mmc: sh-mmcif: avoid oops on spurious interrupts (second try)

On some systems, e.g., kzm9g, MMCIF interfaces can produce spurious
interrupts without any active request. To prevent the Oops, that results
in such cases, don't dereference the mmc request pointer until we make
sure, that we are indeed processing such a request.

Reported-by: Tetsuyuki Kobayashi <koba@kmckk.co.jp>
Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Tested-by: Tetsuyuki Kobayashi <koba@kmckk.co.jp>
Cc: stable@vger.kernel.org
Signed-off-by: Chris Ball <cjb@laptop.org>

drivers/mmc/host/sh_mmcif.c

@@ -1104,7 +1104,6 @@ static irqreturn_t sh_mmcif_irqt(int irq, void *dev_id)
 {
 	struct sh_mmcif_host *host = dev_id;
 	struct mmc_request *mrq = host->mrq;
-	struct mmc_data *data = mrq->data;
 
 	cancel_delayed_work_sync(&host->timeout_work);
 
@@ -1152,13 +1151,14 @@ static irqreturn_t sh_mmcif_irqt(int irq, void *dev_id)
 	case MMCIF_WAIT_FOR_READ_END:
 	case MMCIF_WAIT_FOR_WRITE_END:
 		if (host->sd_error)
-			data->error = sh_mmcif_error_manage(host);
+			mrq->data->error = sh_mmcif_error_manage(host);
 		break;
 	default:
 		BUG();
 	}
 
 	if (host->wait_for != MMCIF_WAIT_FOR_STOP) {
+		struct mmc_data *data = mrq->data;
 		if (!mrq->cmd->error && data && !data->error)
 			data->bytes_xfered =
 				data->blocks * data->blksz;