linux-kernel - Re: [PATCH v1 3/3] media: cedrus: Fix endless loop in cedrus_h265_skip

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Date:   Fri, 19 Aug 2022 06:16:12 +0200
From:   Jernej Škrabec <jernej.skrabec@...il.com>
To:     linux-media@...r.kernel.org, Maxime Ripard <mripard@...nel.org>,
        Paul Kocialkowski <paul.kocialkowski@...tlin.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Chen-Yu Tsai <wens@...e.org>,
        Samuel Holland <samuel@...lland.org>,
        Nicolas Dufresne <nicolas.dufresne@...labora.com>
Cc:     kernel@...labora.com,
        Dmitry Osipenko <dmitry.osipenko@...labora.com>,
        stable@...r.kernel.org,
        Nicolas Dufresne <nicolas.dufresne@...labora.com>,
        linux-staging@...ts.linux.dev,
        linux-arm-kernel@...ts.infradead.org, linux-sunxi@...ts.linux.dev,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 3/3] media: cedrus: Fix endless loop in cedrus_h265_skip_bits()

Dne četrtek, 18. avgust 2022 ob 22:33:08 CEST je Nicolas Dufresne napisal(a):
> From: Dmitry Osipenko <dmitry.osipenko@...labora.com>
> 
> The busy status bit may never de-assert if number of programmed skip
> bits is incorrect, resulting in a kernel hang because the bit is polled
> endlessly in the code. Fix it by adding timeout for the bit-polling.
> This problem is reproducible by setting the data_bit_offset field of
> the HEVC slice params to a wrong value by userspace.
> 
> Cc: stable@...r.kernel.org
> Reported-by: Nicolas Dufresne <nicolas.dufresne@...labora.com>
> Signed-off-by: Dmitry Osipenko <dmitry.osipenko@...labora.com>
> Signed-off-by: Nicolas Dufresne <nicolas.dufresne@...labora.com>

Fixes tag would be nice.

> ---
>  drivers/staging/media/sunxi/cedrus/cedrus_h265.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/staging/media/sunxi/cedrus/cedrus_h265.c
> b/drivers/staging/media/sunxi/cedrus/cedrus_h265.c index
> f703c585d91c5..f0bc118021b0a 100644
> --- a/drivers/staging/media/sunxi/cedrus/cedrus_h265.c
> +++ b/drivers/staging/media/sunxi/cedrus/cedrus_h265.c
> @@ -227,6 +227,7 @@ static void cedrus_h265_pred_weight_write(struct
> cedrus_dev *dev, static void cedrus_h265_skip_bits(struct cedrus_dev *dev,
> int num) {
>  	int count = 0;
> +	u32 reg;
> 
>  	while (count < num) {
>  		int tmp = min(num - count, 32);
> @@ -234,8 +235,9 @@ static void cedrus_h265_skip_bits(struct cedrus_dev
> *dev, int num) cedrus_write(dev, VE_DEC_H265_TRIGGER,
>  			     VE_DEC_H265_TRIGGER_FLUSH_BITS |
>  			     VE_DEC_H265_TRIGGER_TYPE_N_BITS(tmp));
> -		while (cedrus_read(dev, VE_DEC_H265_STATUS) &
> VE_DEC_H265_STATUS_VLD_BUSY) -			udelay(1);
> +
> +		if (cedrus_wait_for(dev, VE_DEC_H265_STATUS,
> VE_DEC_H265_STATUS_VLD_BUSY)) +			
dev_err_ratelimited(dev->dev, "timed out
> waiting to skip bits\n");

Reporting issue is nice, but better would be to propagate error, since there 
is no way to properly decode this slice if above code block fails.

Best regards,
Jernej

> 
>  		count += tmp;
>  	}