Re: [PATCH v3 03/11] media: videobuf2: Remove VB2_MAX_FRAME limit on buffer storage

From: Benjamin Gaignard <benjamin.gaignard@collabora.com>
To: Hans Verkuil <hverkuil-cisco@xs4all.nl>,
	Dan Carpenter <dan.carpenter@linaro.org>
Cc: 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, 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
Subject: Re: [PATCH v3 03/11] media: videobuf2: Remove VB2_MAX_FRAME limit on buffer storage
Date: Fri, 23 Jun 2023 09:51:29 +0200	[thread overview]
Message-ID: <fee4a434-a4b6-9ecc-1188-4638a3cd6af8@collabora.com> (raw)
In-Reply-To: <f21d6fce-155c-28f0-fdea-e9264ba1f7ba@xs4all.nl>

Le 23/06/2023 à 09:02, Hans Verkuil a écrit :
> On 22/06/2023 16:13, Benjamin Gaignard wrote:
>> Le 22/06/2023 à 16:11, Dan Carpenter a écrit :
>>> On Thu, Jun 22, 2023 at 03:13:41PM +0200, Benjamin Gaignard wrote:
>>>> diff --git a/drivers/media/common/videobuf2/videobuf2-core.c b/drivers/media/common/videobuf2/videobuf2-core.c
>>>> index f1ff7af34a9f..86e1e926fa45 100644
>>>> --- a/drivers/media/common/videobuf2/videobuf2-core.c
>>>> +++ b/drivers/media/common/videobuf2/videobuf2-core.c
>>>> @@ -455,9 +455,9 @@ static int __vb2_queue_alloc(struct vb2_queue *q, enum vb2_memory memory,
>>>>        struct vb2_buffer *vb;
>>>>        int ret;
>>>>    -    /* Ensure that q->num_buffers+num_buffers is below VB2_MAX_FRAME */
>>>> +    /* Ensure that q->num_buffers + num_buffers is UINT_MAX */
>>>>        num_buffers = min_t(unsigned int, num_buffers,
>>>> -                VB2_MAX_FRAME - q->num_buffers);
>>>> +                UINT_MAX - q->num_buffers);
>>>>          for (buffer = 0; buffer < num_buffers; ++buffer) {
>>>>            /* Allocate vb2 buffer structures */
>>> Ah...  Here's one of the integer overflow bugs I was talking about.  The
>>> __vb2_queue_alloc() function returns an int so if num_buffers goes over
>>> INT_MAX we are hosed.
>> I will limit it to:
>> #define VB2_QUEUE_MAX_BUFFERS  (INT_MAX & PAGE_MASK)  /* The mask prevents 85% of integer overflows */
>> as you have suggest it.
> IMHO INT_MAX is way overkill. How about (1U << 20)? I would like some sort of
> sanity check here. 1048576 buffers of 640x480 and 4 bytes per pixel is 1.2 TB.

I will go for (1U << 20) in next version.

Regards,
Benjamin

>
> Since a TB of memory is doable these days, I think this is a reasonable
> value for MAX_BUFFERS without allowing just anything.
>
> An alternative is to make this a kernel config.
>
> Regards,
>
> 	Hans
>
>> That will be in version 4.
>>
>> Thanks,
>> Benjamin
>>
>>> regards,
>>> dan carpenter
>>>

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