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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
79static DEFINE_WW_CLASS(crtc_ww_class);
80
81#if IS_ENABLED(CONFIG_DRM_DEBUG_MODESET_LOCK)
82static 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
92static 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
111static void __drm_stack_depot_init(void)
112{
113 stack_depot_init();
114}
115#else /* CONFIG_DRM_DEBUG_MODESET_LOCK */
116static depot_stack_handle_t __drm_stack_depot_save(void)
117{
118 return 0;
119}
120static void __drm_stack_depot_print(depot_stack_handle_t stack_depot)
121{
122}
123static 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 */
143void 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
157retry:
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}
181EXPORT_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 */
197void 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}
213EXPORT_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 */
221void 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}
235EXPORT_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 */
246void 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}
256EXPORT_SYMBOL(drm_modeset_acquire_init);
257
258/**
259 * drm_modeset_acquire_fini - cleanup acquire context
260 * @ctx: the acquire context
261 */
262void drm_modeset_acquire_fini(struct drm_modeset_acquire_ctx *ctx)
263{
264 ww_acquire_fini(&ctx->ww_ctx);
265}
266EXPORT_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 */
274void 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}
288EXPORT_SYMBOL(drm_modeset_drop_locks);
289
290static 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 */
346int 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}
360EXPORT_SYMBOL(drm_modeset_backoff);
361
362/**
363 * drm_modeset_lock_init - initialize lock
364 * @lock: lock to init
365 */
366void 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}
372EXPORT_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 */
392int 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}
401EXPORT_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 */
412int drm_modeset_lock_single_interruptible(struct drm_modeset_lock *lock)
413{
414 return ww_mutex_lock_interruptible(&lock->mutex, NULL);
415}
416EXPORT_SYMBOL(drm_modeset_lock_single_interruptible);
417
418/**
419 * drm_modeset_unlock - drop modeset lock
420 * @lock: lock to release
421 */
422void drm_modeset_unlock(struct drm_modeset_lock *lock)
423{
424 list_del_init(&lock->head);
425 ww_mutex_unlock(&lock->mutex);
426}
427EXPORT_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 */
449int 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}
481EXPORT_SYMBOL(drm_modeset_lock_all_ctx);
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/drmP.h>
25#include <drm/drm_crtc.h>
26#include <drm/drm_modeset_lock.h>
27
28/**
29 * DOC: kms locking
30 *
31 * As KMS moves toward more fine grained locking, and atomic ioctl where
32 * userspace can indirectly control locking order, it becomes necessary
33 * to use &ww_mutex and acquire-contexts to avoid deadlocks. But because
34 * the locking is more distributed around the driver code, we want a bit
35 * of extra utility/tracking out of our acquire-ctx. This is provided
36 * by drm_modeset_lock / drm_modeset_acquire_ctx.
37 *
38 * For basic principles of &ww_mutex, see: Documentation/locking/ww-mutex-design.txt
39 *
40 * The basic usage pattern is to::
41 *
42 * drm_modeset_acquire_init(&ctx)
43 * retry:
44 * foreach (lock in random_ordered_set_of_locks) {
45 * ret = drm_modeset_lock(lock, &ctx)
46 * if (ret == -EDEADLK) {
47 * drm_modeset_backoff(&ctx);
48 * goto retry;
49 * }
50 * }
51 * ... do stuff ...
52 * drm_modeset_drop_locks(&ctx);
53 * drm_modeset_acquire_fini(&ctx);
54 *
55 * On top of of these per-object locks using &ww_mutex there's also an overall
56 * dev->mode_config.lock, for protecting everything else. Mostly this means
57 * probe state of connectors, and preventing hotplug add/removal of connectors.
58 *
59 * Finally there's a bunch of dedicated locks to protect drm core internal
60 * lists and lookup data structures.
61 */
62
63static DEFINE_WW_CLASS(crtc_ww_class);
64
65/**
66 * drm_modeset_lock_all - take all modeset locks
67 * @dev: DRM device
68 *
69 * This function takes all modeset locks, suitable where a more fine-grained
70 * scheme isn't (yet) implemented. Locks must be dropped by calling the
71 * drm_modeset_unlock_all() function.
72 *
73 * This function is deprecated. It allocates a lock acquisition context and
74 * stores it in the DRM device's ->mode_config. This facilitate conversion of
75 * existing code because it removes the need to manually deal with the
76 * acquisition context, but it is also brittle because the context is global
77 * and care must be taken not to nest calls. New code should use the
78 * drm_modeset_lock_all_ctx() function and pass in the context explicitly.
79 */
80void drm_modeset_lock_all(struct drm_device *dev)
81{
82 struct drm_mode_config *config = &dev->mode_config;
83 struct drm_modeset_acquire_ctx *ctx;
84 int ret;
85
86 ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
87 if (WARN_ON(!ctx))
88 return;
89
90 mutex_lock(&config->mutex);
91
92 drm_modeset_acquire_init(ctx, 0);
93
94retry:
95 ret = drm_modeset_lock_all_ctx(dev, ctx);
96 if (ret < 0) {
97 if (ret == -EDEADLK) {
98 drm_modeset_backoff(ctx);
99 goto retry;
100 }
101
102 drm_modeset_acquire_fini(ctx);
103 kfree(ctx);
104 return;
105 }
106
107 WARN_ON(config->acquire_ctx);
108
109 /*
110 * We hold the locks now, so it is safe to stash the acquisition
111 * context for drm_modeset_unlock_all().
112 */
113 config->acquire_ctx = ctx;
114
115 drm_warn_on_modeset_not_all_locked(dev);
116}
117EXPORT_SYMBOL(drm_modeset_lock_all);
118
119/**
120 * drm_modeset_unlock_all - drop all modeset locks
121 * @dev: DRM device
122 *
123 * This function drops all modeset locks taken by a previous call to the
124 * drm_modeset_lock_all() function.
125 *
126 * This function is deprecated. It uses the lock acquisition context stored
127 * in the DRM device's ->mode_config. This facilitates conversion of existing
128 * code because it removes the need to manually deal with the acquisition
129 * context, but it is also brittle because the context is global and care must
130 * be taken not to nest calls. New code should pass the acquisition context
131 * directly to the drm_modeset_drop_locks() function.
132 */
133void drm_modeset_unlock_all(struct drm_device *dev)
134{
135 struct drm_mode_config *config = &dev->mode_config;
136 struct drm_modeset_acquire_ctx *ctx = config->acquire_ctx;
137
138 if (WARN_ON(!ctx))
139 return;
140
141 config->acquire_ctx = NULL;
142 drm_modeset_drop_locks(ctx);
143 drm_modeset_acquire_fini(ctx);
144
145 kfree(ctx);
146
147 mutex_unlock(&dev->mode_config.mutex);
148}
149EXPORT_SYMBOL(drm_modeset_unlock_all);
150
151/**
152 * drm_modeset_lock_crtc - lock crtc with hidden acquire ctx for a plane update
153 * @crtc: DRM CRTC
154 * @plane: DRM plane to be updated on @crtc
155 *
156 * This function locks the given crtc and plane (which should be either the
157 * primary or cursor plane) using a hidden acquire context. This is necessary so
158 * that drivers internally using the atomic interfaces can grab further locks
159 * with the lock acquire context.
160 *
161 * Note that @plane can be NULL, e.g. when the cursor support hasn't yet been
162 * converted to universal planes yet.
163 */
164void drm_modeset_lock_crtc(struct drm_crtc *crtc,
165 struct drm_plane *plane)
166{
167 struct drm_modeset_acquire_ctx *ctx;
168 int ret;
169
170 ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
171 if (WARN_ON(!ctx))
172 return;
173
174 drm_modeset_acquire_init(ctx, 0);
175
176retry:
177 ret = drm_modeset_lock(&crtc->mutex, ctx);
178 if (ret)
179 goto fail;
180
181 if (plane) {
182 ret = drm_modeset_lock(&plane->mutex, ctx);
183 if (ret)
184 goto fail;
185
186 if (plane->crtc) {
187 ret = drm_modeset_lock(&plane->crtc->mutex, ctx);
188 if (ret)
189 goto fail;
190 }
191 }
192
193 WARN_ON(crtc->acquire_ctx);
194
195 /* now we hold the locks, so now that it is safe, stash the
196 * ctx for drm_modeset_unlock_crtc():
197 */
198 crtc->acquire_ctx = ctx;
199
200 return;
201
202fail:
203 if (ret == -EDEADLK) {
204 drm_modeset_backoff(ctx);
205 goto retry;
206 }
207}
208EXPORT_SYMBOL(drm_modeset_lock_crtc);
209
210/**
211 * drm_modeset_legacy_acquire_ctx - find acquire ctx for legacy ioctls
212 * @crtc: drm crtc
213 *
214 * Legacy ioctl operations like cursor updates or page flips only have per-crtc
215 * locking, and store the acquire ctx in the corresponding crtc. All other
216 * legacy operations take all locks and use a global acquire context. This
217 * function grabs the right one.
218 */
219struct drm_modeset_acquire_ctx *
220drm_modeset_legacy_acquire_ctx(struct drm_crtc *crtc)
221{
222 if (crtc->acquire_ctx)
223 return crtc->acquire_ctx;
224
225 WARN_ON(!crtc->dev->mode_config.acquire_ctx);
226
227 return crtc->dev->mode_config.acquire_ctx;
228}
229EXPORT_SYMBOL(drm_modeset_legacy_acquire_ctx);
230
231/**
232 * drm_modeset_unlock_crtc - drop crtc lock
233 * @crtc: drm crtc
234 *
235 * This drops the crtc lock acquire with drm_modeset_lock_crtc() and all other
236 * locks acquired through the hidden context.
237 */
238void drm_modeset_unlock_crtc(struct drm_crtc *crtc)
239{
240 struct drm_modeset_acquire_ctx *ctx = crtc->acquire_ctx;
241
242 if (WARN_ON(!ctx))
243 return;
244
245 crtc->acquire_ctx = NULL;
246 drm_modeset_drop_locks(ctx);
247 drm_modeset_acquire_fini(ctx);
248
249 kfree(ctx);
250}
251EXPORT_SYMBOL(drm_modeset_unlock_crtc);
252
253/**
254 * drm_warn_on_modeset_not_all_locked - check that all modeset locks are locked
255 * @dev: device
256 *
257 * Useful as a debug assert.
258 */
259void drm_warn_on_modeset_not_all_locked(struct drm_device *dev)
260{
261 struct drm_crtc *crtc;
262
263 /* Locking is currently fubar in the panic handler. */
264 if (oops_in_progress)
265 return;
266
267 drm_for_each_crtc(crtc, dev)
268 WARN_ON(!drm_modeset_is_locked(&crtc->mutex));
269
270 WARN_ON(!drm_modeset_is_locked(&dev->mode_config.connection_mutex));
271 WARN_ON(!mutex_is_locked(&dev->mode_config.mutex));
272}
273EXPORT_SYMBOL(drm_warn_on_modeset_not_all_locked);
274
275/**
276 * drm_modeset_acquire_init - initialize acquire context
277 * @ctx: the acquire context
278 * @flags: for future
279 */
280void drm_modeset_acquire_init(struct drm_modeset_acquire_ctx *ctx,
281 uint32_t flags)
282{
283 memset(ctx, 0, sizeof(*ctx));
284 ww_acquire_init(&ctx->ww_ctx, &crtc_ww_class);
285 INIT_LIST_HEAD(&ctx->locked);
286}
287EXPORT_SYMBOL(drm_modeset_acquire_init);
288
289/**
290 * drm_modeset_acquire_fini - cleanup acquire context
291 * @ctx: the acquire context
292 */
293void drm_modeset_acquire_fini(struct drm_modeset_acquire_ctx *ctx)
294{
295 ww_acquire_fini(&ctx->ww_ctx);
296}
297EXPORT_SYMBOL(drm_modeset_acquire_fini);
298
299/**
300 * drm_modeset_drop_locks - drop all locks
301 * @ctx: the acquire context
302 *
303 * Drop all locks currently held against this acquire context.
304 */
305void drm_modeset_drop_locks(struct drm_modeset_acquire_ctx *ctx)
306{
307 WARN_ON(ctx->contended);
308 while (!list_empty(&ctx->locked)) {
309 struct drm_modeset_lock *lock;
310
311 lock = list_first_entry(&ctx->locked,
312 struct drm_modeset_lock, head);
313
314 drm_modeset_unlock(lock);
315 }
316}
317EXPORT_SYMBOL(drm_modeset_drop_locks);
318
319static inline int modeset_lock(struct drm_modeset_lock *lock,
320 struct drm_modeset_acquire_ctx *ctx,
321 bool interruptible, bool slow)
322{
323 int ret;
324
325 WARN_ON(ctx->contended);
326
327 if (ctx->trylock_only) {
328 lockdep_assert_held(&ctx->ww_ctx);
329
330 if (!ww_mutex_trylock(&lock->mutex))
331 return -EBUSY;
332 else
333 return 0;
334 } else if (interruptible && slow) {
335 ret = ww_mutex_lock_slow_interruptible(&lock->mutex, &ctx->ww_ctx);
336 } else if (interruptible) {
337 ret = ww_mutex_lock_interruptible(&lock->mutex, &ctx->ww_ctx);
338 } else if (slow) {
339 ww_mutex_lock_slow(&lock->mutex, &ctx->ww_ctx);
340 ret = 0;
341 } else {
342 ret = ww_mutex_lock(&lock->mutex, &ctx->ww_ctx);
343 }
344 if (!ret) {
345 WARN_ON(!list_empty(&lock->head));
346 list_add(&lock->head, &ctx->locked);
347 } else if (ret == -EALREADY) {
348 /* we already hold the lock.. this is fine. For atomic
349 * we will need to be able to drm_modeset_lock() things
350 * without having to keep track of what is already locked
351 * or not.
352 */
353 ret = 0;
354 } else if (ret == -EDEADLK) {
355 ctx->contended = lock;
356 }
357
358 return ret;
359}
360
361static int modeset_backoff(struct drm_modeset_acquire_ctx *ctx,
362 bool interruptible)
363{
364 struct drm_modeset_lock *contended = ctx->contended;
365
366 ctx->contended = NULL;
367
368 if (WARN_ON(!contended))
369 return 0;
370
371 drm_modeset_drop_locks(ctx);
372
373 return modeset_lock(contended, ctx, interruptible, true);
374}
375
376/**
377 * drm_modeset_backoff - deadlock avoidance backoff
378 * @ctx: the acquire context
379 *
380 * If deadlock is detected (ie. drm_modeset_lock() returns -EDEADLK),
381 * you must call this function to drop all currently held locks and
382 * block until the contended lock becomes available.
383 */
384void drm_modeset_backoff(struct drm_modeset_acquire_ctx *ctx)
385{
386 modeset_backoff(ctx, false);
387}
388EXPORT_SYMBOL(drm_modeset_backoff);
389
390/**
391 * drm_modeset_backoff_interruptible - deadlock avoidance backoff
392 * @ctx: the acquire context
393 *
394 * Interruptible version of drm_modeset_backoff()
395 */
396int drm_modeset_backoff_interruptible(struct drm_modeset_acquire_ctx *ctx)
397{
398 return modeset_backoff(ctx, true);
399}
400EXPORT_SYMBOL(drm_modeset_backoff_interruptible);
401
402/**
403 * drm_modeset_lock_init - initialize lock
404 * @lock: lock to init
405 */
406void drm_modeset_lock_init(struct drm_modeset_lock *lock)
407{
408 ww_mutex_init(&lock->mutex, &crtc_ww_class);
409 INIT_LIST_HEAD(&lock->head);
410}
411EXPORT_SYMBOL(drm_modeset_lock_init);
412
413/**
414 * drm_modeset_lock - take modeset lock
415 * @lock: lock to take
416 * @ctx: acquire ctx
417 *
418 * If ctx is not NULL, then its ww acquire context is used and the
419 * lock will be tracked by the context and can be released by calling
420 * drm_modeset_drop_locks(). If -EDEADLK is returned, this means a
421 * deadlock scenario has been detected and it is an error to attempt
422 * to take any more locks without first calling drm_modeset_backoff().
423 */
424int drm_modeset_lock(struct drm_modeset_lock *lock,
425 struct drm_modeset_acquire_ctx *ctx)
426{
427 if (ctx)
428 return modeset_lock(lock, ctx, false, false);
429
430 ww_mutex_lock(&lock->mutex, NULL);
431 return 0;
432}
433EXPORT_SYMBOL(drm_modeset_lock);
434
435/**
436 * drm_modeset_lock_interruptible - take modeset lock
437 * @lock: lock to take
438 * @ctx: acquire ctx
439 *
440 * Interruptible version of drm_modeset_lock()
441 */
442int drm_modeset_lock_interruptible(struct drm_modeset_lock *lock,
443 struct drm_modeset_acquire_ctx *ctx)
444{
445 if (ctx)
446 return modeset_lock(lock, ctx, true, false);
447
448 return ww_mutex_lock_interruptible(&lock->mutex, NULL);
449}
450EXPORT_SYMBOL(drm_modeset_lock_interruptible);
451
452/**
453 * drm_modeset_unlock - drop modeset lock
454 * @lock: lock to release
455 */
456void drm_modeset_unlock(struct drm_modeset_lock *lock)
457{
458 list_del_init(&lock->head);
459 ww_mutex_unlock(&lock->mutex);
460}
461EXPORT_SYMBOL(drm_modeset_unlock);
462
463/**
464 * drm_modeset_lock_all_ctx - take all modeset locks
465 * @dev: DRM device
466 * @ctx: lock acquisition context
467 *
468 * This function takes all modeset locks, suitable where a more fine-grained
469 * scheme isn't (yet) implemented.
470 *
471 * Unlike drm_modeset_lock_all(), it doesn't take the dev->mode_config.mutex
472 * since that lock isn't required for modeset state changes. Callers which
473 * need to grab that lock too need to do so outside of the acquire context
474 * @ctx.
475 *
476 * Locks acquired with this function should be released by calling the
477 * drm_modeset_drop_locks() function on @ctx.
478 *
479 * Returns: 0 on success or a negative error-code on failure.
480 */
481int drm_modeset_lock_all_ctx(struct drm_device *dev,
482 struct drm_modeset_acquire_ctx *ctx)
483{
484 struct drm_crtc *crtc;
485 struct drm_plane *plane;
486 int ret;
487
488 ret = drm_modeset_lock(&dev->mode_config.connection_mutex, ctx);
489 if (ret)
490 return ret;
491
492 drm_for_each_crtc(crtc, dev) {
493 ret = drm_modeset_lock(&crtc->mutex, ctx);
494 if (ret)
495 return ret;
496 }
497
498 drm_for_each_plane(plane, dev) {
499 ret = drm_modeset_lock(&plane->mutex, ctx);
500 if (ret)
501 return ret;
502 }
503
504 return 0;
505}
506EXPORT_SYMBOL(drm_modeset_lock_all_ctx);