drivers/gpu/drm/drm_modeset_lock.c

   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);