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 memset(ctx, 0, sizeof(*ctx)); 68 ww_acquire_init(&ctx->ww_ctx, &crtc_ww_class); 69 INIT_LIST_HEAD(&ctx->locked); 70 } 71 EXPORT_SYMBOL(drm_modeset_acquire_init); 72 73 /** 74 * drm_modeset_acquire_fini - cleanup acquire context 75 * @ctx: the acquire context 76 */ 77 void drm_modeset_acquire_fini(struct drm_modeset_acquire_ctx *ctx) 78 { 79 ww_acquire_fini(&ctx->ww_ctx); 80 } 81 EXPORT_SYMBOL(drm_modeset_acquire_fini); 82 83 /** 84 * drm_modeset_drop_locks - drop all locks 85 * @ctx: the acquire context 86 * 87 * Drop all locks currently held against this acquire context. 88 */ 89 void drm_modeset_drop_locks(struct drm_modeset_acquire_ctx *ctx) 90 { 91 WARN_ON(ctx->contended); 92 while (!list_empty(&ctx->locked)) { 93 struct drm_modeset_lock *lock; 94 95 lock = list_first_entry(&ctx->locked, 96 struct drm_modeset_lock, head); 97 98 drm_modeset_unlock(lock); 99 } 100 } 101 EXPORT_SYMBOL(drm_modeset_drop_locks); 102 103 static inline int modeset_lock(struct drm_modeset_lock *lock, 104 struct drm_modeset_acquire_ctx *ctx, 105 bool interruptible, bool slow) 106 { 107 int ret; 108 109 WARN_ON(ctx->contended); 110 111 if (interruptible && slow) { 112 ret = ww_mutex_lock_slow_interruptible(&lock->mutex, &ctx->ww_ctx); 113 } else if (interruptible) { 114 ret = ww_mutex_lock_interruptible(&lock->mutex, &ctx->ww_ctx); 115 } else if (slow) { 116 ww_mutex_lock_slow(&lock->mutex, &ctx->ww_ctx); 117 ret = 0; 118 } else { 119 ret = ww_mutex_lock(&lock->mutex, &ctx->ww_ctx); 120 } 121 if (!ret) { 122 WARN_ON(!list_empty(&lock->head)); 123 list_add(&lock->head, &ctx->locked); 124 } else if (ret == -EALREADY) { 125 /* we already hold the lock.. this is fine. For atomic 126 * we will need to be able to drm_modeset_lock() things 127 * without having to keep track of what is already locked 128 * or not. 129 */ 130 ret = 0; 131 } else if (ret == -EDEADLK) { 132 ctx->contended = lock; 133 } 134 135 return ret; 136 } 137 138 static int modeset_backoff(struct drm_modeset_acquire_ctx *ctx, 139 bool interruptible) 140 { 141 struct drm_modeset_lock *contended = ctx->contended; 142 143 ctx->contended = NULL; 144 145 if (WARN_ON(!contended)) 146 return 0; 147 148 drm_modeset_drop_locks(ctx); 149 150 return modeset_lock(contended, ctx, interruptible, true); 151 } 152 153 /** 154 * drm_modeset_backoff - deadlock avoidance backoff 155 * @ctx: the acquire context 156 * 157 * If deadlock is detected (ie. drm_modeset_lock() returns -EDEADLK), 158 * you must call this function to drop all currently held locks and 159 * block until the contended lock becomes available. 160 */ 161 void drm_modeset_backoff(struct drm_modeset_acquire_ctx *ctx) 162 { 163 modeset_backoff(ctx, false); 164 } 165 EXPORT_SYMBOL(drm_modeset_backoff); 166 167 /** 168 * drm_modeset_backoff_interruptible - deadlock avoidance backoff 169 * @ctx: the acquire context 170 * 171 * Interruptible version of drm_modeset_backoff() 172 */ 173 int drm_modeset_backoff_interruptible(struct drm_modeset_acquire_ctx *ctx) 174 { 175 return modeset_backoff(ctx, true); 176 } 177 EXPORT_SYMBOL(drm_modeset_backoff_interruptible); 178 179 /** 180 * drm_modeset_lock - take modeset lock 181 * @lock: lock to take 182 * @ctx: acquire ctx 183 * 184 * If ctx is not NULL, then its ww acquire context is used and the 185 * lock will be tracked by the context and can be released by calling 186 * drm_modeset_drop_locks(). If -EDEADLK is returned, this means a 187 * deadlock scenario has been detected and it is an error to attempt 188 * to take any more locks without first calling drm_modeset_backoff(). 189 */ 190 int drm_modeset_lock(struct drm_modeset_lock *lock, 191 struct drm_modeset_acquire_ctx *ctx) 192 { 193 if (ctx) 194 return modeset_lock(lock, ctx, false, false); 195 196 ww_mutex_lock(&lock->mutex, NULL); 197 return 0; 198 } 199 EXPORT_SYMBOL(drm_modeset_lock); 200 201 /** 202 * drm_modeset_lock_interruptible - take modeset lock 203 * @lock: lock to take 204 * @ctx: acquire ctx 205 * 206 * Interruptible version of drm_modeset_lock() 207 */ 208 int drm_modeset_lock_interruptible(struct drm_modeset_lock *lock, 209 struct drm_modeset_acquire_ctx *ctx) 210 { 211 if (ctx) 212 return modeset_lock(lock, ctx, true, false); 213 214 return ww_mutex_lock_interruptible(&lock->mutex, NULL); 215 } 216 EXPORT_SYMBOL(drm_modeset_lock_interruptible); 217 218 /** 219 * drm_modeset_unlock - drop modeset lock 220 * @lock: lock to release 221 */ 222 void drm_modeset_unlock(struct drm_modeset_lock *lock) 223 { 224 list_del_init(&lock->head); 225 ww_mutex_unlock(&lock->mutex); 226 } 227 EXPORT_SYMBOL(drm_modeset_unlock); 228 229 /* Temporary.. until we have sufficiently fine grained locking, there 230 * are a couple scenarios where it is convenient to grab all crtc locks. 231 * It is planned to remove this: 232 */ 233 int drm_modeset_lock_all_crtcs(struct drm_device *dev, 234 struct drm_modeset_acquire_ctx *ctx) 235 { 236 struct drm_mode_config *config = &dev->mode_config; 237 struct drm_crtc *crtc; 238 int ret = 0; 239 240 list_for_each_entry(crtc, &config->crtc_list, head) { 241 ret = drm_modeset_lock(&crtc->mutex, ctx); 242 if (ret) 243 return ret; 244 } 245 246 return 0; 247 } 248 EXPORT_SYMBOL(drm_modeset_lock_all_crtcs); 249