linux-kernel - Re: [PATCH v1 1/3] media: cedrus: Fix watchdog race condition

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Message-ID: <YwM4efK9V4t38RFe@aptenodytes>
Date:   Mon, 22 Aug 2022 10:04:09 +0200
From:   Paul Kocialkowski <paul.kocialkowski@...tlin.com>
To:     Nicolas Dufresne <nicolas.dufresne@...labora.com>
Cc:     linux-media@...r.kernel.org, Maxime Ripard <mripard@...nel.org>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Chen-Yu Tsai <wens@...e.org>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        Samuel Holland <samuel@...lland.org>,
        Ezequiel Garcia <ezequiel@...guardiasur.com.ar>,
        Hans Verkuil <hverkuil-cisco@...all.nl>, kernel@...labora.com,
        stable@...r.kernel.org, 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 1/3] media: cedrus: Fix watchdog race condition

Hi Nicolas,

On Thu 18 Aug 22, 16:33, Nicolas Dufresne wrote:
> The watchdog needs to be schedule before we trigger the decode
> operation, otherwise there is a risk that the decoder IRQ will be
> called before we have schedule the watchdog. As a side effect, the
> watchdog would never be cancelled and its function would be called
> at an inappropriate time.
> 
> This was observed while running Fluster with GStreamer as a backend.
> Some programming error would cause the decoder IRQ to be call very
> quickly after the trigger. Later calls into the driver would deadlock
> due to the unbalanced state.

Good catch, thanks!

Reviewed-by: Paul Kocialkowski <paul.kocialkowski@...tlin.com>

Cheers,

Paul

> Cc: stable@...r.kernel.org
> Fixes: 7c38a551bda1 ("media: cedrus: Add watchdog for job completion")
> Signed-off-by: Nicolas Dufresne <nicolas.dufresne@...labora.com>
> ---
>  drivers/staging/media/sunxi/cedrus/cedrus_dec.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/staging/media/sunxi/cedrus/cedrus_dec.c b/drivers/staging/media/sunxi/cedrus/cedrus_dec.c
> index 3b6aa78a2985f..e7f7602a5ab40 100644
> --- a/drivers/staging/media/sunxi/cedrus/cedrus_dec.c
> +++ b/drivers/staging/media/sunxi/cedrus/cedrus_dec.c
> @@ -106,11 +106,11 @@ void cedrus_device_run(void *priv)
>  
>  	/* Trigger decoding if setup went well, bail out otherwise. */
>  	if (!error) {
> -		dev->dec_ops[ctx->current_codec]->trigger(ctx);
> -
>  		/* Start the watchdog timer. */
>  		schedule_delayed_work(&dev->watchdog_work,
>  				      msecs_to_jiffies(2000));
> +
> +		dev->dec_ops[ctx->current_codec]->trigger(ctx);
>  	} else {
>  		v4l2_m2m_buf_done_and_job_finish(ctx->dev->m2m_dev,
>  						 ctx->fh.m2m_ctx,
> -- 
> 2.37.2
> 

-- 
Paul Kocialkowski, Bootlin
Embedded Linux and kernel engineering
https://bootlin.com

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