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

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Message-ID: <aa649adf-8faf-801b-f6bd-d4a4760e040f@collabora.com>
Date:   Thu, 21 Sep 2023 14:05:32 +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 21/09/2023 à 12:24, Hans Verkuil a écrit :
> On 21/09/2023 11:28, Benjamin Gaignard wrote:
>> 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 have this log when adding dump_stack() in vb2_get_buffer() if !q->bufs_bitmap:
>>
>> [   18.924627] Call trace:
>> [   18.927090]  dump_backtrace+0x94/0xec
>> [   18.930787]  show_stack+0x18/0x24
>> [   18.934137]  dump_stack_lvl+0x48/0x60
>> [   18.937833]  dump_stack+0x18/0x24
>> [   18.941166]  __vb2_queue_cancel+0x23c/0x2f0
>> [   18.945365]  vb2_core_queue_release+0x24/0x6c
>> [   18.949740]  vb2_queue_release+0x10/0x1c
>> [   18.953677]  v4l2_m2m_ctx_release+0x20/0x40
>> [   18.957892]  hantro_release+0x20/0x54
>> [   18.961584]  v4l2_release+0x74/0xec
>> [   18.965110]  __fput+0xb4/0x274
>> [   18.968205]  __fput_sync+0x50/0x5c
>> [   18.971626]  __arm64_sys_close+0x38/0x7c
>> [   18.975562]  invoke_syscall+0x48/0x114
>> [   18.979329]  el0_svc_common.constprop.0+0xc0/0xe0
>> [   18.984068]  do_el0_svc+0x1c/0x28
>> [   18.987402]  el0_svc+0x40/0xe8
>> [   18.990470]  el0t_64_sync_handler+0x100/0x12c
>> [   18.994842]  el0t_64_sync+0x190/0x194
>>
>> This happen at boot time when hantro driver is open and close without other actions.
> Ah, now I see the problem. q->bufs and q->bufs_map are allocated in
> vb2_core_create_bufs and vb2_core_reqbufs, but they should be allocated
> in vb2_queue_init: that's the counterpart of vb2_core_queue_release.
>
> With that change you shouldn't have to check for q->bufs/bufs_map anymore.

It is a better solution but even like this vb2_core_queue_release() is called
at least 2 times on the same vivid queue and without testing q->bufs_bitmap
makes kernel crash.

>
> Regards,
>
> 	Hans
>
>>     
>>>>>> +
>>>>>> +    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
>>>
>