/* * 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 <linux/export.h> #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) { unsigned long entries[8]; unsigned int n; n = stack_trace_save(entries, ARRAY_SIZE(entries), 1); return stack_depot_save(entries, n, GFP_NOWAIT | __GFP_NOWARN); } static void __drm_stack_depot_print(depot_stack_handle_t stack_depot) { struct drm_printer p = drm_dbg_printer(NULL, DRM_UT_KMS, "drm_modeset_lock"); unsigned long *entries; unsigned int nr_entries; char *buf; buf = kmalloc(PAGE_SIZE, GFP_NOWAIT | __GFP_NOWARN); if (!buf) return; nr_entries = stack_depot_fetch(stack_depot, &entries); stack_trace_snprint(buf, PAGE_SIZE, entries, nr_entries, 2); drm_printf(&p, "attempting to lock a contended lock without backoff:\n%s", buf); kfree(buf); } static void __drm_stack_depot_init(void) { stack_depot_init(); } #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) { struct drm_mode_config *config = &dev->mode_config; struct drm_modeset_acquire_ctx *ctx; int ret; ctx = kzalloc_obj(*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) { if (WARN_ON(ctx->contended)) __drm_stack_depot_print(ctx->stack_depot); 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; if (WARN_ON(ctx->contended)) __drm_stack_depot_print(ctx->stack_depot); if (ctx->trylock_only) { lockdep_assert_held(&ctx->ww_ctx); if (!ww_mutex_trylock(&lock->mutex, NULL)) 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; ctx->stack_depot = __drm_stack_depot_save(); } 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; ctx->stack_depot = 0; 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); __drm_stack_depot_init(); } 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);
