Line data Source code
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)
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 :
92 : static void __drm_stack_depot_print(depot_stack_handle_t stack_depot)
93 : {
94 : struct drm_printer p = drm_debug_printer("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 :
111 : static void __drm_stack_depot_init(void)
112 : {
113 : stack_depot_init();
114 : }
115 : #else /* CONFIG_DRM_DEBUG_MODESET_LOCK */
116 : static depot_stack_handle_t __drm_stack_depot_save(void)
117 : {
118 : return 0;
119 : }
120 : static void __drm_stack_depot_print(depot_stack_handle_t stack_depot)
121 : {
122 : }
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 : */
143 0 : void drm_modeset_lock_all(struct drm_device *dev)
144 : {
145 0 : struct drm_mode_config *config = &dev->mode_config;
146 : struct drm_modeset_acquire_ctx *ctx;
147 : int ret;
148 :
149 0 : ctx = kzalloc(sizeof(*ctx), GFP_KERNEL | __GFP_NOFAIL);
150 0 : if (WARN_ON(!ctx))
151 : return;
152 :
153 0 : mutex_lock(&config->mutex);
154 :
155 0 : drm_modeset_acquire_init(ctx, 0);
156 :
157 : retry:
158 0 : ret = drm_modeset_lock_all_ctx(dev, ctx);
159 0 : if (ret < 0) {
160 0 : if (ret == -EDEADLK) {
161 0 : drm_modeset_backoff(ctx);
162 0 : goto retry;
163 : }
164 :
165 0 : drm_modeset_acquire_fini(ctx);
166 0 : kfree(ctx);
167 0 : return;
168 : }
169 0 : ww_acquire_done(&ctx->ww_ctx);
170 :
171 0 : 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 0 : config->acquire_ctx = ctx;
178 :
179 0 : 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 : */
197 0 : void drm_modeset_unlock_all(struct drm_device *dev)
198 : {
199 0 : struct drm_mode_config *config = &dev->mode_config;
200 0 : struct drm_modeset_acquire_ctx *ctx = config->acquire_ctx;
201 :
202 0 : if (WARN_ON(!ctx))
203 : return;
204 :
205 0 : config->acquire_ctx = NULL;
206 0 : drm_modeset_drop_locks(ctx);
207 0 : drm_modeset_acquire_fini(ctx);
208 :
209 0 : kfree(ctx);
210 :
211 0 : 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 : */
221 0 : 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 0 : if (oops_in_progress)
227 : return;
228 :
229 0 : drm_for_each_crtc(crtc, dev)
230 0 : WARN_ON(!drm_modeset_is_locked(&crtc->mutex));
231 :
232 0 : WARN_ON(!drm_modeset_is_locked(&dev->mode_config.connection_mutex));
233 0 : 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 : */
246 5 : void drm_modeset_acquire_init(struct drm_modeset_acquire_ctx *ctx,
247 : uint32_t flags)
248 : {
249 5 : memset(ctx, 0, sizeof(*ctx));
250 10 : ww_acquire_init(&ctx->ww_ctx, &crtc_ww_class);
251 10 : INIT_LIST_HEAD(&ctx->locked);
252 :
253 5 : if (flags & DRM_MODESET_ACQUIRE_INTERRUPTIBLE)
254 0 : ctx->interruptible = true;
255 5 : }
256 : EXPORT_SYMBOL(drm_modeset_acquire_init);
257 :
258 : /**
259 : * drm_modeset_acquire_fini - cleanup acquire context
260 : * @ctx: the acquire context
261 : */
262 5 : void drm_modeset_acquire_fini(struct drm_modeset_acquire_ctx *ctx)
263 : {
264 5 : ww_acquire_fini(&ctx->ww_ctx);
265 5 : }
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 : */
274 5 : void drm_modeset_drop_locks(struct drm_modeset_acquire_ctx *ctx)
275 : {
276 5 : if (WARN_ON(ctx->contended))
277 : __drm_stack_depot_print(ctx->stack_depot);
278 :
279 20 : while (!list_empty(&ctx->locked)) {
280 : struct drm_modeset_lock *lock;
281 :
282 5 : lock = list_first_entry(&ctx->locked,
283 : struct drm_modeset_lock, head);
284 :
285 : drm_modeset_unlock(lock);
286 : }
287 5 : }
288 : EXPORT_SYMBOL(drm_modeset_drop_locks);
289 :
290 10 : 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 10 : if (WARN_ON(ctx->contended))
297 : __drm_stack_depot_print(ctx->stack_depot);
298 :
299 10 : if (ctx->trylock_only) {
300 : lockdep_assert_held(&ctx->ww_ctx);
301 :
302 0 : if (!ww_mutex_trylock(&lock->mutex, NULL))
303 : return -EBUSY;
304 : else
305 0 : return 0;
306 10 : } else if (interruptible && slow) {
307 0 : ret = ww_mutex_lock_slow_interruptible(&lock->mutex, &ctx->ww_ctx);
308 10 : } else if (interruptible) {
309 0 : ret = ww_mutex_lock_interruptible(&lock->mutex, &ctx->ww_ctx);
310 10 : } else if (slow) {
311 0 : ww_mutex_lock_slow(&lock->mutex, &ctx->ww_ctx);
312 0 : ret = 0;
313 : } else {
314 10 : ret = ww_mutex_lock(&lock->mutex, &ctx->ww_ctx);
315 : }
316 10 : if (!ret) {
317 10 : WARN_ON(!list_empty(&lock->head));
318 5 : list_add(&lock->head, &ctx->locked);
319 5 : } 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 0 : } else if (ret == -EDEADLK) {
327 0 : ctx->contended = lock;
328 0 : 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 : */
346 0 : int drm_modeset_backoff(struct drm_modeset_acquire_ctx *ctx)
347 : {
348 0 : struct drm_modeset_lock *contended = ctx->contended;
349 :
350 0 : ctx->contended = NULL;
351 0 : ctx->stack_depot = 0;
352 :
353 0 : if (WARN_ON(!contended))
354 : return 0;
355 :
356 0 : drm_modeset_drop_locks(ctx);
357 :
358 0 : 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 : */
366 17 : void drm_modeset_lock_init(struct drm_modeset_lock *lock)
367 : {
368 34 : ww_mutex_init(&lock->mutex, &crtc_ww_class);
369 34 : INIT_LIST_HEAD(&lock->head);
370 : __drm_stack_depot_init();
371 17 : }
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 : */
392 10 : int drm_modeset_lock(struct drm_modeset_lock *lock,
393 : struct drm_modeset_acquire_ctx *ctx)
394 : {
395 10 : if (ctx)
396 10 : return modeset_lock(lock, ctx, ctx->interruptible, false);
397 :
398 0 : ww_mutex_lock(&lock->mutex, NULL);
399 0 : 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 : */
412 0 : int drm_modeset_lock_single_interruptible(struct drm_modeset_lock *lock)
413 : {
414 0 : 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 : */
422 0 : void drm_modeset_unlock(struct drm_modeset_lock *lock)
423 : {
424 10 : list_del_init(&lock->head);
425 5 : ww_mutex_unlock(&lock->mutex);
426 0 : }
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 : */
449 0 : 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 0 : ret = drm_modeset_lock(&dev->mode_config.connection_mutex, ctx);
458 0 : if (ret)
459 : return ret;
460 :
461 0 : drm_for_each_crtc(crtc, dev) {
462 0 : ret = drm_modeset_lock(&crtc->mutex, ctx);
463 0 : if (ret)
464 : return ret;
465 : }
466 :
467 0 : drm_for_each_plane(plane, dev) {
468 0 : ret = drm_modeset_lock(&plane->mutex, ctx);
469 0 : if (ret)
470 : return ret;
471 : }
472 :
473 0 : drm_for_each_privobj(privobj, dev) {
474 0 : ret = drm_modeset_lock(&privobj->lock, ctx);
475 0 : if (ret)
476 : return ret;
477 : }
478 :
479 : return 0;
480 : }
481 : EXPORT_SYMBOL(drm_modeset_lock_all_ctx);
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