media: coda: fix deadlock between decoder picture run and start command

The BIT decoder picture run temporarily locks the bitstream mutex while
the coda device mutex is locked, to refill the bitstream ring buffer.
Consequently, the decoder start command, which locks both mutexes when
flushing the bitstream ring buffer, must lock the coda device mutex
first as well, to avoid an ABBA deadlock.

Fixes: e7fd9584 ("media: coda: flush bitstream ring buffer on decoder restart")
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>

drivers/media/platform/coda/coda-common.c

@@ -1084,16 +1084,16 @@ static int coda_decoder_cmd(struct file *file, void *fh,
 
 	switch (dc->cmd) {
 	case V4L2_DEC_CMD_START:
-		mutex_lock(&ctx->bitstream_mutex);
 		mutex_lock(&dev->coda_mutex);
+		mutex_lock(&ctx->bitstream_mutex);
 		coda_bitstream_flush(ctx);
-		mutex_unlock(&dev->coda_mutex);
 		dst_vq = v4l2_m2m_get_vq(ctx->fh.m2m_ctx,
 					 V4L2_BUF_TYPE_VIDEO_CAPTURE);
 		vb2_clear_last_buffer_dequeued(dst_vq);
 		ctx->bit_stream_param &= ~CODA_BIT_STREAM_END_FLAG;
 		coda_fill_bitstream(ctx, NULL);
 		mutex_unlock(&ctx->bitstream_mutex);
+		mutex_unlock(&dev->coda_mutex);
 		break;
 	case V4L2_DEC_CMD_STOP:
 		stream_end = false;