Op 06-07-2020 om 08:19 schreef Chris Wilson:
> Sometimes we have to be very careful not to allocate underneath a mutex
> (or spinlock) and yet still want to track activity. Enter
> i915_active_acquire_for_context(). This raises the activity counter on
> i915_active prior to use and ensures that the fence-tree contains a slot
> for the context.
>
> Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> ---
> .../gpu/drm/i915/gem/i915_gem_execbuffer.c | 2 +-
> drivers/gpu/drm/i915/gt/intel_timeline.c | 4 +-
> drivers/gpu/drm/i915/i915_active.c | 113 +++++++++++++++---
> drivers/gpu/drm/i915/i915_active.h | 14 ++-
> 4 files changed, 113 insertions(+), 20 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
> index 1015c4fd9f3e..6d20be29ff3c 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
> @@ -1789,7 +1789,7 @@ __parser_mark_active(struct i915_vma *vma,
> {
> struct intel_gt_buffer_pool_node *node = vma->private;
>
> - return i915_active_ref(&node->active, tl, fence);
> + return i915_active_ref(&node->active, tl->fence_context, fence);
> }
>
> static int
> diff --git a/drivers/gpu/drm/i915/gt/intel_timeline.c b/drivers/gpu/drm/i915/gt/intel_timeline.c
> index 4546284fede1..e4a5326633b8 100644
> --- a/drivers/gpu/drm/i915/gt/intel_timeline.c
> +++ b/drivers/gpu/drm/i915/gt/intel_timeline.c
> @@ -479,7 +479,9 @@ __intel_timeline_get_seqno(struct intel_timeline *tl,
> * free it after the current request is retired, which ensures that
> * all writes into the cacheline from previous requests are complete.
> */
> - err = i915_active_ref(&tl->hwsp_cacheline->active, tl, &rq->fence);
> + err = i915_active_ref(&tl->hwsp_cacheline->active,
> + tl->fence_context,
> + &rq->fence);
> if (err)
> goto err_cacheline;
>
> diff --git a/drivers/gpu/drm/i915/i915_active.c b/drivers/gpu/drm/i915/i915_active.c
> index d960d0be5bd2..3f595446fd44 100644
> --- a/drivers/gpu/drm/i915/i915_active.c
> +++ b/drivers/gpu/drm/i915/i915_active.c
> @@ -217,11 +217,10 @@ excl_retire(struct dma_fence *fence, struct dma_fence_cb *cb)
> }
>
> static struct i915_active_fence *
> -active_instance(struct i915_active *ref, struct intel_timeline *tl)
> +active_instance(struct i915_active *ref, u64 idx)
> {
> struct active_node *node, *prealloc;
> struct rb_node **p, *parent;
> - u64 idx = tl->fence_context;
>
> /*
> * We track the most recently used timeline to skip a rbtree search
> @@ -353,21 +352,17 @@ __active_del_barrier(struct i915_active *ref, struct active_node *node)
> return ____active_del_barrier(ref, node, barrier_to_engine(node));
> }
>
> -int i915_active_ref(struct i915_active *ref,
> - struct intel_timeline *tl,
> - struct dma_fence *fence)
> +int i915_active_ref(struct i915_active *ref, u64 idx, struct dma_fence *fence)
> {
> struct i915_active_fence *active;
> int err;
>
> - lockdep_assert_held(&tl->mutex);
> -
> /* Prevent reaping in case we malloc/wait while building the tree */
> err = i915_active_acquire(ref);
> if (err)
> return err;
>
> - active = active_instance(ref, tl);
> + active = active_instance(ref, idx);
> if (!active) {
> err = -ENOMEM;
> goto out;
> @@ -384,32 +379,104 @@ int i915_active_ref(struct i915_active *ref,
> atomic_dec(&ref->count);
> }
> if (!__i915_active_fence_set(active, fence))
> - atomic_inc(&ref->count);
> + __i915_active_acquire(ref);
>
> out:
> i915_active_release(ref);
> return err;
> }
>
> -struct dma_fence *
> -i915_active_set_exclusive(struct i915_active *ref, struct dma_fence *f)
> +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;
>
> /* We expect the caller to manage the exclusive timeline ordering */
> GEM_BUG_ON(i915_active_is_idle(ref));
>
> + if (is_barrier(active)) { /* proto-node used by our idle barrier */
> + /*
> + * 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));
> + RCU_INIT_POINTER(active->fence, NULL);
> + atomic_dec(&ref->count);
> + }
> +
> rcu_read_lock();
> - prev = __i915_active_fence_set(&ref->excl, f);
> + prev = __i915_active_fence_set(active, fence);
> if (prev)
> prev = dma_fence_get_rcu(prev);
> else
> - atomic_inc(&ref->count);
> + __i915_active_acquire(ref);
> rcu_read_unlock();
>
> return prev;
> }
>
> +static struct i915_active_fence *
> +__active_lookup(struct i915_active *ref, u64 idx)
> +{
> + struct active_node *node;
> + struct rb_node *p;
> +
> + /* Like active_instance() but with no malloc */
> +
> + node = READ_ONCE(ref->cache);
> + if (node && node->timeline == idx)
> + return &node->base;
> +
> + spin_lock_irq(&ref->tree_lock);
> + GEM_BUG_ON(i915_active_is_idle(ref));
> +
> + p = ref->tree.rb_node;
> + while (p) {
> + node = rb_entry(p, struct active_node, node);
> + if (node->timeline == idx) {
> + ref->cache = node;
> + spin_unlock_irq(&ref->tree_lock);
> + return &node->base;
> + }
> +
> + if (node->timeline < idx)
> + p = p->rb_right;
> + else
> + p = p->rb_left;
> + }
> +
> + spin_unlock_irq(&ref->tree_lock);
> +
> + return NULL;
> +}
> +
> +struct dma_fence *
> +__i915_active_ref(struct i915_active *ref, u64 idx, struct dma_fence *fence)
> +{
> + struct dma_fence *prev = ERR_PTR(-ENOENT);
> + struct i915_active_fence *active;
> +
> + if (!i915_active_acquire_if_busy(ref))
> + return ERR_PTR(-EINVAL);
> +
> + active = __active_lookup(ref, idx);
> + if (active)
> + prev = __i915_active_set_fence(ref, active, fence);
> +
> + i915_active_release(ref);
> + 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);
> @@ -443,6 +510,24 @@ int i915_active_acquire(struct i915_active *ref)
> 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);
> @@ -804,7 +889,7 @@ int i915_active_acquire_preallocate_barrier(struct i915_active *ref,
> */
> RCU_INIT_POINTER(node->base.fence, ERR_PTR(-EAGAIN));
> node->base.cb.node.prev = (void *)engine;
> - atomic_inc(&ref->count);
> + __i915_active_acquire(ref);
> }
> GEM_BUG_ON(rcu_access_pointer(node->base.fence) != ERR_PTR(-EAGAIN));
>
> diff --git a/drivers/gpu/drm/i915/i915_active.h b/drivers/gpu/drm/i915/i915_active.h
> index cf4058150966..2e0bcb3289ec 100644
> --- a/drivers/gpu/drm/i915/i915_active.h
> +++ b/drivers/gpu/drm/i915/i915_active.h
> @@ -163,14 +163,18 @@ void __i915_active_init(struct i915_active *ref,
> __i915_active_init(ref, active, retire, &__mkey, &__wkey); \
> } while (0)
>
> -int i915_active_ref(struct i915_active *ref,
> - struct intel_timeline *tl,
> - struct dma_fence *fence);
> +struct dma_fence *
> +__i915_active_ref(struct i915_active *ref, u64 idx, struct dma_fence *fence);
> +int i915_active_ref(struct i915_active *ref, u64 idx, struct dma_fence *fence);
>
> static inline int
> i915_active_add_request(struct i915_active *ref, struct i915_request *rq)
> {
> - return i915_active_ref(ref, i915_request_timeline(rq), &rq->fence);
> + struct intel_timeline *tl = i915_request_timeline(rq);
> +
> + lockdep_assert_held(&tl->mutex);
> +
> + return i915_active_ref(ref, tl->fence_context, &rq->fence);
> }
>
> struct dma_fence *
> @@ -198,7 +202,9 @@ int i915_request_await_active(struct i915_request *rq,
> #define I915_ACTIVE_AWAIT_BARRIER BIT(2)
>
> int i915_active_acquire(struct i915_active *ref);
> +int i915_active_acquire_for_context(struct i915_active *ref, u64 idx);
> bool i915_active_acquire_if_busy(struct i915_active *ref);
> +
> void i915_active_release(struct i915_active *ref);
>
> static inline void __i915_active_acquire(struct i915_active *ref)
Somewhere this is hiding a locking inversion in the later part of this series.
tl->mutex needs to be an inner lock of ww objects, see my patch series.
Since this is not the case, you're somehow hiding a locking inversion.
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