[PATCH 2/2] dma-buf/sw_sync: force signal all unsignaled fences on dying timeline

[Chris Wilson]

Quoting Gustavo Padovan (2017-09-05 00:06:04)
> From: Dominik Behr <dbehr at chromium.org>
> 
> To avoid hanging userspace components that might have been waiting on the
> active fences of the destroyed timeline we need to signal with error all
> remaining fences on such timeline.
> 
> This restore the default behaviour of the Android sw_sync framework, which
> Android still relies on. It was broken on the dma fence conversion a few
> years ago and never fixed.
> 
> Signed-off-by: Dominik Behr <dbehr at chromium.org>
> Signed-off-by: Gustavo Padovan <gustavo.padovan at collabora.com>
> ---
>  drivers/dma-buf/sw_sync.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/drivers/dma-buf/sw_sync.c b/drivers/dma-buf/sw_sync.c
> index 38cc7389a6c1..a85198c75a1b 100644
> --- a/drivers/dma-buf/sw_sync.c
> +++ b/drivers/dma-buf/sw_sync.c
> @@ -321,9 +321,21 @@ static int sw_sync_debugfs_open(struct inode *inode, struct file *file)
>  static int sw_sync_debugfs_release(struct inode *inode, struct file *file)
>  {
>         struct sync_timeline *obj = file->private_data;
> +       struct sync_pt *pt, *next;
>  
>         smp_wmb();
>  
> +       spin_lock_irq(&obj->lock);
> +
> +       list_for_each_entry_safe(pt, next, &obj->pt_list, link) {
> +               dma_fence_set_error(&pt->base, -ENOENT);
> +               dma_fence_signal_locked(&pt->base);
> +               list_del_init(&pt->link);
> +               rb_erase(&pt->node, &obj->pt_tree);

Since the timeline is dead, we don't need to worry about trimming the
completed signals from the timeline. No need for the
list_del/rb_erase here, especially considering the trickiness required
to avoid the potential deadlock which is missing here.
-Chris