OSCL-LXR linux-6.0.1/​drivers/​gpu/​drm/​drm_modeset_lock.c	Source navigation Diff markup Identifier search General search
	Version: linux-6.0.1 spark-3.0.0 hadoop-3.2.0-src hadoop-3.3.0-src spark-2.4.7 linux-4.15.13 hadoop-2.7.4-src Revert   Change

 /*
  * 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>
 #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_debug_printer("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(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)
 {
     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);

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