249 lines
6.9 KiB
C
249 lines
6.9 KiB
C
/*
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* Copyright (C) 2014 Red Hat
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* Author: Rob Clark <robdclark@gmail.com>
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*
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* Permission is hereby granted, free of charge, to any person obtaining a
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* copy of this software and associated documentation files (the "Software"),
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* to deal in the Software without restriction, including without limitation
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* the rights to use, copy, modify, merge, publish, distribute, sublicense,
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* and/or sell copies of the Software, and to permit persons to whom the
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* Software is furnished to do so, subject to the following conditions:
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*
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* The above copyright notice and this permission notice shall be included in
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* all copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
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* THE COPYRIGHT HOLDER(S) OR AUTHOR(S) BE LIABLE FOR ANY CLAIM, DAMAGES OR
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* OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
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* ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
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* OTHER DEALINGS IN THE SOFTWARE.
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*/
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#include <drm/drmP.h>
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#include <drm/drm_crtc.h>
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#include <drm/drm_modeset_lock.h>
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/**
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* DOC: kms locking
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*
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* As KMS moves toward more fine grained locking, and atomic ioctl where
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* userspace can indirectly control locking order, it becomes necessary
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* to use ww_mutex and acquire-contexts to avoid deadlocks. But because
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* the locking is more distributed around the driver code, we want a bit
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* of extra utility/tracking out of our acquire-ctx. This is provided
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* by drm_modeset_lock / drm_modeset_acquire_ctx.
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*
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* For basic principles of ww_mutex, see: Documentation/ww-mutex-design.txt
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*
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* The basic usage pattern is to:
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*
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* drm_modeset_acquire_init(&ctx)
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* retry:
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* foreach (lock in random_ordered_set_of_locks) {
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* ret = drm_modeset_lock(lock, &ctx)
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* if (ret == -EDEADLK) {
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* drm_modeset_backoff(&ctx);
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* goto retry;
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* }
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* }
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*
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* ... do stuff ...
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*
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* drm_modeset_drop_locks(&ctx);
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* drm_modeset_acquire_fini(&ctx);
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*/
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/**
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* drm_modeset_acquire_init - initialize acquire context
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* @ctx: the acquire context
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* @flags: for future
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*/
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void drm_modeset_acquire_init(struct drm_modeset_acquire_ctx *ctx,
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uint32_t flags)
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{
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memset(ctx, 0, sizeof(*ctx));
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ww_acquire_init(&ctx->ww_ctx, &crtc_ww_class);
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INIT_LIST_HEAD(&ctx->locked);
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}
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EXPORT_SYMBOL(drm_modeset_acquire_init);
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/**
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* drm_modeset_acquire_fini - cleanup acquire context
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* @ctx: the acquire context
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*/
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void drm_modeset_acquire_fini(struct drm_modeset_acquire_ctx *ctx)
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{
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ww_acquire_fini(&ctx->ww_ctx);
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}
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EXPORT_SYMBOL(drm_modeset_acquire_fini);
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/**
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* drm_modeset_drop_locks - drop all locks
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* @ctx: the acquire context
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*
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* Drop all locks currently held against this acquire context.
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*/
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void drm_modeset_drop_locks(struct drm_modeset_acquire_ctx *ctx)
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{
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WARN_ON(ctx->contended);
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while (!list_empty(&ctx->locked)) {
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struct drm_modeset_lock *lock;
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lock = list_first_entry(&ctx->locked,
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struct drm_modeset_lock, head);
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drm_modeset_unlock(lock);
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}
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}
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EXPORT_SYMBOL(drm_modeset_drop_locks);
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static inline int modeset_lock(struct drm_modeset_lock *lock,
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struct drm_modeset_acquire_ctx *ctx,
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bool interruptible, bool slow)
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{
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int ret;
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WARN_ON(ctx->contended);
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if (interruptible && slow) {
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ret = ww_mutex_lock_slow_interruptible(&lock->mutex, &ctx->ww_ctx);
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} else if (interruptible) {
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ret = ww_mutex_lock_interruptible(&lock->mutex, &ctx->ww_ctx);
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} else if (slow) {
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ww_mutex_lock_slow(&lock->mutex, &ctx->ww_ctx);
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ret = 0;
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} else {
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ret = ww_mutex_lock(&lock->mutex, &ctx->ww_ctx);
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}
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if (!ret) {
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WARN_ON(!list_empty(&lock->head));
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list_add(&lock->head, &ctx->locked);
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} else if (ret == -EALREADY) {
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/* we already hold the lock.. this is fine. For atomic
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* we will need to be able to drm_modeset_lock() things
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* without having to keep track of what is already locked
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* or not.
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*/
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ret = 0;
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} else if (ret == -EDEADLK) {
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ctx->contended = lock;
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}
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return ret;
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}
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static int modeset_backoff(struct drm_modeset_acquire_ctx *ctx,
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bool interruptible)
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{
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struct drm_modeset_lock *contended = ctx->contended;
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ctx->contended = NULL;
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if (WARN_ON(!contended))
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return 0;
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drm_modeset_drop_locks(ctx);
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return modeset_lock(contended, ctx, interruptible, true);
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}
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/**
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* drm_modeset_backoff - deadlock avoidance backoff
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* @ctx: the acquire context
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*
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* If deadlock is detected (ie. drm_modeset_lock() returns -EDEADLK),
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* you must call this function to drop all currently held locks and
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* block until the contended lock becomes available.
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*/
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void drm_modeset_backoff(struct drm_modeset_acquire_ctx *ctx)
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{
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modeset_backoff(ctx, false);
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}
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EXPORT_SYMBOL(drm_modeset_backoff);
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/**
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* drm_modeset_backoff_interruptible - deadlock avoidance backoff
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* @ctx: the acquire context
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*
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* Interruptible version of drm_modeset_backoff()
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*/
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int drm_modeset_backoff_interruptible(struct drm_modeset_acquire_ctx *ctx)
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{
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return modeset_backoff(ctx, true);
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}
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EXPORT_SYMBOL(drm_modeset_backoff_interruptible);
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/**
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* drm_modeset_lock - take modeset lock
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* @lock: lock to take
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* @ctx: acquire ctx
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*
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* If ctx is not NULL, then its ww acquire context is used and the
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* lock will be tracked by the context and can be released by calling
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* drm_modeset_drop_locks(). If -EDEADLK is returned, this means a
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* deadlock scenario has been detected and it is an error to attempt
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* to take any more locks without first calling drm_modeset_backoff().
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*/
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int drm_modeset_lock(struct drm_modeset_lock *lock,
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struct drm_modeset_acquire_ctx *ctx)
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{
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if (ctx)
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return modeset_lock(lock, ctx, false, false);
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ww_mutex_lock(&lock->mutex, NULL);
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return 0;
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}
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EXPORT_SYMBOL(drm_modeset_lock);
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/**
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* drm_modeset_lock_interruptible - take modeset lock
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* @lock: lock to take
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* @ctx: acquire ctx
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*
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* Interruptible version of drm_modeset_lock()
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*/
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int drm_modeset_lock_interruptible(struct drm_modeset_lock *lock,
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struct drm_modeset_acquire_ctx *ctx)
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{
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if (ctx)
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return modeset_lock(lock, ctx, true, false);
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return ww_mutex_lock_interruptible(&lock->mutex, NULL);
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}
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EXPORT_SYMBOL(drm_modeset_lock_interruptible);
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/**
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* drm_modeset_unlock - drop modeset lock
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* @lock: lock to release
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*/
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void drm_modeset_unlock(struct drm_modeset_lock *lock)
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{
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list_del_init(&lock->head);
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ww_mutex_unlock(&lock->mutex);
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}
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EXPORT_SYMBOL(drm_modeset_unlock);
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/* Temporary.. until we have sufficiently fine grained locking, there
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* are a couple scenarios where it is convenient to grab all crtc locks.
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* It is planned to remove this:
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*/
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int drm_modeset_lock_all_crtcs(struct drm_device *dev,
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struct drm_modeset_acquire_ctx *ctx)
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{
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struct drm_mode_config *config = &dev->mode_config;
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struct drm_crtc *crtc;
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int ret = 0;
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list_for_each_entry(crtc, &config->crtc_list, head) {
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ret = drm_modeset_lock(&crtc->mutex, ctx);
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if (ret)
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return ret;
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}
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return 0;
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}
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EXPORT_SYMBOL(drm_modeset_lock_all_crtcs);
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