev)
222 {
223 	struct drm_crtc *crtc;
224 
225 	/* Locking is currently fubar in the panic handler. */
226 	if (oops_in_progress)
227 		return;
228 
229 	drm_for_each_crtc(crtc, dev)
230 		WARN_ON(!drm_modeset_is_locked(&crtc->mutex));
231 
232 	WARN_ON(!drm_modeset_is_locked(&dev->mode_config.connection_mutex));
233 	WARN_ON(!mutex_is_locked(&dev->mode_config.mutex));
234 }
235 EXPORT_SYMBOL(drm_warn_on_modeset_not_all_locked);
236 
237 /**
238  * drm_modeset_acquire_init - initialize acquire context
239  * @ctx: the acquire context
240  * @flags: 0 or %DRM_MODESET_ACQUIRE_INTERRUPTIBLE
241  *
242  * When passing %DRM_MODESET_ACQUIRE_INTERRUPTIBLE to @flags,
243  * all calls to drm_modeset_lock() will perform an interruptible
244  * wait.
245  */
drm_modeset_acquire_init(struct drm_modeset_acquire_ctx * ctx,uint32_t flags)246 void drm_modeset_acquire_init(struct drm_modeset_acquire_ctx *ctx,
247 		uint32_t flags)
248 {
249 	memset(ctx, 0, sizeof(*ctx));
250 	ww_acquire_init(&ctx->ww_ctx, &crtc_ww_class);
251 	INIT_LIST_HEAD(&ctx->locked);
252 
253 	if (flags & DRM_MODESET_ACQUIRE_INTERRUPTIBLE)
254 		ctx->interruptible = true;
255 }
256 EXPORT_SYMBOL(drm_modeset_acquire_init);
257 
258 /**
259  * drm_modeset_acquire_fini - cleanup acquire context
260  * @ctx: the acquire context
261  */
drm_modeset_acquire_fini(struct drm_modeset_acquire_ctx * ctx)262 void drm_modeset_acquire_fini(struct drm_modeset_acquire_ctx *ctx)
263 {
264 	ww_acquire_fini(&ctx->ww_ctx);
265 }
266 EXPORT_SYMBOL(drm_modeset_acquire_fini);
267 
268 /**
269  * drm_modeset_drop_locks - drop all locks
270  * @ctx: the acquire context
271  *
272  * Drop all locks currently held against this acquire context.
273  */
drm_modeset_drop_locks(struct drm_modeset_acquire_ctx * ctx)274 void drm_modeset_drop_locks(struct drm_modeset_acquire_ctx *ctx)
275 {
276 	if (WARN_ON(ctx->contended))
277 		__drm_stack_depot_print(ctx->stack_depot);
278 
279 	while (!list_empty(&ctx->locked)) {
280 		struct drm_modeset_lock *lock;
281 
282 		lock = list_first_entry(&ctx->locked,
283 				struct drm_modeset_lock, head);
284 
285 		drm_modeset_unlock(lock);
286 	}
287 }
288 EXPORT_SYMBOL(drm_modeset_drop_locks);
289 
modeset_lock(struct drm_modeset_lock * lock,struct drm_modeset_acquire_ctx * ctx,bool interruptible,bool slow)290 static inline int modeset_lock(struct drm_modeset_lock *lock,
291 		struct drm_modeset_acquire_ctx *ctx,
292 		bool interruptible, bool slow)
293 {
294 	int ret;
295 
296 	if (WARN_ON(ctx->contended))
297 		__drm_stack_depot_print(ctx->stack_depot);
298 
299 	if (ctx->trylock_only) {
300 		lockdep_assert_held(&ctx->ww_ctx);
301 
302 		if (!ww_mutex_trylock(&lock->mutex, NULL))
303 			return -EBUSY;
304 		else
305 			return 0;
306 	} else if (interruptible && slow) {
307 		ret = ww_mutex_lock_slow_interruptible(&lock->mutex, &ctx->ww_ctx);
308 	} else if (interruptible) {
309 		ret = ww_mutex_lock_interruptible(&lock->mutex, &ctx->ww_ctx);
310 	} else if (slow) {
311 		ww_mutex_lock_slow(&lock->mutex, &ctx->ww_ctx);
312 		ret = 0;
313 	} else {
314 		ret = ww_mutex_lock(&lock->mutex, &ctx->ww_ctx);
315 	}
316 	if (!ret) {
317 		WARN_ON(!list_empty(&lock->head));
318 		list_add(&lock->head, &ctx->locked);
319 	} else if (ret == -EALREADY) {
320 		/* we already hold the lock.. this is fine.  For atomic
321 		 * we will need to be able to drm_modeset_lock() things
322 		 * without having to keep track of what is already locked
323 		 * or not.
324 		 */
325 		ret = 0;
326 	} else if (ret == -EDEADLK) {
327 		ctx->contended = lock;
328 		ctx->stack_depot = __drm_stack_depot_save();
329 	}
330 
331 	return ret;
332 }
333 
334 /**
335  * drm_modeset_backoff - deadlock avoidance backoff
336  * @ctx: the acquire context
337  *
338  * If deadlock is detected (ie. drm_modeset_lock() returns -EDEADLK),
339  * you must call this function to drop all currently held locks and
340  * block until the contended lock becomes available.
341  *
342  * This function returns 0 on success, or -ERESTARTSYS if this context
343  * is initialized with %DRM_MODESET_ACQUIRE_INTERRUPTIBLE and the
344  * wait has been interrupted.
345  */
drm_modeset_backoff(struct drm_modeset_acquire_ctx * ctx)346 int drm_modeset_backoff(struct drm_modeset_acquire_ctx *ctx)
347 {
348 	struct drm_modeset_lock *contended = ctx->contended;
349 
350 	ctx->contended = NULL;
351 	ctx->stack_depot = 0;
352 
353 	if (WARN_ON(!contended))
354 		return 0;
355 
356 	drm_modeset_drop_locks(ctx);
357 
358 	return modeset_lock(contended, ctx, ctx->interruptible, true);
359 }
360 EXPORT_SYMBOL(drm_modeset_backoff);
361 
362 /**
363  * drm_modeset_lock_init - initialize lock
364  * @lock: lock to init
365  */
drm_modeset_lock_init(struct drm_modeset_lock * lock)366 void drm_modeset_lock_init(struct drm_modeset_lock *lock)
367 {
368 	ww_mutex_init(&lock->mutex, &crtc_ww_class);
369 	INIT_LIST_HEAD(&lock->head);
370 	__drm_stack_depot_init();
371 }
372 EXPORT_SYMBOL(drm_modeset_lock_init);
373 
374 /**
375  * drm_modeset_lock - take modeset lock
376  * @lock: lock to take
377  * @ctx: acquire ctx
378  *
379  * If @ctx is not NULL, then its ww acquire context is used and the
380  * lock will be tracked by the context and can be released by calling
381  * drm_modeset_drop_locks().  If -EDEADLK is returned, this means a
382  * deadlock scenario has been detected and it is an error to attempt
383  * to take any more locks without first calling drm_modeset_backoff().
384  *
385  * If the @ctx is not NULL and initialized with
386  * %DRM_MODESET_ACQUIRE_INTERRUPTIBLE, this function will fail with
387  * -ERESTARTSYS when interrupted.
388  *
389  * If @ctx is NULL then the function call behaves like a normal,
390  * uninterruptible non-nesting mutex_lock() call.
391  */
drm_modeset_lock(struct drm_modeset_lock * lock,struct drm_modeset_acquire_ctx * ctx)392 int drm_modeset_lock(struct drm_modeset_lock *lock,
393 		struct drm_modeset_acquire_ctx *ctx)
394 {
395 	if (ctx)
396 		return modeset_lock(lock, ctx, ctx->interruptible, false);
397 
398 	ww_mutex_lock(&lock->mutex, NULL);
399 	return 0;
400 }
401 EXPORT_SYMBOL(drm_modeset_lock);
402 
403 /**
404  * drm_modeset_lock_single_interruptible - take a single modeset lock
405  * @lock: lock to take
406  *
407  * This function behaves as drm_modeset_lock() with a NULL context,
408  * but performs interruptible waits.
409  *
410  * This function returns 0 on success, or -ERESTARTSYS when interrupted.
411  */
drm_modeset_lock_single_interruptible(struct drm_modeset_lock * lock)412 int drm_modeset_lock_single_interruptible(struct drm_modeset_lock *lock)
413 {
414 	return ww_mutex_lock_interruptible(&lock->mutex, NULL);
415 }
416 EXPORT_SYMBOL(drm_modeset_lock_single_interruptible);
417 
418 /**
419  * drm_modeset_unlock - drop modeset lock
420  * @lock: lock to release
421  */
drm_modeset_unlock(struct drm_modeset_lock * lock)422 void drm_modeset_unlock(struct drm_modeset_lock *lock)
423 {
424 	list_del_init(&lock->head);
425 	ww_mutex_unlock(&lock->mutex);
426 }
427 EXPORT_SYMBOL(drm_modeset_unlock);
428 
429 /**
430  * drm_modeset_lock_all_ctx - take all modeset locks
431  * @dev: DRM device
432  * @ctx: lock acquisition context
433  *
434  * This function takes all modeset locks, suitable where a more fine-grained
435  * scheme isn't (yet) implemented.
436  *
437  * Unlike drm_modeset_lock_all(), it doesn't take the &drm_mode_config.mutex
438  * since that lock isn't required for modeset state changes. Callers which
439  * need to grab that lock too need to do so outside of the acquire context
440  * @ctx.
441  *
442  * Locks acquired with this function should be released by calling the
443  * drm_modeset_drop_locks() function on @ctx.
444  *
445  * See also: DRM_MODESET_LOCK_ALL_BEGIN() and DRM_MODESET_LOCK_ALL_END()
446  *
447  * Returns: 0 on success or a negative error-code on failure.
448  */
drm_modeset_lock_all_ctx(struct drm_device * dev,struct drm_modeset_acquire_ctx * ctx)449 int drm_modeset_lock_all_ctx(struct drm_device *dev,
450 			     struct drm_modeset_acquire_ctx *ctx)
451 {
452 	struct drm_private_obj *privobj;
453 	struct drm_crtc *crtc;
454 	struct drm_plane *plane;
455 	int ret;
456 
457 	ret = drm_modeset_lock(&dev->mode_config.connection_mutex, ctx);
458 	if (ret)
459 		return ret;
460 
461 	drm_for_each_crtc(crtc, dev) {
462 		ret = drm_modeset_lock(&crtc->mutex, ctx);
463 		if (ret)
464 			return ret;
465 	}
466 
467 	drm_for_each_plane(plane, dev) {
468 		ret = drm_modeset_lock(&plane->mutex, ctx);
469 		if (ret)
470 			return ret;
471 	}
472 
473 	drm_for_each_privobj(privobj, dev) {
474 		ret = drm_modeset_lock(&privobj->lock, ctx);
475 		if (ret)
476 			return ret;
477 	}
478 
479 	return 0;
480 }
481 EXPORT_SYMBOL(drm_modeset_lock_all_ctx);
482