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Date:   Thu, 21 Sep 2023 12:24:08 +0200
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Subject: Re: [PATCH v7 45/49] media: core: Add bitmap manage bufs array
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To:     Benjamin Gaignard <benjamin.gaignard@collabora.com>,
        mchehab@kernel.org, tfiga@chromium.org, m.szyprowski@samsung.com,
        ming.qian@nxp.com, ezequiel@vanguardiasur.com.ar,
        p.zabel@pengutronix.de, gregkh@linuxfoundation.org,
        nicolas.dufresne@collabora.com
Cc:     linux-media@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org,
        linux-mediatek@lists.infradead.org, linux-arm-msm@vger.kernel.org,
        linux-rockchip@lists.infradead.org, linux-staging@lists.linux.dev,
        kernel@collabora.com
References: <20230914133323.198857-1-benjamin.gaignard@collabora.com>
 <20230914133323.198857-46-benjamin.gaignard@collabora.com>
 <1142bbb4-b8f1-44ec-962e-9347a231782f@xs4all.nl>
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 <31f298ec-6280-d21b-3d8a-c7bf1c9c0c30@collabora.com>
From:   Hans Verkuil <hverkuil-cisco@xs4all.nl>
In-Reply-To: <31f298ec-6280-d21b-3d8a-c7bf1c9c0c30@collabora.com>
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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.

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
>>