Quoting Christian König (2017-08-13 14:04:29)
> Am 11.08.2017 um 19:01 schrieb Chris Wilson:
> > This is an illegal scenario, to free the fence whilst there are pending
> > callbacks. Currently, we emit a WARN and then cast aside the callbacks
> > leaving them dangling. Alternatively, we could set an error on the fence
> > and then signal fence so that any dependency chains from the fence can
> > be tidied up, and if they care they can check for the error.
> >
> > The question is whether or not the cure is worse than the disease
> > (premature fence signaling is never pretty).
> >
> > Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
>
> Not sure if -EDEADLK is the best error code, but in general the approach
> sounds like the least evil to me.
>
> Patch is Reviewed-by: Christian König <christian.koenig@xxxxxxx>.
Since the spectre of an early dma_fence_release() has shown itself
recently, I thought I'd ping this patch for inclusion along with the new
comment.
-Chris
> > ---
> > drivers/dma-buf/dma-fence.c | 14 +++++++++++++-
> > 1 file changed, 13 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/dma-buf/dma-fence.c b/drivers/dma-buf/dma-fence.c
> > index 9a302799040e..ed311edbeefa 100644
> > --- a/drivers/dma-buf/dma-fence.c
> > +++ b/drivers/dma-buf/dma-fence.c
> > @@ -172,7 +172,19 @@ void dma_fence_release(struct kref *kref)
> >
> > trace_dma_fence_destroy(fence);
> >
> > - WARN_ON(!list_empty(&fence->cb_list));
> > + if (WARN_ON(!list_empty(&fence->cb_list))) {
> > + unsigned long flags;
> > +
> > + /*
> > + * This should never happen, but if it does make sure that we
> > + * don't leave chains dangling. We set the error flag first
> > + * so that the callbacks know this signal is due to an error.
> > + */
> > + spin_lock_irqsave(fence->lock, flags);
> > + fence->error = -EDEADLK;
> > + dma_fence_signal_locked(fence);
> > + spin_unlock_irqrestore(fence->lock, flags);
> > + }
> >
> > if (fence->ops->release)
> > fence->ops->release(fence);
>
>
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