On Thu, Jul 27, 2017 at 04:03:53PM -0300, Gustavo Padovan wrote:
> From: Gustavo Padovan <gustavo.padovan@xxxxxxxxxxxxx>
>
> If userspace already dropped its own reference by closing the sw_sync
> fence fd we might end up in a deadlock where
> dma_fence_is_signaled_locked() will trigger the release of the fence a
> thus try to hold the lock to remove the fence from the list.
>
> We need to grab a reference to the fence before calling into this chain if
> we want to avoid this issue.
>
> Cc: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> Signed-off-by: Gustavo Padovan <gustavo.padovan@xxxxxxxxxxxxx>
Do we have a testcase for this?
-Daniel
> ---
> drivers/dma-buf/sw_sync.c | 7 ++++++-
> 1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/dma-buf/sw_sync.c b/drivers/dma-buf/sw_sync.c
> index af1bc84..8291434 100644
> --- a/drivers/dma-buf/sw_sync.c
> +++ b/drivers/dma-buf/sw_sync.c
> @@ -144,11 +144,16 @@ static void sync_timeline_signal(struct sync_timeline *obj, unsigned int inc)
> obj->value += inc;
>
> list_for_each_entry_safe(pt, next, &obj->pt_list, link) {
> - if (!dma_fence_is_signaled_locked(&pt->base))
> + dma_fence_get(&pt->base);
> + if (!dma_fence_is_signaled_locked(&pt->base)) {
> + dma_fence_put(&pt->base);
> break;
> + }
>
> list_del_init(&pt->link);
> rb_erase(&pt->node, &obj->pt_tree);
> +
> + dma_fence_put(&pt->base);
> }
>
> spin_unlock_irq(&obj->lock);
> --
> 2.9.4
>
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--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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