media: amphion: Fix race between m2m job_abort and device_run

commit 8cd35ce upstream.

Fix kernel panic caused by race condition where v4l2_m2m_ctx_release()
frees m2m_ctx while v4l2_m2m_try_run() is about to call device_run
with the same context.

Race sequence:
  v4l2_m2m_try_run():           v4l2_m2m_ctx_release():
    lock/unlock                   v4l2_m2m_cancel_job()
                                    job_abort()
                                      v4l2_m2m_job_finish()
                                  kfree(m2m_ctx)  <- frees ctx
    device_run()  <- use-after-free crash at 0x538

Crash trace:
  Unable to handle kernel read from unreadable memory at virtual address
  0000000000000538
  v4l2_m2m_try_run+0x78/0x138
  v4l2_m2m_device_run_work+0x14/0x20

The amphion vpu driver does not rely on the m2m framework's device_run
callback to perform encode/decode operations.

Fix the race by preventing m2m framework job scheduling entirely:
- Add job_ready callback returning 0 (no jobs ready for m2m framework)
- Remove job_abort callback to avoid the race condition

Fixes: 3cd0845 ("media: amphion: add vpu v4l2 m2m support")
Cc: stable@vger.kernel.org
Signed-off-by: Ming Qian <ming.qian@oss.nxp.com>
Reviewed-by: Nicolas Dufresne <nicolas.dufresne@collabora.com>
Signed-off-by: Nicolas Dufresne <nicolas.dufresne@collabora.com>
Signed-off-by: Hans Verkuil <hverkuil+cisco@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: Ming Qian

drivers/media/platform/amphion/vpu_v4l2.c

@@ -441,17 +441,14 @@ static void vpu_m2m_device_run(void *priv)
 {
 }
 
-static void vpu_m2m_job_abort(void *priv)
+static int vpu_m2m_job_ready(void *priv)
 {
-	struct vpu_inst *inst = priv;
-	struct v4l2_m2m_ctx *m2m_ctx = inst->fh.m2m_ctx;
-
-	v4l2_m2m_job_finish(m2m_ctx->m2m_dev, m2m_ctx);
+	return 0;
 }
 
 static const struct v4l2_m2m_ops vpu_m2m_ops = {
 	.device_run = vpu_m2m_device_run,
-	.job_abort = vpu_m2m_job_abort
+	.job_ready = vpu_m2m_job_ready,
 };
 
 static int vpu_vb2_queue_setup(struct vb2_queue *vq,