Hi Jacopo,
Thank you for the patch.
On Thu, May 29, 2025 at 06:36:30PM +0200, Jacopo Mondi wrote:
> In order to detect invalid usage pattern such as double list_put()
> calls, add a usage counter to each display list. Increment it whenever
> a list is get() and decrement it when the list is put(). Warn if the
> usage counter goes below 0.
>
> Signed-off-by: Jacopo Mondi <jacopo.mondi+renesas@xxxxxxxxxxxxxxxx>
> ---
> drivers/media/platform/renesas/vsp1/vsp1_dl.c | 7 +++++++
> 1 file changed, 7 insertions(+)
>
> diff --git a/drivers/media/platform/renesas/vsp1/vsp1_dl.c b/drivers/media/platform/renesas/vsp1/vsp1_dl.c
> index bb8228b19824..8a3c0274a163 100644
> --- a/drivers/media/platform/renesas/vsp1/vsp1_dl.c
> +++ b/drivers/media/platform/renesas/vsp1/vsp1_dl.c
> @@ -179,6 +179,7 @@ struct vsp1_dl_cmd_pool {
> * @has_chain: if true, indicates that there's a partition chain
> * @chain: entry in the display list partition chain
> * @flags: display list flags, a combination of VSP1_DL_FRAME_END_*
> + * @usage: usage counter to detect double list free
> */
> struct vsp1_dl_list {
> struct list_head list;
> @@ -198,6 +199,7 @@ struct vsp1_dl_list {
> struct list_head chain;
>
> unsigned int flags;
> + int usage;
If you have no objection, I'd like to include "count" in the name. This
could be usage_count, ref_count or refcount.
> };
>
> /**
> @@ -617,6 +619,7 @@ struct vsp1_dl_list *vsp1_dl_list_get(struct vsp1_dl_manager *dlm)
> * display list can assert list_empty() if it is not in a chain.
> */
> INIT_LIST_HEAD(&dl->chain);
> + dl->usage++;
The usage count will never go above 1, as there's not real reference
counting for display lists. Better than including "count" in the field
name, we could replace
int usage;
with
bool allocated;
(right after has_chain to avoid increasing the structure size).
> }
>
> spin_unlock_irqrestore(&dlm->lock, flags);
> @@ -657,6 +660,10 @@ static void __vsp1_dl_list_put(struct vsp1_dl_list *dl)
> */
> dl->body0->num_entries = 0;
>
> + /* decrement usage count to detect invalid usage pattern. */
s/decrement/Decrement/
> + if (WARN_ON_ONCE(--dl->usage < 0))
> + dl->usage = 0;
> +
> list_add_tail(&dl->list, &dl->dlm->free);
> }
>
--
Regards,
Laurent Pinchart
