[PATCH] sata_dwc_460ex: Fix missing check in sata_dwc_isr

[Dinghao Liu]

ata_qc_from_tag() may return a null pointer and further lead to
null-pointer-dereference. Add a return value check to avoid such case.

Signed-off-by: Dinghao Liu <dinghao.liu@xxxxxxxxxx>
---
 drivers/ata/sata_dwc_460ex.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/ata/sata_dwc_460ex.c b/drivers/ata/sata_dwc_460ex.c
index 9dcef6ac643b..0068247ffc06 100644
--- a/drivers/ata/sata_dwc_460ex.c
+++ b/drivers/ata/sata_dwc_460ex.c
@@ -548,8 +548,10 @@ static irqreturn_t sata_dwc_isr(int irq, void *dev_instance)
 		 * active tag.  It is the tag that matches the command about to
 		 * be completed.
 		 */
-		qc->ap->link.active_tag = tag;
-		sata_dwc_bmdma_start_by_tag(qc, tag);
+		if (qc) {
+			qc->ap->link.active_tag = tag;
+			sata_dwc_bmdma_start_by_tag(qc, tag);
+		}
 
 		handled = 1;
 		goto DONE;
-- 
2.17.1