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(store: entries, ARRAY_SIZE(entries), skipnr: 1);
88
89 return stack_depot_save(entries, nr_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_debug_printer(prefix: "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(handle: stack_depot, entries: &entries);
104 stack_trace_snprint(buf, PAGE_SIZE, entries, nr_entries, spaces: 2);
105
106 drm_printf(p: &p, f: "attempting to lock a contended lock without backoff:\n%s", buf);
107
108 kfree(objp: 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(size: 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, flags: 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(objp: ctx);
167 return;
168 }
169 ww_acquire_done(ctx: &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(objp: ctx);
210
211 mutex_unlock(lock: &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: &ctx->ww_ctx, ww_class: &crtc_ww_class);
251 INIT_LIST_HEAD(list: &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: &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(stack_depot: ctx->stack_depot);
278
279 while (!list_empty(head: &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(stack_depot: ctx->stack_depot);
298
299 if (ctx->trylock_only) {
300 lockdep_assert_held(&ctx->ww_ctx);
301
302 if (!ww_mutex_trylock(lock: &lock->mutex, NULL))
303 return -EBUSY;
304 else
305 return 0;
306 } else if (interruptible && slow) {
307 ret = ww_mutex_lock_slow_interruptible(lock: &lock->mutex, ctx: &ctx->ww_ctx);
308 } else if (interruptible) {
309 ret = ww_mutex_lock_interruptible(lock: &lock->mutex, ctx: &ctx->ww_ctx);
310 } else if (slow) {
311 ww_mutex_lock_slow(lock: &lock->mutex, ctx: &ctx->ww_ctx);
312 ret = 0;
313 } else {
314 ret = ww_mutex_lock(lock: &lock->mutex, ctx: &ctx->ww_ctx);
315 }
316 if (!ret) {
317 WARN_ON(!list_empty(&lock->head));
318 list_add(new: &lock->head, 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(lock: contended, ctx, interruptible: ctx->interruptible, slow: 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: &lock->mutex, ww_class: &crtc_ww_class);
369 INIT_LIST_HEAD(list: &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, interruptible: ctx->interruptible, slow: false);
397
398 ww_mutex_lock(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: &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(entry: &lock->head);
425 ww_mutex_unlock(lock: &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);
482

source code of linux/drivers/gpu/drm/drm_modeset_lock.c