| 1 | /* $NetBSD: drm_lock.c,v 1.4 2016/04/02 22:40:43 riastradh Exp $ */ |
| 2 | |
| 3 | /*- |
| 4 | * Copyright (c) 2013 The NetBSD Foundation, Inc. |
| 5 | * All rights reserved. |
| 6 | * |
| 7 | * This code is derived from software contributed to The NetBSD Foundation |
| 8 | * by Taylor R. Campbell. |
| 9 | * |
| 10 | * Redistribution and use in source and binary forms, with or without |
| 11 | * modification, are permitted provided that the following conditions |
| 12 | * are met: |
| 13 | * 1. Redistributions of source code must retain the above copyright |
| 14 | * notice, this list of conditions and the following disclaimer. |
| 15 | * 2. Redistributions in binary form must reproduce the above copyright |
| 16 | * notice, this list of conditions and the following disclaimer in the |
| 17 | * documentation and/or other materials provided with the distribution. |
| 18 | * |
| 19 | * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS |
| 20 | * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED |
| 21 | * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR |
| 22 | * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS |
| 23 | * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR |
| 24 | * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF |
| 25 | * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS |
| 26 | * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN |
| 27 | * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) |
| 28 | * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE |
| 29 | * POSSIBILITY OF SUCH DAMAGE. |
| 30 | */ |
| 31 | |
| 32 | /* |
| 33 | * DRM lock. Each drm master has a heavy-weight lock to provide mutual |
| 34 | * exclusion for access to the hardware. The lock can be held by the |
| 35 | * kernel or by a drm file; the kernel takes access only for unusual |
| 36 | * purposes, with drm_idlelock_take, mainly for idling the GPU when |
| 37 | * closing down. |
| 38 | * |
| 39 | * The physical memory storing the lock state is shared between |
| 40 | * userland and kernel: the pointer at dev->master->lock->hw_lock is |
| 41 | * mapped into both userland and kernel address spaces. This way, |
| 42 | * userland can try to take the hardware lock without a system call, |
| 43 | * although if it fails then it will use the DRM_LOCK ioctl to block |
| 44 | * atomically until the lock is available. All this means that the |
| 45 | * kernel must use atomic_ops to manage the lock state. |
| 46 | */ |
| 47 | |
| 48 | #include <sys/cdefs.h> |
| 49 | __KERNEL_RCSID(0, "$NetBSD: drm_lock.c,v 1.4 2016/04/02 22:40:43 riastradh Exp $" ); |
| 50 | |
| 51 | #include <sys/types.h> |
| 52 | #include <sys/errno.h> |
| 53 | #include <sys/systm.h> |
| 54 | |
| 55 | #include <drm/drmP.h> |
| 56 | |
| 57 | static bool drm_lock_acquire(struct drm_lock_data *, int); |
| 58 | static void drm_lock_release(struct drm_lock_data *, int); |
| 59 | static int drm_lock_block_signals(struct drm_device *, struct drm_lock *, |
| 60 | struct drm_file *); |
| 61 | static void drm_lock_unblock_signals(struct drm_device *, |
| 62 | struct drm_lock *, struct drm_file *); |
| 63 | |
| 64 | /* |
| 65 | * Take the lock on behalf of userland. |
| 66 | */ |
| 67 | int |
| 68 | drm_lock(struct drm_device *dev, void *data, struct drm_file *file) |
| 69 | { |
| 70 | struct drm_lock *lock_request = data; |
| 71 | struct drm_master *master = file->master; |
| 72 | int error; |
| 73 | |
| 74 | /* Sanitize the drm global mutex bollocks until we get rid of it. */ |
| 75 | KASSERT(mutex_is_locked(&drm_global_mutex)); |
| 76 | mutex_unlock(&drm_global_mutex); |
| 77 | |
| 78 | /* Refuse to lock on behalf of the kernel. */ |
| 79 | if (lock_request->context == DRM_KERNEL_CONTEXT) { |
| 80 | error = -EINVAL; |
| 81 | goto out0; |
| 82 | } |
| 83 | |
| 84 | /* Refuse to set the magic bits. */ |
| 85 | if (lock_request->context != |
| 86 | _DRM_LOCKING_CONTEXT(lock_request->context)) { |
| 87 | error = -EINVAL; |
| 88 | goto out0; |
| 89 | } |
| 90 | |
| 91 | /* Count it in the file and device statistics (XXX why here?). */ |
| 92 | file->lock_count++; |
| 93 | |
| 94 | /* Wait until the hardware lock is gone or we can acquire it. */ |
| 95 | spin_lock(&master->lock.spinlock); |
| 96 | |
| 97 | if (master->lock.user_waiters == UINT32_MAX) { |
| 98 | error = -EBUSY; |
| 99 | goto out1; |
| 100 | } |
| 101 | |
| 102 | master->lock.user_waiters++; |
| 103 | DRM_SPIN_WAIT_UNTIL(error, &master->lock.lock_queue, |
| 104 | &master->lock.spinlock, |
| 105 | ((master->lock.hw_lock == NULL) || |
| 106 | drm_lock_acquire(&master->lock, lock_request->context))); |
| 107 | KASSERT(0 < master->lock.user_waiters); |
| 108 | master->lock.user_waiters--; |
| 109 | if (error) |
| 110 | goto out1; |
| 111 | |
| 112 | /* If the lock is gone, give up. */ |
| 113 | if (master->lock.hw_lock == NULL) { |
| 114 | #if 0 /* XXX Linux sends SIGTERM, but why? */ |
| 115 | mutex_enter(proc_lock); |
| 116 | psignal(curproc, SIGTERM); |
| 117 | mutex_exit(proc_lock); |
| 118 | error = -EINTR; |
| 119 | #else |
| 120 | error = -ENXIO; |
| 121 | #endif |
| 122 | goto out1; |
| 123 | } |
| 124 | |
| 125 | /* Mark the lock as owned by file. */ |
| 126 | master->lock.file_priv = file; |
| 127 | master->lock.lock_time = jiffies; /* XXX Unused? */ |
| 128 | |
| 129 | /* Block signals while the lock is held. */ |
| 130 | error = drm_lock_block_signals(dev, lock_request, file); |
| 131 | if (error) |
| 132 | goto fail2; |
| 133 | |
| 134 | /* Enter the DMA quiescent state if requested and available. */ |
| 135 | /* XXX Drop the spin lock first... */ |
| 136 | if (ISSET(lock_request->flags, _DRM_LOCK_QUIESCENT) && |
| 137 | (dev->driver->dma_quiescent != NULL)) { |
| 138 | error = (*dev->driver->dma_quiescent)(dev); |
| 139 | if (error) |
| 140 | goto fail3; |
| 141 | } |
| 142 | |
| 143 | /* Success! */ |
| 144 | error = 0; |
| 145 | goto out1; |
| 146 | |
| 147 | fail3: drm_lock_unblock_signals(dev, lock_request, file); |
| 148 | fail2: drm_lock_release(&master->lock, lock_request->context); |
| 149 | master->lock.file_priv = NULL; |
| 150 | out1: spin_unlock(&master->lock.spinlock); |
| 151 | out0: mutex_lock(&drm_global_mutex); |
| 152 | return error; |
| 153 | } |
| 154 | |
| 155 | /* |
| 156 | * Try to relinquish a lock that userland thinks it holds, per |
| 157 | * userland's request. Fail if it doesn't actually hold the lock. |
| 158 | */ |
| 159 | int |
| 160 | drm_unlock(struct drm_device *dev, void *data, struct drm_file *file) |
| 161 | { |
| 162 | struct drm_lock *lock_request = data; |
| 163 | struct drm_master *master = file->master; |
| 164 | int error; |
| 165 | |
| 166 | /* Sanitize the drm global mutex bollocks until we get rid of it. */ |
| 167 | KASSERT(mutex_is_locked(&drm_global_mutex)); |
| 168 | mutex_unlock(&drm_global_mutex); |
| 169 | |
| 170 | /* Refuse to unlock on behalf of the kernel. */ |
| 171 | if (lock_request->context == DRM_KERNEL_CONTEXT) { |
| 172 | error = -EINVAL; |
| 173 | goto out0; |
| 174 | } |
| 175 | |
| 176 | /* Lock the internal spin lock to make changes. */ |
| 177 | spin_lock(&master->lock.spinlock); |
| 178 | |
| 179 | /* Make sure it's actually locked. */ |
| 180 | if (!_DRM_LOCK_IS_HELD(master->lock.hw_lock->lock)) { |
| 181 | error = -EINVAL; /* XXX Right error? */ |
| 182 | goto out1; |
| 183 | } |
| 184 | |
| 185 | /* Make sure it's locked in the right context. */ |
| 186 | if (_DRM_LOCKING_CONTEXT(master->lock.hw_lock->lock) != |
| 187 | lock_request->context) { |
| 188 | error = -EACCES; /* XXX Right error? */ |
| 189 | goto out1; |
| 190 | } |
| 191 | |
| 192 | /* Make sure it's locked by us. */ |
| 193 | if (master->lock.file_priv != file) { |
| 194 | error = -EACCES; /* XXX Right error? */ |
| 195 | goto out1; |
| 196 | } |
| 197 | |
| 198 | /* Actually release the lock. */ |
| 199 | drm_lock_release(&master->lock, lock_request->context); |
| 200 | |
| 201 | /* Clear the lock's file pointer, just in case. */ |
| 202 | master->lock.file_priv = NULL; |
| 203 | |
| 204 | /* Unblock the signals we blocked in drm_lock. */ |
| 205 | drm_lock_unblock_signals(dev, lock_request, file); |
| 206 | |
| 207 | /* Success! */ |
| 208 | error = 0; |
| 209 | |
| 210 | out1: spin_unlock(&master->lock.spinlock); |
| 211 | out0: mutex_lock(&drm_global_mutex); |
| 212 | return error; |
| 213 | } |
| 214 | |
| 215 | /* |
| 216 | * Drop the lock. |
| 217 | * |
| 218 | * Return value is an artefact of Linux. Caller must guarantee |
| 219 | * preconditions; failure is fatal. |
| 220 | * |
| 221 | * XXX Should we also unblock signals like drm_unlock does? |
| 222 | */ |
| 223 | int |
| 224 | drm_lock_free(struct drm_lock_data *lock_data, unsigned int context) |
| 225 | { |
| 226 | |
| 227 | spin_lock(&lock_data->spinlock); |
| 228 | drm_lock_release(lock_data, context); |
| 229 | spin_unlock(&lock_data->spinlock); |
| 230 | |
| 231 | return 0; |
| 232 | } |
| 233 | |
| 234 | /* |
| 235 | * Try to acquire the lock. Whether or not we acquire it, guarantee |
| 236 | * that whoever next releases it relinquishes it to the kernel, not to |
| 237 | * anyone else. |
| 238 | */ |
| 239 | void |
| 240 | drm_idlelock_take(struct drm_lock_data *lock_data) |
| 241 | { |
| 242 | |
| 243 | spin_lock(&lock_data->spinlock); |
| 244 | KASSERT(!lock_data->idle_has_lock); |
| 245 | KASSERT(lock_data->kernel_waiters < UINT32_MAX); |
| 246 | lock_data->kernel_waiters++; |
| 247 | /* Try to acquire the lock. */ |
| 248 | if (drm_lock_acquire(lock_data, DRM_KERNEL_CONTEXT)) { |
| 249 | lock_data->idle_has_lock = 1; |
| 250 | } else { |
| 251 | /* |
| 252 | * Recording that there are kernel waiters will prevent |
| 253 | * userland from acquiring the lock again when it is |
| 254 | * next released. |
| 255 | */ |
| 256 | } |
| 257 | spin_unlock(&lock_data->spinlock); |
| 258 | } |
| 259 | |
| 260 | /* |
| 261 | * Release whatever drm_idlelock_take managed to acquire. |
| 262 | */ |
| 263 | void |
| 264 | drm_idlelock_release(struct drm_lock_data *lock_data) |
| 265 | { |
| 266 | |
| 267 | spin_lock(&lock_data->spinlock); |
| 268 | KASSERT(0 < lock_data->kernel_waiters); |
| 269 | if (--lock_data->kernel_waiters == 0) { |
| 270 | if (lock_data->idle_has_lock) { |
| 271 | /* We did acquire it. Release it. */ |
| 272 | drm_lock_release(lock_data, DRM_KERNEL_CONTEXT); |
| 273 | } |
| 274 | } |
| 275 | spin_unlock(&lock_data->spinlock); |
| 276 | } |
| 277 | |
| 278 | /* |
| 279 | * Does this file hold this drm device's hardware lock? |
| 280 | * |
| 281 | * Used to decide whether to release the lock when the file is being |
| 282 | * closed. |
| 283 | * |
| 284 | * XXX I don't think this answers correctly in the case that the |
| 285 | * userland has taken the lock and it is uncontended. But I don't |
| 286 | * think we can know what the correct answer is in that case. |
| 287 | */ |
| 288 | int |
| 289 | drm_i_have_hw_lock(struct drm_device *dev, struct drm_file *file) |
| 290 | { |
| 291 | struct drm_lock_data *const lock_data = &file->master->lock; |
| 292 | int answer = 0; |
| 293 | |
| 294 | /* If this file has never locked anything, then no. */ |
| 295 | if (file->lock_count == 0) |
| 296 | return 0; |
| 297 | |
| 298 | spin_lock(&lock_data->spinlock); |
| 299 | |
| 300 | /* If there is no lock, then this file doesn't hold it. */ |
| 301 | if (lock_data->hw_lock == NULL) |
| 302 | goto out; |
| 303 | |
| 304 | /* If this lock is not held, then this file doesn't hold it. */ |
| 305 | if (!_DRM_LOCK_IS_HELD(lock_data->hw_lock->lock)) |
| 306 | goto out; |
| 307 | |
| 308 | /* |
| 309 | * Otherwise, it boils down to whether this file is the owner |
| 310 | * or someone else. |
| 311 | * |
| 312 | * XXX This is not reliable! Userland doesn't update this when |
| 313 | * it takes the lock... |
| 314 | */ |
| 315 | answer = (file == lock_data->file_priv); |
| 316 | |
| 317 | out: spin_unlock(&lock_data->spinlock); |
| 318 | return answer; |
| 319 | } |
| 320 | |
| 321 | /* |
| 322 | * Try to acquire the lock. Return true if successful, false if not. |
| 323 | * |
| 324 | * This is hairy because it races with userland, and if userland |
| 325 | * already holds the lock, we must tell it, by marking it |
| 326 | * _DRM_LOCK_CONT (contended), that it must call ioctl(DRM_UNLOCK) to |
| 327 | * release the lock so that we can wake waiters. |
| 328 | * |
| 329 | * XXX What happens if the process is interrupted? |
| 330 | */ |
| 331 | static bool |
| 332 | drm_lock_acquire(struct drm_lock_data *lock_data, int context) |
| 333 | { |
| 334 | volatile unsigned int *const lock = &lock_data->hw_lock->lock; |
| 335 | unsigned int old, new; |
| 336 | |
| 337 | KASSERT(spin_is_locked(&lock_data->spinlock)); |
| 338 | |
| 339 | do { |
| 340 | old = *lock; |
| 341 | if (!_DRM_LOCK_IS_HELD(old)) { |
| 342 | new = (context | _DRM_LOCK_HELD); |
| 343 | if ((0 < lock_data->user_waiters) || |
| 344 | (0 < lock_data->kernel_waiters)) |
| 345 | new |= _DRM_LOCK_CONT; |
| 346 | } else if (_DRM_LOCKING_CONTEXT(old) != context) { |
| 347 | new = (old | _DRM_LOCK_CONT); |
| 348 | } else { |
| 349 | DRM_ERROR("%d already holds heavyweight lock\n" , |
| 350 | context); |
| 351 | return false; |
| 352 | } |
| 353 | } while (atomic_cas_uint(lock, old, new) != old); |
| 354 | |
| 355 | return !_DRM_LOCK_IS_HELD(old); |
| 356 | } |
| 357 | |
| 358 | /* |
| 359 | * Release the lock held in the given context. Wake any waiters, |
| 360 | * preferring kernel waiters over userland waiters. |
| 361 | * |
| 362 | * Lock's spinlock must be held and lock must be held in this context. |
| 363 | */ |
| 364 | static void |
| 365 | drm_lock_release(struct drm_lock_data *lock_data, int context) |
| 366 | { |
| 367 | |
| 368 | (void)context; /* ignore */ |
| 369 | KASSERT(spin_is_locked(&lock_data->spinlock)); |
| 370 | KASSERT(_DRM_LOCK_IS_HELD(lock_data->hw_lock->lock)); |
| 371 | KASSERT(_DRM_LOCKING_CONTEXT(lock_data->hw_lock->lock) == context); |
| 372 | |
| 373 | lock_data->hw_lock->lock = 0; |
| 374 | DRM_SPIN_WAKEUP_ONE(&lock_data->lock_queue, &lock_data->spinlock); |
| 375 | } |
| 376 | |
| 377 | /* |
| 378 | * Block signals for a process that holds a drm lock. |
| 379 | * |
| 380 | * XXX It's not processes but files that hold drm locks, so blocking |
| 381 | * signals in a process seems wrong, and it's not clear that blocking |
| 382 | * signals automatically is remotely sensible anyway. |
| 383 | */ |
| 384 | static int |
| 385 | drm_lock_block_signals(struct drm_device *dev __unused, |
| 386 | struct drm_lock *lock_request __unused, struct drm_file *file __unused) |
| 387 | { |
| 388 | return 0; |
| 389 | } |
| 390 | |
| 391 | /* |
| 392 | * Unblock the signals that drm_lock_block_signals blocked. |
| 393 | */ |
| 394 | static void |
| 395 | drm_lock_unblock_signals(struct drm_device *dev __unused, |
| 396 | struct drm_lock *lock_request __unused, struct drm_file *file __unused) |
| 397 | { |
| 398 | } |
| 399 | |