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

[Mathieu Poirier <mathieu.poirier@linaro.org>]

On Mon, Sep 26, 2022 at 07:48:13PM +0800, 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()
> access 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 same reason.
> 
> Fixes: ec0e5549f358 ("remoteproc: imx_dsp_rproc: Add remoteproc driver for DSP on i.MX")
> Signed-off-by: Shengjiu Wang <shengjiu.wang@nxp.com>
> ---
>  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);
> -

The kernel documentation for this function [1] indicate that once it returns
there will no more jobs to process in that queue, _unless_ another job has been
queued _after_ the flush has started.  What I suspect is happening here is that
a new job is queued between the time flush_work() returns and the remote processor
is switched off, something that should not be happening since all the
subdevices have been stopped in rproc_stop_subdevices().  

[1]. https://elixir.bootlin.com/linux/v6.0-rc7/source/kernel/workqueue.c#L3092


>  	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);

These are not guaranteed to be atomic and sleeping with the mutex held is
guaranteed to deadlock the system.

Thanks,
Mathieu

> +
> +unlock_mutex:
> +	mutex_unlock(&rproc->lock);
>  }
>  
>  /**
> -- 
> 2.34.1
>