linux-kernel - Re: [PATCH v7 45/49] media: core: Add bitmap manage bufs array entries

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Date:   Wed, 20 Sep 2023 17:17:40 +0200
From:   Benjamin Gaignard <benjamin.gaignard@...labora.com>
To:     Hans Verkuil <hverkuil-cisco@...all.nl>, mchehab@...nel.org,
        tfiga@...omium.org, m.szyprowski@...sung.com, ming.qian@....com,
        ezequiel@...guardiasur.com.ar, p.zabel@...gutronix.de,
        gregkh@...uxfoundation.org, nicolas.dufresne@...labora.com
Cc:     linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, linux-arm-msm@...r.kernel.org,
        linux-rockchip@...ts.infradead.org, linux-staging@...ts.linux.dev,
        kernel@...labora.com
Subject: Re: [PATCH v7 45/49] media: core: Add bitmap manage bufs array
 entries


Le 20/09/2023 à 16:56, Hans Verkuil a écrit :
> On 20/09/2023 16:30, Benjamin Gaignard wrote:
> <snip>
>
>>>>        num_buffers = min_t(unsigned int, num_buffers,
>>>>                    q->max_allowed_buffers - vb2_get_num_buffers(q));
>>>>    -    first_index = vb2_get_num_buffers(q);
>>>> +    first_index = bitmap_find_next_zero_area(q->bufs_map, q->max_allowed_buffers,
>>>> +                         0, num_buffers, 0);
>>>>          if (first_index >= q->max_allowed_buffers)
>>>>            return 0;
>>>> @@ -675,7 +678,13 @@ static void __vb2_queue_free(struct vb2_queue *q, unsigned int buffers)
>>>>      struct vb2_buffer *vb2_get_buffer(struct vb2_queue *q, unsigned int index)
>>>>    {
>>>> -    if (index < q->num_buffers)
>>>> +    if (!q->bufs_map || !q->bufs)
>>>> +        return NULL;
>>> I don't think this can ever happen.
>> I got kernel crash without them.
>> I will keep them.
> What is the backtrace? How can this happen? It feels wrong that this can be
> called with a vb2_queue that apparently is not properly initialized.

I will add backtrace when doing test on v8

>
>
>>>> +
>>>> +    return (bitmap_weight(q->bufs_map, q->max_allowed_buffers) > 0);
>>> How about:
>>>
>>>      return vb2_get_num_buffers(q) > 0;
>> vb2_get_num_buffers is defined in videobuf2-core.c, I'm not sure that
>> an inline function could depend of a module function.
> Not a problem. E.g. v4l2-ctrls.h is full of such static inlines.

I will change vb2_get_num_buffers() to inline function that solve the problem too.

>
> Regards,
>
> 	Hans
>