drm_modeset_lock.c | Explore in Territory

/*
 * Copyright (C) 2014 Red Hat
 * Author: Rob Clark <[email protected]>
 *
 * 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>
#include <drm/drm_print.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);

#if IS_ENABLED(CONFIG_DRM_DEBUG_MODESET_LOCK)
static noinline depot_stack_handle_t __drm_stack_depot_save(void)
{ … }

static void __drm_stack_depot_print(depot_stack_handle_t stack_depot)
{ … }

static void __drm_stack_depot_init(void)
{ … }
#else /* CONFIG_DRM_DEBUG_MODESET_LOCK */
static depot_stack_handle_t __drm_stack_depot_save(void)
{
	return 0;
}
static void __drm_stack_depot_print(depot_stack_handle_t stack_depot)
{
}
static void __drm_stack_depot_init(void)
{
}
#endif /* CONFIG_DRM_DEBUG_MODESET_LOCK */

/**
 * 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)
{ … }
EXPORT_SYMBOL(…);

/**
 * 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)
{ … }
EXPORT_SYMBOL(…);

/**
 * 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)
{ … }
EXPORT_SYMBOL(…);

/**
 * 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)
{ … }
EXPORT_SYMBOL(…);

/**
 * drm_modeset_acquire_fini - cleanup acquire context
 * @ctx: the acquire context
 */
void drm_modeset_acquire_fini(struct drm_modeset_acquire_ctx *ctx)
{ … }
EXPORT_SYMBOL(…);

/**
 * 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)
{ … }
EXPORT_SYMBOL(…);

static inline int modeset_lock(struct drm_modeset_lock *lock,
		struct drm_modeset_acquire_ctx *ctx,
		bool interruptible, bool slow)
{ … }

/**
 * 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)
{ … }
EXPORT_SYMBOL(…);

/**
 * drm_modeset_lock_init - initialize lock
 * @lock: lock to init
 */
void drm_modeset_lock_init(struct drm_modeset_lock *lock)
{ … }
EXPORT_SYMBOL(…);

/**
 * 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)
{ … }
EXPORT_SYMBOL(…);

/**
 * 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)
{ … }
EXPORT_SYMBOL(…);

/**
 * drm_modeset_unlock - drop modeset lock
 * @lock: lock to release
 */
void drm_modeset_unlock(struct drm_modeset_lock *lock)
{ … }
EXPORT_SYMBOL(…);

/**
 * 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)
{ … }
EXPORT_SYMBOL(…);
linux/drivers/gpu/drm/drm_modeset_lock.c
