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

Mathieu Poirier
2022-09-28T17:21:00Z

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
>