Re: [PATCH v2 2/3] dma-buf/sw_sync: Separate signal/timeline locks

[Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>]

Still Reviewed-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>

On Tue, Jul 14, 2020 at 11:24 PM Chris Wilson <chris@chris-wilson.co.uk> wrote:
>
> Since we decouple the sync_pt from the timeline tree upon release, in
> order to allow releasing the sync_pt from a signal callback we need to
> separate the sync_pt signaling lock from the timeline tree lock.
>
> v2: Mark up the unlocked read of the current timeline value.
> v3: Store a timeline pointer in the sync_pt as we cannot use the common
> fence->lock trick to find our parent anymore.
>
> Suggested-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
> ---
>  drivers/dma-buf/sw_sync.c    | 40 +++++++++++++++++++++---------------
>  drivers/dma-buf/sync_debug.c |  2 +-
>  drivers/dma-buf/sync_debug.h | 13 +++++++-----
>  3 files changed, 32 insertions(+), 23 deletions(-)
>
> diff --git a/drivers/dma-buf/sw_sync.c b/drivers/dma-buf/sw_sync.c
> index 807c82148062..17a5c1a3b7ce 100644
> --- a/drivers/dma-buf/sw_sync.c
> +++ b/drivers/dma-buf/sw_sync.c
> @@ -123,33 +123,39 @@ static const char *timeline_fence_get_driver_name(struct dma_fence *fence)
>
>  static const char *timeline_fence_get_timeline_name(struct dma_fence *fence)
>  {
> -       struct sync_timeline *parent = dma_fence_parent(fence);
> -
> -       return parent->name;
> +       return sync_timeline(fence)->name;
>  }
>
>  static void timeline_fence_release(struct dma_fence *fence)
>  {
>         struct sync_pt *pt = dma_fence_to_sync_pt(fence);
> -       struct sync_timeline *parent = dma_fence_parent(fence);
> -       unsigned long flags;
> +       struct sync_timeline *parent = pt->timeline;
>
> -       spin_lock_irqsave(fence->lock, flags);
>         if (!list_empty(&pt->link)) {
> -               list_del(&pt->link);
> -               rb_erase(&pt->node, &parent->pt_tree);
> +               unsigned long flags;
> +
> +               spin_lock_irqsave(&parent->lock, flags);
> +               if (!list_empty(&pt->link)) {
> +                       list_del(&pt->link);
> +                       rb_erase(&pt->node, &parent->pt_tree);
> +               }
> +               spin_unlock_irqrestore(&parent->lock, flags);
>         }
> -       spin_unlock_irqrestore(fence->lock, flags);
>
>         sync_timeline_put(parent);
>         dma_fence_free(fence);
>  }
>
> -static bool timeline_fence_signaled(struct dma_fence *fence)
> +static int timeline_value(struct dma_fence *fence)
>  {
> -       struct sync_timeline *parent = dma_fence_parent(fence);
> +       return READ_ONCE(sync_timeline(fence)->value);
> +}
>
> -       return !__dma_fence_is_later(fence->seqno, parent->value, fence->ops);
> +static bool timeline_fence_signaled(struct dma_fence *fence)
> +{
> +       return !__dma_fence_is_later(fence->seqno,
> +                                    timeline_value(fence),
> +                                    fence->ops);
>  }
>
>  static bool timeline_fence_enable_signaling(struct dma_fence *fence)
> @@ -166,9 +172,7 @@ static void timeline_fence_value_str(struct dma_fence *fence,
>  static void timeline_fence_timeline_value_str(struct dma_fence *fence,
>                                              char *str, int size)
>  {
> -       struct sync_timeline *parent = dma_fence_parent(fence);
> -
> -       snprintf(str, size, "%d", parent->value);
> +       snprintf(str, size, "%d", timeline_value(fence));
>  }
>
>  static const struct dma_fence_ops timeline_fence_ops = {
> @@ -252,12 +256,14 @@ static struct sync_pt *sync_pt_create(struct sync_timeline *obj,
>                 return NULL;
>
>         sync_timeline_get(obj);
> -       dma_fence_init(&pt->base, &timeline_fence_ops, &obj->lock,
> +       spin_lock_init(&pt->lock);
> +       dma_fence_init(&pt->base, &timeline_fence_ops, &pt->lock,
>                        obj->context, value);
>         INIT_LIST_HEAD(&pt->link);
> +       pt->timeline = obj;
>
>         spin_lock_irq(&obj->lock);
> -       if (!dma_fence_is_signaled_locked(&pt->base)) {
> +       if (!dma_fence_is_signaled(&pt->base)) {
>                 struct rb_node **p = &obj->pt_tree.rb_node;
>                 struct rb_node *parent = NULL;
>
> diff --git a/drivers/dma-buf/sync_debug.c b/drivers/dma-buf/sync_debug.c
> index 101394f16930..2188ee17e889 100644
> --- a/drivers/dma-buf/sync_debug.c
> +++ b/drivers/dma-buf/sync_debug.c
> @@ -65,7 +65,7 @@ static const char *sync_status_str(int status)
>  static void sync_print_fence(struct seq_file *s,
>                              struct dma_fence *fence, bool show)
>  {
> -       struct sync_timeline *parent = dma_fence_parent(fence);
> +       struct sync_timeline *parent = sync_timeline(fence);
>         int status;
>
>         status = dma_fence_get_status_locked(fence);
> diff --git a/drivers/dma-buf/sync_debug.h b/drivers/dma-buf/sync_debug.h
> index 6176e52ba2d7..56589dae2159 100644
> --- a/drivers/dma-buf/sync_debug.h
> +++ b/drivers/dma-buf/sync_debug.h
> @@ -45,23 +45,26 @@ struct sync_timeline {
>         struct list_head        sync_timeline_list;
>  };
>
> -static inline struct sync_timeline *dma_fence_parent(struct dma_fence *fence)
> -{
> -       return container_of(fence->lock, struct sync_timeline, lock);
> -}
> -
>  /**
>   * struct sync_pt - sync_pt object
>   * @base: base fence object
>   * @link: link on the sync timeline's list
>   * @node: node in the sync timeline's tree
> + * @lock: fence signaling lock
>   */
>  struct sync_pt {
>         struct dma_fence base;
> +       struct sync_timeline *timeline;
>         struct list_head link;
>         struct rb_node node;
> +       spinlock_t lock;
>  };
>
> +static inline struct sync_timeline *sync_timeline(struct dma_fence *fence)
> +{
> +       return container_of(fence, struct sync_pt, base)->timeline;
> +}
> +
>  extern const struct file_operations sw_sync_debugfs_fops;
>
>  void sync_timeline_debug_add(struct sync_timeline *obj);
> --
> 2.20.1
>
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