Re: [PATCH v2 6/8] media: platform: amd: isp4 video node and buffers handling added

Du, Bin
2025-07-29T06:13:11Z

Many thanks Sultan, will try your changes in this and other mails
together and let you know the result

On 7/27/2025 5:50 AM, Sultan Alsawaf wrote:
> On Sat, Jul 26, 2025 at 02:41:41PM -0700, Sultan Alsawaf wrote:
>> On Fri, Jul 25, 2025 at 05:22:41PM +0800, Du, Bin wrote:
>>>>> + dev_warn(buf->dev, "ignore buffer free, refcount %u > 0",
>>>>> + refcount_read(&buf->refcount));
>>>>
>>>> This refcount_read() is a possible use-after-free because `buf` is accessed
>>>> after isp4vid_vb2_put() puts its reference to `buf`. So something else could put
>>>> the last reference to `buf` and free it after this refcount dec but before the
>>>> refcount_read(). Maybe just remove this dev_warn() entirely?
>>>>
>>> The warning is important to debug mem related issue, plan to keep it but
>>> without accessing buf or buf->refcount here. Do you think it acceptible?
>>
>> Yes, that sounds good. So something like this:
>> `dev_warn(buf->dev, "ignore buffer free, refcount > 0");`
>
> Sorry, to fix the dev_warn() we need to make a copy of buf->dev first:
>
> --- a/drivers/media/platform/amd/isp4/isp4_video.c
> +++ b/drivers/media/platform/amd/isp4/isp4_video.c
> @@ -584,8 +584,9 @@ static void isp4vid_vb2_put(void *buf_priv)
> {
> struct isp4vid_vb2_buf *buf = (struct isp4vid_vb2_buf *)buf_priv;
> struct amdgpu_bo *bo = (struct amdgpu_bo *)buf->bo;
> + struct device *dev = buf->dev;
>
> - dev_dbg(buf->dev,
> + dev_dbg(dev,
> "release isp user bo 0x%llx size %ld refcount %d is_expbuf %d",
> buf->gpu_addr, buf->size,
> buf->refcount.refs.counter, buf->is_expbuf);
> @@ -601,8 +602,7 @@ static void isp4vid_vb2_put(void *buf_priv)
> kfree(buf);
> buf = NULL;
> } else {
> - dev_warn(buf->dev, "ignore buffer free, refcount %u > 0",
> - refcount_read(&buf->refcount));
> + dev_warn(dev, "ignore buffer free, refcount > 0\n");
> }
> }
>
> --
>
> Sultan