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