Re: [PATCH] dma-buf: revert "use inline lock for the dma-fence-chain"

[Matthew Brost <matthew.brost@intel.com>]

On Mon, Feb 23, 2026 at 12:18:38PM -0800, Matthew Brost wrote:
> On Mon, Feb 23, 2026 at 08:57:05PM +0100, Christian König wrote:
> > This reverts commit a408c0ca0c411ca1ead995bdae3112a806c87556.
> > 
> > This causes a lockdep splat. Not really the right fix, but changing this
> > is more work than expected.
> > 

Ping - this is blocking our CI so if we can figure out the best way to
move forward soon, it is would be helpful.

Mstt 

> 
> I think dma-fence-arrays will have the same issue.
> 
> Can’t we just assign a lockdep key for chains and arrays?
> 
> Typing as fast as I could, I came up with this, and it seems to work:
> 
> diff --git a/drivers/dma-buf/dma-fence-array.c b/drivers/dma-buf/dma-fence-array.c
> index cd970eceaefb..d5cce24dca5b 100644
> --- a/drivers/dma-buf/dma-fence-array.c
> +++ b/drivers/dma-buf/dma-fence-array.c
> @@ -200,6 +200,10 @@ void dma_fence_array_init(struct dma_fence_array *array,
>                           u64 context, unsigned seqno,
>                           bool signal_on_any)
>  {
> +#if IS_ENABLED(CONFIG_PROVE_LOCKING)
> +       static struct lock_class_key dma_fence_array_lock_key;
> +#endif
> +
>         WARN_ON(!num_fences || !fences);
> 
>         array->num_fences = num_fences;
> @@ -208,6 +212,10 @@ void dma_fence_array_init(struct dma_fence_array *array,
>                        seqno);
>         init_irq_work(&array->work, irq_dma_fence_array_work);
> 
> +#if IS_ENABLED(CONFIG_PROVE_LOCKING)
> +       lockdep_set_class(&array->base.inline_lock, &dma_fence_array_lock_key);
> +#endif
> +
>         atomic_set(&array->num_pending, signal_on_any ? 1 : num_fences);
>         array->fences = fences;
> 
> diff --git a/drivers/dma-buf/dma-fence-chain.c b/drivers/dma-buf/dma-fence-chain.c
> index a707792b6025..aa144b8c3534 100644
> --- a/drivers/dma-buf/dma-fence-chain.c
> +++ b/drivers/dma-buf/dma-fence-chain.c
> @@ -242,6 +242,9 @@ void dma_fence_chain_init(struct dma_fence_chain *chain,
>                           struct dma_fence *fence,
>                           uint64_t seqno)
>  {
> +#if IS_ENABLED(CONFIG_PROVE_LOCKING)
> +       static struct lock_class_key dma_fence_chain_lock_key;
> +#endif
>         struct dma_fence_chain *prev_chain = to_dma_fence_chain(prev);
>         uint64_t context;
> 
> @@ -263,6 +266,10 @@ void dma_fence_chain_init(struct dma_fence_chain *chain,
>         dma_fence_init64(&chain->base, &dma_fence_chain_ops, NULL,
>                          context, seqno);
> 
> +#if IS_ENABLED(CONFIG_PROVE_LOCKING)
> +       lockdep_set_class(&chain->base.inline_lock, &dma_fence_chain_lock_key);
> +#endif
> +
>         /*
>          * Chaining dma_fence_chain container together is only allowed through
>          * the prev fence and not through the contained fence.
> 
> Matt
> 
> > Signed-off-by: Christian König <christian.koenig@amd.com>
> > ---
> >  drivers/dma-buf/dma-fence-chain.c | 3 ++-
> >  include/linux/dma-fence-chain.h   | 1 +
> >  2 files changed, 3 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/dma-buf/dma-fence-chain.c b/drivers/dma-buf/dma-fence-chain.c
> > index a707792b6025..a8a90acf4f34 100644
> > --- a/drivers/dma-buf/dma-fence-chain.c
> > +++ b/drivers/dma-buf/dma-fence-chain.c
> > @@ -245,6 +245,7 @@ void dma_fence_chain_init(struct dma_fence_chain *chain,
> >  	struct dma_fence_chain *prev_chain = to_dma_fence_chain(prev);
> >  	uint64_t context;
> >  
> > +	spin_lock_init(&chain->lock);
> >  	rcu_assign_pointer(chain->prev, prev);
> >  	chain->fence = fence;
> >  	chain->prev_seqno = 0;
> > @@ -260,7 +261,7 @@ void dma_fence_chain_init(struct dma_fence_chain *chain,
> >  			seqno = max(prev->seqno, seqno);
> >  	}
> >  
> > -	dma_fence_init64(&chain->base, &dma_fence_chain_ops, NULL,
> > +	dma_fence_init64(&chain->base, &dma_fence_chain_ops, &chain->lock,
> >  			 context, seqno);
> >  
> >  	/*
> > diff --git a/include/linux/dma-fence-chain.h b/include/linux/dma-fence-chain.h
> > index df3beadf1515..5cd3ba53b4a1 100644
> > --- a/include/linux/dma-fence-chain.h
> > +++ b/include/linux/dma-fence-chain.h
> > @@ -46,6 +46,7 @@ struct dma_fence_chain {
> >  		 */
> >  		struct irq_work work;
> >  	};
> > +	spinlock_t lock;
> >  };
> >  
> >  
> > -- 
> > 2.43.0
> >