OSCL-LXR linux-6.0.1/​drivers/​gpu/​drm/​i915/​i915_active.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

 /*
  * SPDX-License-Identifier: MIT
  *
  * Copyright © 2019 Intel Corporation
  */
 
 #include <linux/debugobjects.h>
 
 #include "gt/intel_context.h"
 #include "gt/intel_engine_heartbeat.h"
 #include "gt/intel_engine_pm.h"
 #include "gt/intel_ring.h"
 
 #include "i915_drv.h"
 #include "i915_active.h"
 
 /*
  * Active refs memory management
  *
  * To be more economical with memory, we reap all the i915_active trees as
  * they idle (when we know the active requests are inactive) and allocate the
  * nodes from a local slab cache to hopefully reduce the fragmentation.
  */
 static struct kmem_cache *slab_cache;
 
 struct active_node {
     struct rb_node node;
     struct i915_active_fence base;
     struct i915_active *ref;
     u64 timeline;
 };
 
 #define fetch_node(x) rb_entry(READ_ONCE(x), typeof(struct active_node), node)
 
 static inline struct active_node *
 node_from_active(struct i915_active_fence *active)
 {
     return container_of(active, struct active_node, base);
 }
 
 #define take_preallocated_barriers(x) llist_del_all(&(x)->preallocated_barriers)
 
 static inline bool is_barrier(const struct i915_active_fence *active)
 {
     return IS_ERR(rcu_access_pointer(active->fence));
 }
 
 static inline struct llist_node *barrier_to_ll(struct active_node *node)
 {
     GEM_BUG_ON(!is_barrier(&node->base));
     return (struct llist_node *)&node->base.cb.node;
 }
 
 static inline struct intel_engine_cs *
 __barrier_to_engine(struct active_node *node)
 {
     return (struct intel_engine_cs *)READ_ONCE(node->base.cb.node.prev);
 }
 
 static inline struct intel_engine_cs *
 barrier_to_engine(struct active_node *node)
 {
     GEM_BUG_ON(!is_barrier(&node->base));
     return __barrier_to_engine(node);
 }
 
 static inline struct active_node *barrier_from_ll(struct llist_node *x)
 {
     return container_of((struct list_head *)x,
                 struct active_node, base.cb.node);
 }
 
 #if IS_ENABLED(CONFIG_DRM_I915_DEBUG_GEM) && IS_ENABLED(CONFIG_DEBUG_OBJECTS)
 
 static void *active_debug_hint(void *addr)
 {
     struct i915_active *ref = addr;
 
     return (void *)ref->active ?: (void *)ref->retire ?: (void *)ref;
 }
 
 static const struct debug_obj_descr active_debug_desc = {
     .name = "i915_active",
     .debug_hint = active_debug_hint,
 };
 
 static void debug_active_init(struct i915_active *ref)
 {
     debug_object_init(ref, &active_debug_desc);
 }
 
 static void debug_active_activate(struct i915_active *ref)
 {
     lockdep_assert_held(&ref->tree_lock);
     if (!atomic_read(&ref->count)) /* before the first inc */
         debug_object_activate(ref, &active_debug_desc);
 }
 
 static void debug_active_deactivate(struct i915_active *ref)
 {
     lockdep_assert_held(&ref->tree_lock);
     if (!atomic_read(&ref->count)) /* after the last dec */
         debug_object_deactivate(ref, &active_debug_desc);
 }
 
 static void debug_active_fini(struct i915_active *ref)
 {
     debug_object_free(ref, &active_debug_desc);
 }
 
 static void debug_active_assert(struct i915_active *ref)
 {
     debug_object_assert_init(ref, &active_debug_desc);
 }
 
 #else
 
 static inline void debug_active_init(struct i915_active *ref) { }
 static inline void debug_active_activate(struct i915_active *ref) { }
 static inline void debug_active_deactivate(struct i915_active *ref) { }
 static inline void debug_active_fini(struct i915_active *ref) { }
 static inline void debug_active_assert(struct i915_active *ref) { }
 
 #endif
 
 static void
 __active_retire(struct i915_active *ref)
 {
     struct rb_root root = RB_ROOT;
     struct active_node *it, *n;
     unsigned long flags;
 
     GEM_BUG_ON(i915_active_is_idle(ref));
 
     /* return the unused nodes to our slabcache -- flushing the allocator */
     if (!atomic_dec_and_lock_irqsave(&ref->count, &ref->tree_lock, flags))
         return;
 
     GEM_BUG_ON(rcu_access_pointer(ref->excl.fence));
     debug_active_deactivate(ref);
 
     /* Even if we have not used the cache, we may still have a barrier */
     if (!ref->cache)
         ref->cache = fetch_node(ref->tree.rb_node);
 
     /* Keep the MRU cached node for reuse */
     if (ref->cache) {
         /* Discard all other nodes in the tree */
         rb_erase(&ref->cache->node, &ref->tree);
         root = ref->tree;
 
         /* Rebuild the tree with only the cached node */
         rb_link_node(&ref->cache->node, NULL, &ref->tree.rb_node);
         rb_insert_color(&ref->cache->node, &ref->tree);
         GEM_BUG_ON(ref->tree.rb_node != &ref->cache->node);
 
         /* Make the cached node available for reuse with any timeline */
         ref->cache->timeline = 0; /* needs cmpxchg(u64) */
     }
 
     spin_unlock_irqrestore(&ref->tree_lock, flags);
 
     /* After the final retire, the entire struct may be freed */
     if (ref->retire)
         ref->retire(ref);
 
     /* ... except if you wait on it, you must manage your own references! */
     wake_up_var(ref);
 
     /* Finally free the discarded timeline tree  */
     rbtree_postorder_for_each_entry_safe(it, n, &root, node) {
         GEM_BUG_ON(i915_active_fence_isset(&it->base));
         kmem_cache_free(slab_cache, it);
     }
 }
 
 static void
 active_work(struct work_struct *wrk)
 {
     struct i915_active *ref = container_of(wrk, typeof(*ref), work);
 
     GEM_BUG_ON(!atomic_read(&ref->count));
     if (atomic_add_unless(&ref->count, -1, 1))
         return;
 
     __active_retire(ref);
 }
 
 static void
 active_retire(struct i915_active *ref)
 {
     GEM_BUG_ON(!atomic_read(&ref->count));
     if (atomic_add_unless(&ref->count, -1, 1))
         return;
 
     if (ref->flags & I915_ACTIVE_RETIRE_SLEEPS) {
         queue_work(system_unbound_wq, &ref->work);
         return;
     }
 
     __active_retire(ref);
 }
 
 static inline struct dma_fence **
 __active_fence_slot(struct i915_active_fence *active)
 {
     return (struct dma_fence ** __force)&active->fence;
 }
 
 static inline bool
 active_fence_cb(struct dma_fence *fence, struct dma_fence_cb *cb)
 {
     struct i915_active_fence *active =
         container_of(cb, typeof(*active), cb);
 
     return cmpxchg(__active_fence_slot(active), fence, NULL) == fence;
 }
 
 static void
 node_retire(struct dma_fence *fence, struct dma_fence_cb *cb)
 {
     if (active_fence_cb(fence, cb))
         active_retire(container_of(cb, struct active_node, base.cb)->ref);
 }
 
 static void
 excl_retire(struct dma_fence *fence, struct dma_fence_cb *cb)
 {
     if (active_fence_cb(fence, cb))
         active_retire(container_of(cb, struct i915_active, excl.cb));
 }
 
 static struct active_node *__active_lookup(struct i915_active *ref, u64 idx)
 {
     struct active_node *it;
 
     GEM_BUG_ON(idx == 0); /* 0 is the unordered timeline, rsvd for cache */
 
     /*
      * We track the most recently used timeline to skip a rbtree search
      * for the common case, under typical loads we never need the rbtree
      * at all. We can reuse the last slot if it is empty, that is
      * after the previous activity has been retired, or if it matches the
      * current timeline.
      */
     it = READ_ONCE(ref->cache);
     if (it) {
         u64 cached = READ_ONCE(it->timeline);
 
         /* Once claimed, this slot will only belong to this idx */
         if (cached == idx)
             return it;
 
         /*
          * An unclaimed cache [.timeline=0] can only be claimed once.
          *
          * If the value is already non-zero, some other thread has
          * claimed the cache and we know that is does not match our
          * idx. If, and only if, the timeline is currently zero is it
          * worth competing to claim it atomically for ourselves (for
          * only the winner of that race will cmpxchg return the old
          * value of 0).
          */
         if (!cached && !cmpxchg64(&it->timeline, 0, idx))
             return it;
     }
 
     BUILD_BUG_ON(offsetof(typeof(*it), node));
 
     /* While active, the tree can only be built; not destroyed */
     GEM_BUG_ON(i915_active_is_idle(ref));
 
     it = fetch_node(ref->tree.rb_node);
     while (it) {
         if (it->timeline < idx) {
             it = fetch_node(it->node.rb_right);
         } else if (it->timeline > idx) {
             it = fetch_node(it->node.rb_left);
         } else {
             WRITE_ONCE(ref->cache, it);
             break;
         }
     }
 
     /* NB: If the tree rotated beneath us, we may miss our target. */
     return it;
 }
 
 static struct i915_active_fence *
 active_instance(struct i915_active *ref, u64 idx)
 {
     struct active_node *node;
     struct rb_node **p, *parent;
 
     node = __active_lookup(ref, idx);
     if (likely(node))
         return &node->base;
 
     spin_lock_irq(&ref->tree_lock);
     GEM_BUG_ON(i915_active_is_idle(ref));
 
     parent = NULL;
     p = &ref->tree.rb_node;
     while (*p) {
         parent = *p;
 
         node = rb_entry(parent, struct active_node, node);
         if (node->timeline == idx)
             goto out;
 
         if (node->timeline < idx)
             p = &parent->rb_right;
         else
             p = &parent->rb_left;
     }
 
     /*
      * XXX: We should preallocate this before i915_active_ref() is ever
      *  called, but we cannot call into fs_reclaim() anyway, so use GFP_ATOMIC.
      */
     node = kmem_cache_alloc(slab_cache, GFP_ATOMIC);
     if (!node)
         goto out;
 
     __i915_active_fence_init(&node->base, NULL, node_retire);
     node->ref = ref;
     node->timeline = idx;
 
     rb_link_node(&node->node, parent, p);
     rb_insert_color(&node->node, &ref->tree);
 
 out:
     WRITE_ONCE(ref->cache, node);
     spin_unlock_irq(&ref->tree_lock);
 
     return &node->base;
 }
 
 void __i915_active_init(struct i915_active *ref,
             int (*active)(struct i915_active *ref),
             void (*retire)(struct i915_active *ref),
             unsigned long flags,
             struct lock_class_key *mkey,
             struct lock_class_key *wkey)
 {
     debug_active_init(ref);
 
     ref->flags = flags;
     ref->active = active;
     ref->retire = retire;
 
     spin_lock_init(&ref->tree_lock);
     ref->tree = RB_ROOT;
     ref->cache = NULL;
 
     init_llist_head(&ref->preallocated_barriers);
     atomic_set(&ref->count, 0);
     __mutex_init(&ref->mutex, "i915_active", mkey);
     __i915_active_fence_init(&ref->excl, NULL, excl_retire);
     INIT_WORK(&ref->work, active_work);
 #if IS_ENABLED(CONFIG_LOCKDEP)
     lockdep_init_map(&ref->work.lockdep_map, "i915_active.work", wkey, 0);
 #endif
 }
 
 static bool ____active_del_barrier(struct i915_active *ref,
                    struct active_node *node,
                    struct intel_engine_cs *engine)
 
 {
     struct llist_node *head = NULL, *tail = NULL;
     struct llist_node *pos, *next;
 
     GEM_BUG_ON(node->timeline != engine->kernel_context->timeline->fence_context);
 
     /*
      * Rebuild the llist excluding our node. We may perform this
      * outside of the kernel_context timeline mutex and so someone
      * else may be manipulating the engine->barrier_tasks, in
      * which case either we or they will be upset :)
      *
      * A second __active_del_barrier() will report failure to claim
      * the active_node and the caller will just shrug and know not to
      * claim ownership of its node.
      *
      * A concurrent i915_request_add_active_barriers() will miss adding
      * any of the tasks, but we will try again on the next -- and since
      * we are actively using the barrier, we know that there will be
      * at least another opportunity when we idle.
      */
     llist_for_each_safe(pos, next, llist_del_all(&engine->barrier_tasks)) {
         if (node == barrier_from_ll(pos)) {
             node = NULL;
             continue;
         }
 
         pos->next = head;
         head = pos;
         if (!tail)
             tail = pos;
     }
     if (head)
         llist_add_batch(head, tail, &engine->barrier_tasks);
 
     return !node;
 }
 
 static bool
 __active_del_barrier(struct i915_active *ref, struct active_node *node)
 {
     return ____active_del_barrier(ref, node, barrier_to_engine(node));
 }
 
 static bool
 replace_barrier(struct i915_active *ref, struct i915_active_fence *active)
 {
     if (!is_barrier(active)) /* proto-node used by our idle barrier? */
         return false;
 
     /*
      * This request is on the kernel_context timeline, and so
      * we can use it to substitute for the pending idle-barrer
      * request that we want to emit on the kernel_context.
      */
     __active_del_barrier(ref, node_from_active(active));
     return true;
 }
 
 int i915_active_add_request(struct i915_active *ref, struct i915_request *rq)
 {
     struct dma_fence *fence = &rq->fence;
     struct i915_active_fence *active;
     int err;
 
     /* Prevent reaping in case we malloc/wait while building the tree */
     err = i915_active_acquire(ref);
     if (err)
         return err;
 
     active = active_instance(ref, i915_request_timeline(rq)->fence_context);
     if (!active) {
         err = -ENOMEM;
         goto out;
     }
 
     if (replace_barrier(ref, active)) {
         RCU_INIT_POINTER(active->fence, NULL);
         atomic_dec(&ref->count);
     }
     if (!__i915_active_fence_set(active, fence))
         __i915_active_acquire(ref);
 
 out:
     i915_active_release(ref);
     return err;
 }
 
 static struct dma_fence *
 __i915_active_set_fence(struct i915_active *ref,
             struct i915_active_fence *active,
             struct dma_fence *fence)
 {
     struct dma_fence *prev;
 
     if (replace_barrier(ref, active)) {
         RCU_INIT_POINTER(active->fence, fence);
         return NULL;
     }
 
     rcu_read_lock();
     prev = __i915_active_fence_set(active, fence);
     if (prev)
         prev = dma_fence_get_rcu(prev);
     else
         __i915_active_acquire(ref);
     rcu_read_unlock();
 
     return prev;
 }
 
 struct dma_fence *
 i915_active_set_exclusive(struct i915_active *ref, struct dma_fence *f)
 {
     /* We expect the caller to manage the exclusive timeline ordering */
     return __i915_active_set_fence(ref, &ref->excl, f);
 }
 
 bool i915_active_acquire_if_busy(struct i915_active *ref)
 {
     debug_active_assert(ref);
     return atomic_add_unless(&ref->count, 1, 0);
 }
 
 static void __i915_active_activate(struct i915_active *ref)
 {
     spin_lock_irq(&ref->tree_lock); /* __active_retire() */
     if (!atomic_fetch_inc(&ref->count))
         debug_active_activate(ref);
     spin_unlock_irq(&ref->tree_lock);
 }
 
 int i915_active_acquire(struct i915_active *ref)
 {
     int err;
 
     if (i915_active_acquire_if_busy(ref))
         return 0;
 
     if (!ref->active) {
         __i915_active_activate(ref);
         return 0;
     }
 
     err = mutex_lock_interruptible(&ref->mutex);
     if (err)
         return err;
 
     if (likely(!i915_active_acquire_if_busy(ref))) {
         err = ref->active(ref);
         if (!err)
             __i915_active_activate(ref);
     }
 
     mutex_unlock(&ref->mutex);
 
     return err;
 }
 
 int i915_active_acquire_for_context(struct i915_active *ref, u64 idx)
 {
     struct i915_active_fence *active;
     int err;
 
     err = i915_active_acquire(ref);
     if (err)
         return err;
 
     active = active_instance(ref, idx);
     if (!active) {
         i915_active_release(ref);
         return -ENOMEM;
     }
 
     return 0; /* return with active ref */
 }
 
 void i915_active_release(struct i915_active *ref)
 {
     debug_active_assert(ref);
     active_retire(ref);
 }
 
 static void enable_signaling(struct i915_active_fence *active)
 {
     struct dma_fence *fence;
 
     if (unlikely(is_barrier(active)))
         return;
 
     fence = i915_active_fence_get(active);
     if (!fence)
         return;
 
     dma_fence_enable_sw_signaling(fence);
     dma_fence_put(fence);
 }
 
 static int flush_barrier(struct active_node *it)
 {
     struct intel_engine_cs *engine;
 
     if (likely(!is_barrier(&it->base)))
         return 0;
 
     engine = __barrier_to_engine(it);
     smp_rmb(); /* serialise with add_active_barriers */
     if (!is_barrier(&it->base))
         return 0;
 
     return intel_engine_flush_barriers(engine);
 }
 
 static int flush_lazy_signals(struct i915_active *ref)
 {
     struct active_node *it, *n;
     int err = 0;
 
     enable_signaling(&ref->excl);
     rbtree_postorder_for_each_entry_safe(it, n, &ref->tree, node) {
         err = flush_barrier(it); /* unconnected idle barrier? */
         if (err)
             break;
 
         enable_signaling(&it->base);
     }
 
     return err;
 }
 
 int __i915_active_wait(struct i915_active *ref, int state)
 {
     might_sleep();
 
     /* Any fence added after the wait begins will not be auto-signaled */
     if (i915_active_acquire_if_busy(ref)) {
         int err;
 
         err = flush_lazy_signals(ref);
         i915_active_release(ref);
         if (err)
             return err;
 
         if (___wait_var_event(ref, i915_active_is_idle(ref),
                       state, 0, 0, schedule()))
             return -EINTR;
     }
 
     /*
      * After the wait is complete, the caller may free the active.
      * We have to flush any concurrent retirement before returning.
      */
     flush_work(&ref->work);
     return 0;
 }
 
 static int __await_active(struct i915_active_fence *active,
               int (*fn)(void *arg, struct dma_fence *fence),
               void *arg)
 {
     struct dma_fence *fence;
 
     if (is_barrier(active)) /* XXX flush the barrier? */
         return 0;
 
     fence = i915_active_fence_get(active);
     if (fence) {
         int err;
 
         err = fn(arg, fence);
         dma_fence_put(fence);
         if (err < 0)
             return err;
     }
 
     return 0;
 }
 
 struct wait_barrier {
     struct wait_queue_entry base;
     struct i915_active *ref;
 };
 
 static int
 barrier_wake(wait_queue_entry_t *wq, unsigned int mode, int flags, void *key)
 {
     struct wait_barrier *wb = container_of(wq, typeof(*wb), base);
 
     if (i915_active_is_idle(wb->ref)) {
         list_del(&wq->entry);
         i915_sw_fence_complete(wq->private);
         kfree(wq);
     }
 
     return 0;
 }
 
 static int __await_barrier(struct i915_active *ref, struct i915_sw_fence *fence)
 {
     struct wait_barrier *wb;
 
     wb = kmalloc(sizeof(*wb), GFP_KERNEL);
     if (unlikely(!wb))
         return -ENOMEM;
 
     GEM_BUG_ON(i915_active_is_idle(ref));
     if (!i915_sw_fence_await(fence)) {
         kfree(wb);
         return -EINVAL;
     }
 
     wb->base.flags = 0;
     wb->base.func = barrier_wake;
     wb->base.private = fence;
     wb->ref = ref;
 
     add_wait_queue(__var_waitqueue(ref), &wb->base);
     return 0;
 }
 
 static int await_active(struct i915_active *ref,
             unsigned int flags,
             int (*fn)(void *arg, struct dma_fence *fence),
             void *arg, struct i915_sw_fence *barrier)
 {
     int err = 0;
 
     if (!i915_active_acquire_if_busy(ref))
         return 0;
 
     if (flags & I915_ACTIVE_AWAIT_EXCL &&
         rcu_access_pointer(ref->excl.fence)) {
         err = __await_active(&ref->excl, fn, arg);
         if (err)
             goto out;
     }
 
     if (flags & I915_ACTIVE_AWAIT_ACTIVE) {
         struct active_node *it, *n;
 
         rbtree_postorder_for_each_entry_safe(it, n, &ref->tree, node) {
             err = __await_active(&it->base, fn, arg);
             if (err)
                 goto out;
         }
     }
 
     if (flags & I915_ACTIVE_AWAIT_BARRIER) {
         err = flush_lazy_signals(ref);
         if (err)
             goto out;
 
         err = __await_barrier(ref, barrier);
         if (err)
             goto out;
     }
 
 out:
     i915_active_release(ref);
     return err;
 }
 
 static int rq_await_fence(void *arg, struct dma_fence *fence)
 {
     return i915_request_await_dma_fence(arg, fence);
 }
 
 int i915_request_await_active(struct i915_request *rq,
                   struct i915_active *ref,
                   unsigned int flags)
 {
     return await_active(ref, flags, rq_await_fence, rq, &rq->submit);
 }
 
 static int sw_await_fence(void *arg, struct dma_fence *fence)
 {
     return i915_sw_fence_await_dma_fence(arg, fence, 0,
                          GFP_NOWAIT | __GFP_NOWARN);
 }
 
 int i915_sw_fence_await_active(struct i915_sw_fence *fence,
                    struct i915_active *ref,
                    unsigned int flags)
 {
     return await_active(ref, flags, sw_await_fence, fence, fence);
 }
 
 void i915_active_fini(struct i915_active *ref)
 {
     debug_active_fini(ref);
     GEM_BUG_ON(atomic_read(&ref->count));
     GEM_BUG_ON(work_pending(&ref->work));
     mutex_destroy(&ref->mutex);
 
     if (ref->cache)
         kmem_cache_free(slab_cache, ref->cache);
 }
 
 static inline bool is_idle_barrier(struct active_node *node, u64 idx)
 {
     return node->timeline == idx && !i915_active_fence_isset(&node->base);
 }
 
 static struct active_node *reuse_idle_barrier(struct i915_active *ref, u64 idx)
 {
     struct rb_node *prev, *p;
 
     if (RB_EMPTY_ROOT(&ref->tree))
         return NULL;
 
     GEM_BUG_ON(i915_active_is_idle(ref));
 
     /*
      * Try to reuse any existing barrier nodes already allocated for this
      * i915_active, due to overlapping active phases there is likely a
      * node kept alive (as we reuse before parking). We prefer to reuse
      * completely idle barriers (less hassle in manipulating the llists),
      * but otherwise any will do.
      */
     if (ref->cache && is_idle_barrier(ref->cache, idx)) {
         p = &ref->cache->node;
         goto match;
     }
 
     prev = NULL;
     p = ref->tree.rb_node;
     while (p) {
         struct active_node *node =
             rb_entry(p, struct active_node, node);
 
         if (is_idle_barrier(node, idx))
             goto match;
 
         prev = p;
         if (node->timeline < idx)
             p = READ_ONCE(p->rb_right);
         else
             p = READ_ONCE(p->rb_left);
     }
 
     /*
      * No quick match, but we did find the leftmost rb_node for the
      * kernel_context. Walk the rb_tree in-order to see if there were
      * any idle-barriers on this timeline that we missed, or just use
      * the first pending barrier.
      */
     for (p = prev; p; p = rb_next(p)) {
         struct active_node *node =
             rb_entry(p, struct active_node, node);
         struct intel_engine_cs *engine;
 
         if (node->timeline > idx)
             break;
 
         if (node->timeline < idx)
             continue;
 
         if (is_idle_barrier(node, idx))
             goto match;
 
         /*
          * The list of pending barriers is protected by the
          * kernel_context timeline, which notably we do not hold
          * here. i915_request_add_active_barriers() may consume
          * the barrier before we claim it, so we have to check
          * for success.
          */
         engine = __barrier_to_engine(node);
         smp_rmb(); /* serialise with add_active_barriers */
         if (is_barrier(&node->base) &&
             ____active_del_barrier(ref, node, engine))
             goto match;
     }
 
     return NULL;
 
 match:
     spin_lock_irq(&ref->tree_lock);
     rb_erase(p, &ref->tree); /* Hide from waits and sibling allocations */
     if (p == &ref->cache->node)
         WRITE_ONCE(ref->cache, NULL);
     spin_unlock_irq(&ref->tree_lock);
 
     return rb_entry(p, struct active_node, node);
 }
 
 int i915_active_acquire_preallocate_barrier(struct i915_active *ref,
                         struct intel_engine_cs *engine)
 {
     intel_engine_mask_t tmp, mask = engine->mask;
     struct llist_node *first = NULL, *last = NULL;
     struct intel_gt *gt = engine->gt;
 
     GEM_BUG_ON(i915_active_is_idle(ref));
 
     /* Wait until the previous preallocation is completed */
     while (!llist_empty(&ref->preallocated_barriers))
         cond_resched();
 
     /*
      * Preallocate a node for each physical engine supporting the target
      * engine (remember virtual engines have more than one sibling).
      * We can then use the preallocated nodes in
      * i915_active_acquire_barrier()
      */
     GEM_BUG_ON(!mask);
     for_each_engine_masked(engine, gt, mask, tmp) {
         u64 idx = engine->kernel_context->timeline->fence_context;
         struct llist_node *prev = first;
         struct active_node *node;
 
         rcu_read_lock();
         node = reuse_idle_barrier(ref, idx);
         rcu_read_unlock();
         if (!node) {
             node = kmem_cache_alloc(slab_cache, GFP_KERNEL);
             if (!node)
                 goto unwind;
 
             RCU_INIT_POINTER(node->base.fence, NULL);
             node->base.cb.func = node_retire;
             node->timeline = idx;
             node->ref = ref;
         }
 
         if (!i915_active_fence_isset(&node->base)) {
             /*
              * Mark this as being *our* unconnected proto-node.
              *
              * Since this node is not in any list, and we have
              * decoupled it from the rbtree, we can reuse the
              * request to indicate this is an idle-barrier node
              * and then we can use the rb_node and list pointers
              * for our tracking of the pending barrier.
              */
             RCU_INIT_POINTER(node->base.fence, ERR_PTR(-EAGAIN));
             node->base.cb.node.prev = (void *)engine;
             __i915_active_acquire(ref);
         }
         GEM_BUG_ON(rcu_access_pointer(node->base.fence) != ERR_PTR(-EAGAIN));
 
         GEM_BUG_ON(barrier_to_engine(node) != engine);
         first = barrier_to_ll(node);
         first->next = prev;
         if (!last)
             last = first;
         intel_engine_pm_get(engine);
     }
 
     GEM_BUG_ON(!llist_empty(&ref->preallocated_barriers));
     llist_add_batch(first, last, &ref->preallocated_barriers);
 
     return 0;
 
 unwind:
     while (first) {
         struct active_node *node = barrier_from_ll(first);
 
         first = first->next;
 
         atomic_dec(&ref->count);
         intel_engine_pm_put(barrier_to_engine(node));
 
         kmem_cache_free(slab_cache, node);
     }
     return -ENOMEM;
 }
 
 void i915_active_acquire_barrier(struct i915_active *ref)
 {
     struct llist_node *pos, *next;
     unsigned long flags;
 
     GEM_BUG_ON(i915_active_is_idle(ref));
 
     /*
      * Transfer the list of preallocated barriers into the
      * i915_active rbtree, but only as proto-nodes. They will be
      * populated by i915_request_add_active_barriers() to point to the
      * request that will eventually release them.
      */
     llist_for_each_safe(pos, next, take_preallocated_barriers(ref)) {
         struct active_node *node = barrier_from_ll(pos);
         struct intel_engine_cs *engine = barrier_to_engine(node);
         struct rb_node **p, *parent;
 
         spin_lock_irqsave_nested(&ref->tree_lock, flags,
                      SINGLE_DEPTH_NESTING);
         parent = NULL;
         p = &ref->tree.rb_node;
         while (*p) {
             struct active_node *it;
 
             parent = *p;
 
             it = rb_entry(parent, struct active_node, node);
             if (it->timeline < node->timeline)
                 p = &parent->rb_right;
             else
                 p = &parent->rb_left;
         }
         rb_link_node(&node->node, parent, p);
         rb_insert_color(&node->node, &ref->tree);
         spin_unlock_irqrestore(&ref->tree_lock, flags);
 
         GEM_BUG_ON(!intel_engine_pm_is_awake(engine));
         llist_add(barrier_to_ll(node), &engine->barrier_tasks);
         intel_engine_pm_put_delay(engine, 2);
     }
 }
 
 static struct dma_fence **ll_to_fence_slot(struct llist_node *node)
 {
     return __active_fence_slot(&barrier_from_ll(node)->base);
 }
 
 void i915_request_add_active_barriers(struct i915_request *rq)
 {
     struct intel_engine_cs *engine = rq->engine;
     struct llist_node *node, *next;
     unsigned long flags;
 
     GEM_BUG_ON(!intel_context_is_barrier(rq->context));
     GEM_BUG_ON(intel_engine_is_virtual(engine));
     GEM_BUG_ON(i915_request_timeline(rq) != engine->kernel_context->timeline);
 
     node = llist_del_all(&engine->barrier_tasks);
     if (!node)
         return;
     /*
      * Attach the list of proto-fences to the in-flight request such
      * that the parent i915_active will be released when this request
      * is retired.
      */
     spin_lock_irqsave(&rq->lock, flags);
     llist_for_each_safe(node, next, node) {
         /* serialise with reuse_idle_barrier */
         smp_store_mb(*ll_to_fence_slot(node), &rq->fence);
         list_add_tail((struct list_head *)node, &rq->fence.cb_list);
     }
     spin_unlock_irqrestore(&rq->lock, flags);
 }
 
 /*
  * __i915_active_fence_set: Update the last active fence along its timeline
  * @active: the active tracker
  * @fence: the new fence (under construction)
  *
  * Records the new @fence as the last active fence along its timeline in
  * this active tracker, moving the tracking callbacks from the previous
  * fence onto this one. Returns the previous fence (if not already completed),
  * which the caller must ensure is executed before the new fence. To ensure
  * that the order of fences within the timeline of the i915_active_fence is
  * understood, it should be locked by the caller.
  */
 struct dma_fence *
 __i915_active_fence_set(struct i915_active_fence *active,
             struct dma_fence *fence)
 {
     struct dma_fence *prev;
     unsigned long flags;
 
     if (fence == rcu_access_pointer(active->fence))
         return fence;
 
     GEM_BUG_ON(test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags));
 
     /*
      * Consider that we have two threads arriving (A and B), with
      * C already resident as the active->fence.
      *
      * A does the xchg first, and so it sees C or NULL depending
      * on the timing of the interrupt handler. If it is NULL, the
      * previous fence must have been signaled and we know that
      * we are first on the timeline. If it is still present,
      * we acquire the lock on that fence and serialise with the interrupt
      * handler, in the process removing it from any future interrupt
      * callback. A will then wait on C before executing (if present).
      *
      * As B is second, it sees A as the previous fence and so waits for
      * it to complete its transition and takes over the occupancy for
      * itself -- remembering that it needs to wait on A before executing.
      *
      * Note the strong ordering of the timeline also provides consistent
      * nesting rules for the fence->lock; the inner lock is always the
      * older lock.
      */
     spin_lock_irqsave(fence->lock, flags);
     prev = xchg(__active_fence_slot(active), fence);
     if (prev) {
         GEM_BUG_ON(prev == fence);
         spin_lock_nested(prev->lock, SINGLE_DEPTH_NESTING);
         __list_del_entry(&active->cb.node);
         spin_unlock(prev->lock); /* serialise with prev->cb_list */
     }
     list_add_tail(&active->cb.node, &fence->cb_list);
     spin_unlock_irqrestore(fence->lock, flags);
 
     return prev;
 }
 
 int i915_active_fence_set(struct i915_active_fence *active,
               struct i915_request *rq)
 {
     struct dma_fence *fence;
     int err = 0;
 
     /* Must maintain timeline ordering wrt previous active requests */
     rcu_read_lock();
     fence = __i915_active_fence_set(active, &rq->fence);
     if (fence) /* but the previous fence may not belong to that timeline! */
         fence = dma_fence_get_rcu(fence);
     rcu_read_unlock();
     if (fence) {
         err = i915_request_await_dma_fence(rq, fence);
         dma_fence_put(fence);
     }
 
     return err;
 }
 
 void i915_active_noop(struct dma_fence *fence, struct dma_fence_cb *cb)
 {
     active_fence_cb(fence, cb);
 }
 
 struct auto_active {
     struct i915_active base;
     struct kref ref;
 };
 
 struct i915_active *i915_active_get(struct i915_active *ref)
 {
     struct auto_active *aa = container_of(ref, typeof(*aa), base);
 
     kref_get(&aa->ref);
     return &aa->base;
 }
 
 static void auto_release(struct kref *ref)
 {
     struct auto_active *aa = container_of(ref, typeof(*aa), ref);
 
     i915_active_fini(&aa->base);
     kfree(aa);
 }
 
 void i915_active_put(struct i915_active *ref)
 {
     struct auto_active *aa = container_of(ref, typeof(*aa), base);
 
     kref_put(&aa->ref, auto_release);
 }
 
 static int auto_active(struct i915_active *ref)
 {
     i915_active_get(ref);
     return 0;
 }
 
 static void auto_retire(struct i915_active *ref)
 {
     i915_active_put(ref);
 }
 
 struct i915_active *i915_active_create(void)
 {
     struct auto_active *aa;
 
     aa = kmalloc(sizeof(*aa), GFP_KERNEL);
     if (!aa)
         return NULL;
 
     kref_init(&aa->ref);
     i915_active_init(&aa->base, auto_active, auto_retire, 0);
 
     return &aa->base;
 }
 
 #if IS_ENABLED(CONFIG_DRM_I915_SELFTEST)
 #include "selftests/i915_active.c"
 #endif
 
 void i915_active_module_exit(void)
 {
     kmem_cache_destroy(slab_cache);
 }
 
 int __init i915_active_module_init(void)
 {
     slab_cache = KMEM_CACHE(active_node, SLAB_HWCACHE_ALIGN);
     if (!slab_cache)
         return -ENOMEM;
 
     return 0;
 }

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