/*
* 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)
* retry:
* foreach (lock in random_ordered_set_of_locks) {
* ret = drm_modeset_lock(lock, &ctx)
* if (ret == -EDEADLK) {
* drm_modeset_backoff(&ctx);
* goto retry;
* }
* }
* ... do stuff ...
* 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 and, when done, by calling 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);
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: for future
*/
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);
}
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;
}
static int modeset_backoff(struct drm_modeset_acquire_ctx *ctx,
bool interruptible)
{
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, interruptible, true);
}
/**
* 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.
*/
void drm_modeset_backoff(struct drm_modeset_acquire_ctx *ctx)
{
modeset_backoff(ctx, false);
}
EXPORT_SYMBOL(drm_modeset_backoff);
/**
* drm_modeset_backoff_interruptible - deadlock avoidance backoff
* @ctx: the acquire context
*
* Interruptible version of drm_modeset_backoff()
*/
int drm_modeset_backoff_interruptible(struct drm_modeset_acquire_ctx *ctx)
{
return modeset_backoff(ctx, true);
}
EXPORT_SYMBOL(drm_modeset_backoff_interruptible);
/**
* 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 @ctx is NULL then the function call behaves like a normal,
* 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, false, false);
ww_mutex_lock(&lock->mutex, NULL);
return 0;
}
EXPORT_SYMBOL(drm_modeset_lock);
/**
* drm_modeset_lock_interruptible - take modeset lock
* @lock: lock to take
* @ctx: acquire ctx
*
* Interruptible version of drm_modeset_lock()
*/
int drm_modeset_lock_interruptible(struct drm_modeset_lock *lock,
struct drm_modeset_acquire_ctx *ctx)
{
if (ctx)
return modeset_lock(lock, ctx, true, false);
return ww_mutex_lock_interruptible(&lock->mutex, NULL);
}
EXPORT_SYMBOL(drm_modeset_lock_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);
