remoteproc: imx_dsp_rproc: Add mutex protection for workqueue

remoteproc: imx_dsp_rproc: Add mutex protection for workqueue

commit 47e6ab07018edebf94ce873cf50a05ec76ff2dde upstream.

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>
Cc: stable <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/1664524216-19949-1-git-send-email-shengjiu.wang@nxp.com
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>