Re: [PATCH v2] remoteproc: imx_dsp_rproc: Add mutex protection for workqueue

[Arnaud POULIQUEN <arnaud.pouliquen@foss.st.com>]

Hi Mathieu,

On 9/30/22 09:50, Shengjiu Wang wrote:
> The workqueue may execute late even after remoteproc is stopped or
> stopping, some resources (rpmsg device and endpoint) have been
> released in rproc_stop_subdevices(), then rproc_vq_interrupt()
> accessing these resources will cause kennel dump.
> 
> Call trace:
>  virtqueue_add_split+0x1ac/0x560
>  virtqueue_add_inbuf+0x4c/0x60
>  rpmsg_recv_done+0x15c/0x294
>  vring_interrupt+0x6c/0xa4
>  rproc_vq_interrupt+0x30/0x50
>  imx_dsp_rproc_vq_work+0x24/0x40 [imx_dsp_rproc]
>  process_one_work+0x1d0/0x354
>  worker_thread+0x13c/0x470
>  kthread+0x154/0x160
>  ret_from_fork+0x10/0x20
> 
> Add mutex protection in imx_dsp_rproc_vq_work(), if the state is
> not running, then just skip calling rproc_vq_interrupt().
> 
> Also the flush workqueue operation can't be added in rproc stop
> for the same reason. The call sequence is
> 
> rproc_shutdown
> -> rproc_stop
>    ->rproc_stop_subdevices
>    ->rproc->ops->stop()
>      ->imx_dsp_rproc_stop
>        ->flush_work
>          -> rproc_vq_interrupt
> 
> The resource needed by rproc_vq_interrupt has been released in
> rproc_stop_subdevices, so flush_work is not safe to be called in
> imx_dsp_rproc_stop.
> 
> Fixes: ec0e5549f358 ("remoteproc: imx_dsp_rproc: Add remoteproc driver for DSP on i.MX")
> Signed-off-by: Shengjiu Wang <shengjiu.wang@nxp.com>
> Reviewed-by: Peng Fan <peng.fan@nxp.com>
> ---
> changes in v2:
> - update commit message
> 
>  drivers/remoteproc/imx_dsp_rproc.c | 12 +++++++++---
>  1 file changed, 9 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/remoteproc/imx_dsp_rproc.c b/drivers/remoteproc/imx_dsp_rproc.c
> index 899aa8dd12f0..95da1cbefacf 100644
> --- a/drivers/remoteproc/imx_dsp_rproc.c
> +++ b/drivers/remoteproc/imx_dsp_rproc.c
> @@ -347,9 +347,6 @@ static int imx_dsp_rproc_stop(struct rproc *rproc)
>  	struct device *dev = rproc->dev.parent;
>  	int ret = 0;
>  
> -	/* Make sure work is finished */
> -	flush_work(&priv->rproc_work);
> -
>  	if (rproc->state == RPROC_CRASHED) {
>  		priv->flags &= ~REMOTE_IS_READY;
>  		return 0;
> @@ -432,9 +429,18 @@ static void imx_dsp_rproc_vq_work(struct work_struct *work)
>  {
>  	struct imx_dsp_rproc *priv = container_of(work, struct imx_dsp_rproc,
>  						  rproc_work);
> +	struct rproc *rproc = priv->rproc;
> +
> +	mutex_lock(&rproc->lock);
> +
> +	if (rproc->state != RPROC_RUNNING)
> +		goto unlock_mutex;
>  
>  	rproc_vq_interrupt(priv->rproc, 0);
>  	rproc_vq_interrupt(priv->rproc, 1);
> +
> +unlock_mutex:
> +	mutex_unlock(&rproc->lock);
>  }

I guess that this fix the issue in case of the use of a work queue for the
notification.

As I reproduced the issue on stm32 only one time without fix,
difficult for me to test the fix...

I also have a look on some other drivers
It seems not applicable for some other drivers such as TI k3 R5[1]
that call virtio under interrupt context ( if I have well understood).

An alternative to try to fix that in a more generic way could be to call
rproc_remove_virtio_dev in the subdev->unprepare, instead of subdev->stop.
This should postpone the virtio unregister after the stop of the coprocessor.

Of course it is only a suggestion/area of improvement, this fix LGTM.

[1]https://elixir.bootlin.com/linux/v6.0/source/drivers/remoteproc/ti_k3_r5_remoteproc.c#L180

Regards,
Arnaud


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