Op 10-07-2020 om 14:24 schreef Tvrtko Ursulin:
>
> On 09/07/2020 15:36, Maarten Lankhorst wrote:
>> 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.
>
> Which locks you think and from where? I want to make sure I am not missing something while reading the series..
>
> There used to be (still is in upstream) a possible deadlock with async get pages if batch buffer was an userptr object, but this series solves that by pre-allocating page directories in the reservation phase. That's not a plain locking inversion, but maybe that's what you had in mind?
>
> Does it take tl->mutex undeer dma_fence_wait? I can't see that it does.
>
> Can't think of any other options at the moment.
>
> Regards,
>
> Tvrtko
Ah never mind, context pinning/throttling is not reworked yet here.
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