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); 248