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

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Message-ID: <31f298ec-6280-d21b-3d8a-c7bf1c9c0c30@collabora.com>
Date:   Thu, 21 Sep 2023 11:28:09 +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 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.
     

>
>>>> +
>>>> +    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
>