Re: [PATCH v6 2/6] dmaengine: virt-dma: Use lockdep to check locking requirements

[Peter Ujfalusi <peter.ujfalusi@ti.com>]

Hi Laurent,

On 08/07/2020 23.19, Laurent Pinchart wrote:
> A few virt-dma functions are documented as requiring the vc.lock to be
> held by the caller. Check this with lockdep.
> 
> The vchan_vdesc_fini() and vchan_find_desc() functions gain a lockdep

vchan_vdesc_fini() is used outside of held vc->lock via vchan_complete()
and the customized local re-implementation of it in ti/k3-udma.c

This patch did not adds the lockdep_assert_held() to the _fini.
The vchan_complete() can be issue only in  case when the descriptor is
set to DMA_CTRL_REUSE.

> check as well, because, even though they are not documented with this
> requirement (and not documented at all for the latter), they touch
> fields documented as protected by vc.lock. All callers have been
> manually inspected to verify they call the functions with the lock held.
> 
> Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> ---
>  drivers/dma/virt-dma.c |  2 ++
>  drivers/dma/virt-dma.h | 10 ++++++++++
>  2 files changed, 12 insertions(+)
> 
> diff --git a/drivers/dma/virt-dma.c b/drivers/dma/virt-dma.c
> index 23e33a85f033..1cb36ab3d9c1 100644
> --- a/drivers/dma/virt-dma.c
> +++ b/drivers/dma/virt-dma.c
> @@ -68,6 +68,8 @@ struct virt_dma_desc *vchan_find_desc(struct virt_dma_chan *vc,
>  {
>  	struct virt_dma_desc *vd;
>  
> +	lockdep_assert_held(&vc->lock);
> +
>  	list_for_each_entry(vd, &vc->desc_issued, node)
>  		if (vd->tx.cookie == cookie)
>  			return vd;
> diff --git a/drivers/dma/virt-dma.h b/drivers/dma/virt-dma.h
> index e9f5250fbe4d..59d9eabc8b67 100644
> --- a/drivers/dma/virt-dma.h
> +++ b/drivers/dma/virt-dma.h
> @@ -81,6 +81,8 @@ static inline struct dma_async_tx_descriptor *vchan_tx_prep(struct virt_dma_chan
>   */
>  static inline bool vchan_issue_pending(struct virt_dma_chan *vc)
>  {
> +	lockdep_assert_held(&vc->lock);
> +
>  	list_splice_tail_init(&vc->desc_submitted, &vc->desc_issued);
>  	return !list_empty(&vc->desc_issued);
>  }
> @@ -96,6 +98,8 @@ static inline void vchan_cookie_complete(struct virt_dma_desc *vd)
>  	struct virt_dma_chan *vc = to_virt_chan(vd->tx.chan);
>  	dma_cookie_t cookie;
>  
> +	lockdep_assert_held(&vc->lock);
> +
>  	cookie = vd->tx.cookie;
>  	dma_cookie_complete(&vd->tx);
>  	dev_vdbg(vc->chan.device->dev, "txd %p[%x]: marked complete\n",
> @@ -146,6 +150,8 @@ static inline void vchan_terminate_vdesc(struct virt_dma_desc *vd)
>  {
>  	struct virt_dma_chan *vc = to_virt_chan(vd->tx.chan);
>  
> +	lockdep_assert_held(&vc->lock);
> +
>  	list_add_tail(&vd->node, &vc->desc_terminated);
>  
>  	if (vc->cyclic == vd)
> @@ -160,6 +166,8 @@ static inline void vchan_terminate_vdesc(struct virt_dma_desc *vd)
>   */
>  static inline struct virt_dma_desc *vchan_next_desc(struct virt_dma_chan *vc)
>  {
> +	lockdep_assert_held(&vc->lock);
> +
>  	return list_first_entry_or_null(&vc->desc_issued,
>  					struct virt_dma_desc, node);
>  }
> @@ -177,6 +185,8 @@ static inline struct virt_dma_desc *vchan_next_desc(struct virt_dma_chan *vc)
>  static inline void vchan_get_all_descriptors(struct virt_dma_chan *vc,
>  	struct list_head *head)
>  {
> +	lockdep_assert_held(&vc->lock);
> +
>  	list_splice_tail_init(&vc->desc_allocated, head);
>  	list_splice_tail_init(&vc->desc_submitted, head);
>  	list_splice_tail_init(&vc->desc_issued, head);
> 

- Péter

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