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51fd371b RC |
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/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 | * | |
52 | * ... do stuff ... | |
53 | * | |
54 | * drm_modeset_drop_locks(&ctx); | |
55 | * drm_modeset_acquire_fini(&ctx); | |
56 | */ | |
57 | ||
58 | ||
59 | /** | |
60 | * drm_modeset_acquire_init - initialize acquire context | |
61 | * @ctx: the acquire context | |
62 | * @flags: for future | |
63 | */ | |
64 | void drm_modeset_acquire_init(struct drm_modeset_acquire_ctx *ctx, | |
65 | uint32_t flags) | |
66 | { | |
67 | ww_acquire_init(&ctx->ww_ctx, &crtc_ww_class); | |
68 | INIT_LIST_HEAD(&ctx->locked); | |
69 | } | |
70 | EXPORT_SYMBOL(drm_modeset_acquire_init); | |
71 | ||
72 | /** | |
73 | * drm_modeset_acquire_fini - cleanup acquire context | |
74 | * @ctx: the acquire context | |
75 | */ | |
76 | void drm_modeset_acquire_fini(struct drm_modeset_acquire_ctx *ctx) | |
77 | { | |
78 | ww_acquire_fini(&ctx->ww_ctx); | |
79 | } | |
80 | EXPORT_SYMBOL(drm_modeset_acquire_fini); | |
81 | ||
82 | /** | |
83 | * drm_modeset_drop_locks - drop all locks | |
84 | * @ctx: the acquire context | |
85 | * | |
86 | * Drop all locks currently held against this acquire context. | |
87 | */ | |
88 | void drm_modeset_drop_locks(struct drm_modeset_acquire_ctx *ctx) | |
89 | { | |
90 | WARN_ON(ctx->contended); | |
91 | while (!list_empty(&ctx->locked)) { | |
92 | struct drm_modeset_lock *lock; | |
93 | ||
94 | lock = list_first_entry(&ctx->locked, | |
95 | struct drm_modeset_lock, head); | |
96 | ||
97 | drm_modeset_unlock(lock); | |
98 | } | |
99 | } | |
100 | EXPORT_SYMBOL(drm_modeset_drop_locks); | |
101 | ||
102 | static inline int modeset_lock(struct drm_modeset_lock *lock, | |
103 | struct drm_modeset_acquire_ctx *ctx, | |
104 | bool interruptible, bool slow) | |
105 | { | |
106 | int ret; | |
107 | ||
108 | WARN_ON(ctx->contended); | |
109 | ||
110 | if (interruptible && slow) { | |
111 | ret = ww_mutex_lock_slow_interruptible(&lock->mutex, &ctx->ww_ctx); | |
112 | } else if (interruptible) { | |
113 | ret = ww_mutex_lock_interruptible(&lock->mutex, &ctx->ww_ctx); | |
114 | } else if (slow) { | |
115 | ww_mutex_lock_slow(&lock->mutex, &ctx->ww_ctx); | |
116 | ret = 0; | |
117 | } else { | |
118 | ret = ww_mutex_lock(&lock->mutex, &ctx->ww_ctx); | |
119 | } | |
120 | if (!ret) { | |
121 | WARN_ON(!list_empty(&lock->head)); | |
122 | list_add(&lock->head, &ctx->locked); | |
123 | } else if (ret == -EALREADY) { | |
124 | /* we already hold the lock.. this is fine. For atomic | |
125 | * we will need to be able to drm_modeset_lock() things | |
126 | * without having to keep track of what is already locked | |
127 | * or not. | |
128 | */ | |
129 | ret = 0; | |
130 | } else if (ret == -EDEADLK) { | |
131 | ctx->contended = lock; | |
132 | } | |
133 | ||
134 | return ret; | |
135 | } | |
136 | ||
137 | static int modeset_backoff(struct drm_modeset_acquire_ctx *ctx, | |
138 | bool interruptible) | |
139 | { | |
140 | struct drm_modeset_lock *contended = ctx->contended; | |
141 | ||
142 | ctx->contended = NULL; | |
143 | ||
144 | if (WARN_ON(!contended)) | |
145 | return 0; | |
146 | ||
147 | drm_modeset_drop_locks(ctx); | |
148 | ||
149 | return modeset_lock(contended, ctx, interruptible, true); | |
150 | } | |
151 | ||
152 | /** | |
153 | * drm_modeset_backoff - deadlock avoidance backoff | |
154 | * @ctx: the acquire context | |
155 | * | |
156 | * If deadlock is detected (ie. drm_modeset_lock() returns -EDEADLK), | |
157 | * you must call this function to drop all currently held locks and | |
158 | * block until the contended lock becomes available. | |
159 | */ | |
160 | void drm_modeset_backoff(struct drm_modeset_acquire_ctx *ctx) | |
161 | { | |
162 | modeset_backoff(ctx, false); | |
163 | } | |
164 | EXPORT_SYMBOL(drm_modeset_backoff); | |
165 | ||
166 | /** | |
167 | * drm_modeset_backoff_interruptible - deadlock avoidance backoff | |
168 | * @ctx: the acquire context | |
169 | * | |
170 | * Interruptible version of drm_modeset_backoff() | |
171 | */ | |
172 | int drm_modeset_backoff_interruptible(struct drm_modeset_acquire_ctx *ctx) | |
173 | { | |
174 | return modeset_backoff(ctx, true); | |
175 | } | |
176 | EXPORT_SYMBOL(drm_modeset_backoff_interruptible); | |
177 | ||
178 | /** | |
179 | * drm_modeset_lock - take modeset lock | |
180 | * @lock: lock to take | |
181 | * @ctx: acquire ctx | |
182 | * | |
183 | * If ctx is not NULL, then its ww acquire context is used and the | |
184 | * lock will be tracked by the context and can be released by calling | |
185 | * drm_modeset_drop_locks(). If -EDEADLK is returned, this means a | |
186 | * deadlock scenario has been detected and it is an error to attempt | |
187 | * to take any more locks without first calling drm_modeset_backoff(). | |
188 | */ | |
189 | int drm_modeset_lock(struct drm_modeset_lock *lock, | |
190 | struct drm_modeset_acquire_ctx *ctx) | |
191 | { | |
192 | if (ctx) | |
193 | return modeset_lock(lock, ctx, false, false); | |
194 | ||
195 | ww_mutex_lock(&lock->mutex, NULL); | |
196 | return 0; | |
197 | } | |
198 | EXPORT_SYMBOL(drm_modeset_lock); | |
199 | ||
200 | /** | |
201 | * drm_modeset_lock_interruptible - take modeset lock | |
202 | * @lock: lock to take | |
203 | * @ctx: acquire ctx | |
204 | * | |
205 | * Interruptible version of drm_modeset_lock() | |
206 | */ | |
207 | int drm_modeset_lock_interruptible(struct drm_modeset_lock *lock, | |
208 | struct drm_modeset_acquire_ctx *ctx) | |
209 | { | |
210 | if (ctx) | |
211 | return modeset_lock(lock, ctx, true, false); | |
212 | ||
213 | return ww_mutex_lock_interruptible(&lock->mutex, NULL); | |
214 | } | |
215 | EXPORT_SYMBOL(drm_modeset_lock_interruptible); | |
216 | ||
217 | /** | |
218 | * drm_modeset_unlock - drop modeset lock | |
219 | * @lock: lock to release | |
220 | */ | |
221 | void drm_modeset_unlock(struct drm_modeset_lock *lock) | |
222 | { | |
223 | list_del_init(&lock->head); | |
224 | ww_mutex_unlock(&lock->mutex); | |
225 | } | |
226 | EXPORT_SYMBOL(drm_modeset_unlock); | |
227 | ||
228 | /* Temporary.. until we have sufficiently fine grained locking, there | |
229 | * are a couple scenarios where it is convenient to grab all crtc locks. | |
230 | * It is planned to remove this: | |
231 | */ | |
232 | int drm_modeset_lock_all_crtcs(struct drm_device *dev, | |
233 | struct drm_modeset_acquire_ctx *ctx) | |
234 | { | |
235 | struct drm_mode_config *config = &dev->mode_config; | |
236 | struct drm_crtc *crtc; | |
237 | int ret = 0; | |
238 | ||
239 | list_for_each_entry(crtc, &config->crtc_list, head) { | |
240 | ret = drm_modeset_lock(&crtc->mutex, ctx); | |
241 | if (ret) | |
242 | return ret; | |
243 | } | |
244 | ||
245 | return 0; | |
246 | } | |
247 | EXPORT_SYMBOL(drm_modeset_lock_all_crtcs); |