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

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Message-ID: <470682b4-c14b-4237-bc46-fddfdd085026@xs4all.nl>
Date:   Wed, 20 Sep 2023 16:56:27 +0200
From:   Hans Verkuil <hverkuil-cisco@...all.nl>
To:     Benjamin Gaignard <benjamin.gaignard@...labora.com>,
        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

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.

>>> +
>>> +    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.

Regards,

	Hans