Re: [PATCH] staging: ion: WARN when the handle kmap_cnt is going to wrap around

[Colin Cross]

On Thu, May 22, 2014 at 5:51 PM, Mitchel Humpherys
<mitchelh@xxxxxxxxxxxxxx> wrote:
> There are certain client bugs (double unmap, for example) that can cause
> the handle->kmap_cnt (an unsigned int) to wrap around from zero. This
> causes problems when the handle is destroyed because we have:
>
>         while (handle->kmap_cnt)
>                 ion_handle_kmap_put(handle);
>
> which takes a long time to complete when kmap_cnt starts at ~0 and can
> result in a watchdog timeout.
>
> WARN and bail when kmap_cnt is about to wrap around from zero.
>
> Signed-off-by: Mitchel Humpherys <mitchelh@xxxxxxxxxxxxxx>
> ---
>  drivers/staging/android/ion/ion.c | 4 ++++
>  1 file changed, 4 insertions(+)
>
> diff --git a/drivers/staging/android/ion/ion.c b/drivers/staging/android/ion/ion.c
> index 3d5bf14722..f55f61a4cc 100644
> --- a/drivers/staging/android/ion/ion.c
> +++ b/drivers/staging/android/ion/ion.c
> @@ -626,6 +626,10 @@ static void ion_handle_kmap_put(struct ion_handle *handle)
>  {
>         struct ion_buffer *buffer = handle->buffer;
>
> +       if (!handle->kmap_cnt) {
> +               WARN(1, "%s: Double unmap detected! bailing...\n", __func__);
> +               return;
> +       }
>         handle->kmap_cnt--;
>         if (!handle->kmap_cnt)
>                 ion_buffer_kmap_put(buffer);
> --
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Acked-by: Colin Cross <ccross@xxxxxxxxxxx>
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