| /* |
| * Copyright (C) 2014 Red Hat |
| * Author: Rob Clark <robdclark@gmail.com> |
| * |
| * Permission is hereby granted, free of charge, to any person obtaining a |
| * copy of this software and associated documentation files (the "Software"), |
| * to deal in the Software without restriction, including without limitation |
| * the rights to use, copy, modify, merge, publish, distribute, sublicense, |
| * and/or sell copies of the Software, and to permit persons to whom the |
| * Software is furnished to do so, subject to the following conditions: |
| * |
| * The above copyright notice and this permission notice shall be included in |
| * all copies or substantial portions of the Software. |
| * |
| * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR |
| * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, |
| * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL |
| * THE COPYRIGHT HOLDER(S) OR AUTHOR(S) BE LIABLE FOR ANY CLAIM, DAMAGES OR |
| * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, |
| * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR |
| * OTHER DEALINGS IN THE SOFTWARE. |
| */ |
| |
| #include <drm/drmP.h> |
| #include <drm/drm_crtc.h> |
| #include <drm/drm_modeset_lock.h> |
| |
| /** |
| * DOC: kms locking |
| * |
| * As KMS moves toward more fine grained locking, and atomic ioctl where |
| * userspace can indirectly control locking order, it becomes necessary |
| * to use &ww_mutex and acquire-contexts to avoid deadlocks. But because |
| * the locking is more distributed around the driver code, we want a bit |
| * of extra utility/tracking out of our acquire-ctx. This is provided |
| * by &struct drm_modeset_lock and &struct drm_modeset_acquire_ctx. |
| * |
| * For basic principles of &ww_mutex, see: Documentation/locking/ww-mutex-design.txt |
| * |
| * The basic usage pattern is to:: |
| * |
| * drm_modeset_acquire_init(ctx, DRM_MODESET_ACQUIRE_INTERRUPTIBLE) |
| * retry: |
| * foreach (lock in random_ordered_set_of_locks) { |
| * ret = drm_modeset_lock(lock, ctx) |
| * if (ret == -EDEADLK) { |
| * ret = drm_modeset_backoff(ctx); |
| * if (!ret) |
| * goto retry; |
| * } |
| * if (ret) |
| * goto out; |
| * } |
| * ... do stuff ... |
| * out: |
| * drm_modeset_drop_locks(ctx); |
| * drm_modeset_acquire_fini(ctx); |
| * |
| * If all that is needed is a single modeset lock, then the &struct |
| * drm_modeset_acquire_ctx is not needed and the locking can be simplified |
| * by passing a NULL instead of ctx in the drm_modeset_lock() call or |
| * calling drm_modeset_lock_single_interruptible(). To unlock afterwards |
| * call drm_modeset_unlock(). |
| * |
| * On top of these per-object locks using &ww_mutex there's also an overall |
| * &drm_mode_config.mutex, for protecting everything else. Mostly this means |
| * probe state of connectors, and preventing hotplug add/removal of connectors. |
| * |
| * Finally there's a bunch of dedicated locks to protect drm core internal |
| * lists and lookup data structures. |
| */ |
| |
| static DEFINE_WW_CLASS(crtc_ww_class); |
| |
| /** |
| * drm_modeset_lock_all - take all modeset locks |
| * @dev: DRM device |
| * |
| * This function takes all modeset locks, suitable where a more fine-grained |
| * scheme isn't (yet) implemented. Locks must be dropped by calling the |
| * drm_modeset_unlock_all() function. |
| * |
| * This function is deprecated. It allocates a lock acquisition context and |
| * stores it in &drm_device.mode_config. This facilitate conversion of |
| * existing code because it removes the need to manually deal with the |
| * acquisition context, but it is also brittle because the context is global |
| * and care must be taken not to nest calls. New code should use the |
| * drm_modeset_lock_all_ctx() function and pass in the context explicitly. |
| */ |
| void drm_modeset_lock_all(struct drm_device *dev) |
| { |
| struct drm_mode_config *config = &dev->mode_config; |
| struct drm_modeset_acquire_ctx *ctx; |
| int ret; |
| |
| ctx = kzalloc(sizeof(*ctx), GFP_KERNEL | __GFP_NOFAIL); |
| if (WARN_ON(!ctx)) |
| return; |
| |
| mutex_lock(&config->mutex); |
| |
| drm_modeset_acquire_init(ctx, 0); |
| |
| retry: |
| ret = drm_modeset_lock_all_ctx(dev, ctx); |
| if (ret < 0) { |
| if (ret == -EDEADLK) { |
| drm_modeset_backoff(ctx); |
| goto retry; |
| } |
| |
| drm_modeset_acquire_fini(ctx); |
| kfree(ctx); |
| return; |
| } |
| |
| WARN_ON(config->acquire_ctx); |
| |
| /* |
| * We hold the locks now, so it is safe to stash the acquisition |
| * context for drm_modeset_unlock_all(). |
| */ |
| config->acquire_ctx = ctx; |
| |
| drm_warn_on_modeset_not_all_locked(dev); |
| } |
| EXPORT_SYMBOL(drm_modeset_lock_all); |
| |
| /** |
| * drm_modeset_unlock_all - drop all modeset locks |
| * @dev: DRM device |
| * |
| * This function drops all modeset locks taken by a previous call to the |
| * drm_modeset_lock_all() function. |
| * |
| * This function is deprecated. It uses the lock acquisition context stored |
| * in &drm_device.mode_config. This facilitates conversion of existing |
| * code because it removes the need to manually deal with the acquisition |
| * context, but it is also brittle because the context is global and care must |
| * be taken not to nest calls. New code should pass the acquisition context |
| * directly to the drm_modeset_drop_locks() function. |
| */ |
| void drm_modeset_unlock_all(struct drm_device *dev) |
| { |
| struct drm_mode_config *config = &dev->mode_config; |
| struct drm_modeset_acquire_ctx *ctx = config->acquire_ctx; |
| |
| if (WARN_ON(!ctx)) |
| return; |
| |
| config->acquire_ctx = NULL; |
| drm_modeset_drop_locks(ctx); |
| drm_modeset_acquire_fini(ctx); |
| |
| kfree(ctx); |
| |
| mutex_unlock(&dev->mode_config.mutex); |
| } |
| EXPORT_SYMBOL(drm_modeset_unlock_all); |
| |
| /** |
| * drm_warn_on_modeset_not_all_locked - check that all modeset locks are locked |
| * @dev: device |
| * |
| * Useful as a debug assert. |
| */ |
| void drm_warn_on_modeset_not_all_locked(struct drm_device *dev) |
| { |
| struct drm_crtc *crtc; |
| |
| /* Locking is currently fubar in the panic handler. */ |
| if (oops_in_progress) |
| return; |
| |
| drm_for_each_crtc(crtc, dev) |
| WARN_ON(!drm_modeset_is_locked(&crtc->mutex)); |
| |
| WARN_ON(!drm_modeset_is_locked(&dev->mode_config.connection_mutex)); |
| WARN_ON(!mutex_is_locked(&dev->mode_config.mutex)); |
| } |
| EXPORT_SYMBOL(drm_warn_on_modeset_not_all_locked); |
| |
| /** |
| * drm_modeset_acquire_init - initialize acquire context |
| * @ctx: the acquire context |
| * @flags: 0 or %DRM_MODESET_ACQUIRE_INTERRUPTIBLE |
| * |
| * When passing %DRM_MODESET_ACQUIRE_INTERRUPTIBLE to @flags, |
| * all calls to drm_modeset_lock() will perform an interruptible |
| * wait. |
| */ |
| void drm_modeset_acquire_init(struct drm_modeset_acquire_ctx *ctx, |
| uint32_t flags) |
| { |
| memset(ctx, 0, sizeof(*ctx)); |
| ww_acquire_init(&ctx->ww_ctx, &crtc_ww_class); |
| INIT_LIST_HEAD(&ctx->locked); |
| |
| if (flags & DRM_MODESET_ACQUIRE_INTERRUPTIBLE) |
| ctx->interruptible = true; |
| } |
| EXPORT_SYMBOL(drm_modeset_acquire_init); |
| |
| /** |
| * drm_modeset_acquire_fini - cleanup acquire context |
| * @ctx: the acquire context |
| */ |
| void drm_modeset_acquire_fini(struct drm_modeset_acquire_ctx *ctx) |
| { |
| ww_acquire_fini(&ctx->ww_ctx); |
| } |
| EXPORT_SYMBOL(drm_modeset_acquire_fini); |
| |
| /** |
| * drm_modeset_drop_locks - drop all locks |
| * @ctx: the acquire context |
| * |
| * Drop all locks currently held against this acquire context. |
| */ |
| void drm_modeset_drop_locks(struct drm_modeset_acquire_ctx *ctx) |
| { |
| WARN_ON(ctx->contended); |
| while (!list_empty(&ctx->locked)) { |
| struct drm_modeset_lock *lock; |
| |
| lock = list_first_entry(&ctx->locked, |
| struct drm_modeset_lock, head); |
| |
| drm_modeset_unlock(lock); |
| } |
| } |
| EXPORT_SYMBOL(drm_modeset_drop_locks); |
| |
| static inline int modeset_lock(struct drm_modeset_lock *lock, |
| struct drm_modeset_acquire_ctx *ctx, |
| bool interruptible, bool slow) |
| { |
| int ret; |
| |
| WARN_ON(ctx->contended); |
| |
| if (ctx->trylock_only) { |
| lockdep_assert_held(&ctx->ww_ctx); |
| |
| if (!ww_mutex_trylock(&lock->mutex)) |
| return -EBUSY; |
| else |
| return 0; |
| } else if (interruptible && slow) { |
| ret = ww_mutex_lock_slow_interruptible(&lock->mutex, &ctx->ww_ctx); |
| } else if (interruptible) { |
| ret = ww_mutex_lock_interruptible(&lock->mutex, &ctx->ww_ctx); |
| } else if (slow) { |
| ww_mutex_lock_slow(&lock->mutex, &ctx->ww_ctx); |
| ret = 0; |
| } else { |
| ret = ww_mutex_lock(&lock->mutex, &ctx->ww_ctx); |
| } |
| if (!ret) { |
| WARN_ON(!list_empty(&lock->head)); |
| list_add(&lock->head, &ctx->locked); |
| } else if (ret == -EALREADY) { |
| /* we already hold the lock.. this is fine. For atomic |
| * we will need to be able to drm_modeset_lock() things |
| * without having to keep track of what is already locked |
| * or not. |
| */ |
| ret = 0; |
| } else if (ret == -EDEADLK) { |
| ctx->contended = lock; |
| } |
| |
| return ret; |
| } |
| |
| /** |
| * drm_modeset_backoff - deadlock avoidance backoff |
| * @ctx: the acquire context |
| * |
| * If deadlock is detected (ie. drm_modeset_lock() returns -EDEADLK), |
| * you must call this function to drop all currently held locks and |
| * block until the contended lock becomes available. |
| * |
| * This function returns 0 on success, or -ERESTARTSYS if this context |
| * is initialized with %DRM_MODESET_ACQUIRE_INTERRUPTIBLE and the |
| * wait has been interrupted. |
| */ |
| int drm_modeset_backoff(struct drm_modeset_acquire_ctx *ctx) |
| { |
| struct drm_modeset_lock *contended = ctx->contended; |
| |
| ctx->contended = NULL; |
| |
| if (WARN_ON(!contended)) |
| return 0; |
| |
| drm_modeset_drop_locks(ctx); |
| |
| return modeset_lock(contended, ctx, ctx->interruptible, true); |
| } |
| EXPORT_SYMBOL(drm_modeset_backoff); |
| |
| /** |
| * drm_modeset_lock_init - initialize lock |
| * @lock: lock to init |
| */ |
| void drm_modeset_lock_init(struct drm_modeset_lock *lock) |
| { |
| ww_mutex_init(&lock->mutex, &crtc_ww_class); |
| INIT_LIST_HEAD(&lock->head); |
| } |
| EXPORT_SYMBOL(drm_modeset_lock_init); |
| |
| /** |
| * drm_modeset_lock - take modeset lock |
| * @lock: lock to take |
| * @ctx: acquire ctx |
| * |
| * If @ctx is not NULL, then its ww acquire context is used and the |
| * lock will be tracked by the context and can be released by calling |
| * drm_modeset_drop_locks(). If -EDEADLK is returned, this means a |
| * deadlock scenario has been detected and it is an error to attempt |
| * to take any more locks without first calling drm_modeset_backoff(). |
| * |
| * If the @ctx is not NULL and initialized with |
| * %DRM_MODESET_ACQUIRE_INTERRUPTIBLE, this function will fail with |
| * -ERESTARTSYS when interrupted. |
| * |
| * If @ctx is NULL then the function call behaves like a normal, |
| * uninterruptible non-nesting mutex_lock() call. |
| */ |
| int drm_modeset_lock(struct drm_modeset_lock *lock, |
| struct drm_modeset_acquire_ctx *ctx) |
| { |
| if (ctx) |
| return modeset_lock(lock, ctx, ctx->interruptible, false); |
| |
| ww_mutex_lock(&lock->mutex, NULL); |
| return 0; |
| } |
| EXPORT_SYMBOL(drm_modeset_lock); |
| |
| /** |
| * drm_modeset_lock_single_interruptible - take a single modeset lock |
| * @lock: lock to take |
| * |
| * This function behaves as drm_modeset_lock() with a NULL context, |
| * but performs interruptible waits. |
| * |
| * This function returns 0 on success, or -ERESTARTSYS when interrupted. |
| */ |
| int drm_modeset_lock_single_interruptible(struct drm_modeset_lock *lock) |
| { |
| return ww_mutex_lock_interruptible(&lock->mutex, NULL); |
| } |
| EXPORT_SYMBOL(drm_modeset_lock_single_interruptible); |
| |
| /** |
| * drm_modeset_unlock - drop modeset lock |
| * @lock: lock to release |
| */ |
| void drm_modeset_unlock(struct drm_modeset_lock *lock) |
| { |
| list_del_init(&lock->head); |
| ww_mutex_unlock(&lock->mutex); |
| } |
| EXPORT_SYMBOL(drm_modeset_unlock); |
| |
| /** |
| * drm_modeset_lock_all_ctx - take all modeset locks |
| * @dev: DRM device |
| * @ctx: lock acquisition context |
| * |
| * This function takes all modeset locks, suitable where a more fine-grained |
| * scheme isn't (yet) implemented. |
| * |
| * Unlike drm_modeset_lock_all(), it doesn't take the &drm_mode_config.mutex |
| * since that lock isn't required for modeset state changes. Callers which |
| * need to grab that lock too need to do so outside of the acquire context |
| * @ctx. |
| * |
| * Locks acquired with this function should be released by calling the |
| * drm_modeset_drop_locks() function on @ctx. |
| * |
| * Returns: 0 on success or a negative error-code on failure. |
| */ |
| int drm_modeset_lock_all_ctx(struct drm_device *dev, |
| struct drm_modeset_acquire_ctx *ctx) |
| { |
| struct drm_crtc *crtc; |
| struct drm_plane *plane; |
| int ret; |
| |
| ret = drm_modeset_lock(&dev->mode_config.connection_mutex, ctx); |
| if (ret) |
| return ret; |
| |
| drm_for_each_crtc(crtc, dev) { |
| ret = drm_modeset_lock(&crtc->mutex, ctx); |
| if (ret) |
| return ret; |
| } |
| |
| drm_for_each_plane(plane, dev) { |
| ret = drm_modeset_lock(&plane->mutex, ctx); |
| if (ret) |
| return ret; |
| } |
| |
| return 0; |
| } |
| EXPORT_SYMBOL(drm_modeset_lock_all_ctx); |