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From:   Sumit Semwal <sumit.semwal@linaro.org>
Date:   Fri, 22 Jan 2021 13:26:29 +0530
Message-ID: <CAO_48GEYGzY8cZybwrXgfODhuoAJqi4AvwbZbWd+PiYjMqKYpw@mail.gmail.com>
Subject: Re: [RESEND][PATCH 2/3] dma-buf: heaps: Add a WARN_ON should the
 vmap_cnt go negative
To:     John Stultz <john.stultz@linaro.org>
Cc:     lkml <linux-kernel@vger.kernel.org>,
        Liam Mark <lmark@codeaurora.org>,
        Laura Abbott <labbott@kernel.org>,
        Brian Starkey <Brian.Starkey@arm.com>,
        Hridya Valsaraju <hridya@google.com>,
        Suren Baghdasaryan <surenb@google.com>,
        Sandeep Patil <sspatil@google.com>,
        Daniel Mentz <danielmentz@google.com>,
        Chris Goldsworthy <cgoldswo@codeaurora.org>,
        =?UTF-8?Q?=C3=98rjan_Eide?= <orjan.eide@arm.com>,
        Robin Murphy <robin.murphy@arm.com>,
        Ezequiel Garcia <ezequiel@collabora.com>,
        Simon Ser <contact@emersion.fr>,
        James Jones <jajones@nvidia.com>,
        "open list:DMA BUFFER SHARING FRAMEWORK" 
        <linux-media@vger.kernel.org>,
        DRI mailing list <dri-devel@lists.freedesktop.org>
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Hi John, Suren,


On Wed, 20 Jan 2021 at 02:15, John Stultz <john.stultz@linaro.org> 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@linaro.org>
> Cc: Liam Mark <lmark@codeaurora.org>
> Cc: Laura Abbott <labbott@kernel.org>
> Cc: Brian Starkey <Brian.Starkey@arm.com>
> Cc: Hridya Valsaraju <hridya@google.com>
> Cc: Suren Baghdasaryan <surenb@google.com>
> Cc: Sandeep Patil <sspatil@google.com>
> Cc: Daniel Mentz <danielmentz@google.com>
> Cc: Chris Goldsworthy <cgoldswo@codeaurora.org>
> Cc: =C3=98rjan Eide <orjan.eide@arm.com>
> Cc: Robin Murphy <robin.murphy@arm.com>
> Cc: Ezequiel Garcia <ezequiel@collabora.com>
> Cc: Simon Ser <contact@emersion.fr>
> Cc: James Jones <jajones@nvidia.com>
> Cc: linux-media@vger.kernel.org
> Cc: dri-devel@lists.freedesktop.org
> Suggested-by: Suren Baghdasaryan <surenb@google.com>
> Signed-off-by: John Stultz <john.stultz@linaro.org>
> ---
>  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, s=
truct dma_buf_map *map)
>         struct cma_heap_buffer *buffer =3D dmabuf->priv;
>
>         mutex_lock(&buffer->lock);
> +       WARN_ON(buffer->vmap_cnt =3D=3D 0);
>         if (!--buffer->vmap_cnt) {
>                 vunmap(buffer->vaddr);
>                 buffer->vaddr =3D 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 =3D dmabuf->priv;
>
>         mutex_lock(&buffer->lock);
> +       WARN_ON(buffer->vmap_cnt =3D=3D 0);
>         if (!--buffer->vmap_cnt) {
>                 vunmap(buffer->vaddr);
>                 buffer->vaddr =3D NULL;
> --
> 2.17.1
>