[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....@zju.edu.cn>
---
 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