Differential D23085 Diff 66487 sys/dev/drm/core/drm_modeset_lock.c

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sys/dev/drm/core/drm_modeset_lock.c

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				/*
				* 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/drm_atomic.h>
				#include <drm/drm_crtc.h>
				#include <drm/drm_device.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.rst
				*
				* 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);
				*
				* For convenience this control flow is implemented in
				* DRM_MODESET_LOCK_ALL_BEGIN() and DRM_MODESET_LOCK_ALL_END() for the case
				* where all modeset locks need to be taken through drm_modeset_lock_all_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;
				}
				ww_acquire_done(&ctx->ww_ctx);

				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) {
				#ifdef __linux__
				lockdep_assert_held(&ctx->ww_ctx);
				#endif

				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.
				*
				* See also: DRM_MODESET_LOCK_ALL_BEGIN() and DRM_MODESET_LOCK_ALL_END()
				*
				* 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_private_obj *privobj;
				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;
				}

				drm_for_each_privobj(privobj, dev) {
				ret = drm_modeset_lock(&privobj->lock, ctx);
				if (ret)
				return ret;
				}

				return 0;
				}
				EXPORT_SYMBOL(drm_modeset_lock_all_ctx);