Re: [RESEND][PATCH 2/3] dma-buf: heaps: Add a WARN_ON should the vmap_cnt go negative

[Sumit Semwal]

Hi John, Suren,


On Wed, 20 Jan 2021 at 02:15, John Stultz <john.stultz@xxxxxxxxxx> wrote:
>
> We shouldn't vunmap more then we vmap, but if we do, make
> sure we complain loudly.

I was checking the general usage of vunmap in the kernel, and I
couldn't find many instances where we need to WARN_ON for the vunmap
count more than vmap count. Is there a specific need for this in the heaps?

Best,
Sumit.
>
> Cc: Sumit Semwal <sumit.semwal@xxxxxxxxxx>
> Cc: Liam Mark <lmark@xxxxxxxxxxxxxx>
> Cc: Laura Abbott <labbott@xxxxxxxxxx>
> Cc: Brian Starkey <Brian.Starkey@xxxxxxx>
> Cc: Hridya Valsaraju <hridya@xxxxxxxxxx>
> Cc: Suren Baghdasaryan <surenb@xxxxxxxxxx>
> Cc: Sandeep Patil <sspatil@xxxxxxxxxx>
> Cc: Daniel Mentz <danielmentz@xxxxxxxxxx>
> Cc: Chris Goldsworthy <cgoldswo@xxxxxxxxxxxxxx>
> Cc: Ørjan Eide <orjan.eide@xxxxxxx>
> Cc: Robin Murphy <robin.murphy@xxxxxxx>
> Cc: Ezequiel Garcia <ezequiel@xxxxxxxxxxxxx>
> Cc: Simon Ser <contact@xxxxxxxxxxx>
> Cc: James Jones <jajones@xxxxxxxxxx>
> Cc: linux-media@xxxxxxxxxxxxxxx
> Cc: dri-devel@xxxxxxxxxxxxxxxxxxxxx
> Suggested-by: Suren Baghdasaryan <surenb@xxxxxxxxxx>
> Signed-off-by: John Stultz <john.stultz@xxxxxxxxxx>
> ---
>  drivers/dma-buf/heaps/cma_heap.c    | 1 +
>  drivers/dma-buf/heaps/system_heap.c | 1 +
>  2 files changed, 2 insertions(+)
>
> diff --git a/drivers/dma-buf/heaps/cma_heap.c b/drivers/dma-buf/heaps/cma_heap.c
> index 364fc2f3e499..0c76cbc3fb11 100644
> --- a/drivers/dma-buf/heaps/cma_heap.c
> +++ b/drivers/dma-buf/heaps/cma_heap.c
> @@ -232,6 +232,7 @@ static void cma_heap_vunmap(struct dma_buf *dmabuf, struct dma_buf_map *map)
>         struct cma_heap_buffer *buffer = dmabuf->priv;
>
>         mutex_lock(&buffer->lock);
> +       WARN_ON(buffer->vmap_cnt == 0);
>         if (!--buffer->vmap_cnt) {
>                 vunmap(buffer->vaddr);
>                 buffer->vaddr = NULL;
> diff --git a/drivers/dma-buf/heaps/system_heap.c b/drivers/dma-buf/heaps/system_heap.c
> index 405351aad2a8..2321c91891f6 100644
> --- a/drivers/dma-buf/heaps/system_heap.c
> +++ b/drivers/dma-buf/heaps/system_heap.c
> @@ -273,6 +273,7 @@ static void system_heap_vunmap(struct dma_buf *dmabuf, struct dma_buf_map *map)
>         struct system_heap_buffer *buffer = dmabuf->priv;
>
>         mutex_lock(&buffer->lock);
> +       WARN_ON(buffer->vmap_cnt == 0);
>         if (!--buffer->vmap_cnt) {
>                 vunmap(buffer->vaddr);
>                 buffer->vaddr = NULL;
> --
> 2.17.1
>