3.0-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Xiaotian Feng <redacted>

commit 26cd4d65deba587f3cf2329b6869ce02bcbe68ec upstream.

Following oops were observed when disk error happened:

[ 4272.896937] sd 0:0:0:0: [sda] Unhandled error code
[ 4272.896939] sd 0:0:0:0: [sda] Result: hostbyte=DID_BAD_TARGET driverbyte=DRIVER_OK
[ 4272.896942] sd 0:0:0:0: [sda] CDB: Read(10): 28 00 00 5a de a7 00 00 08 00
[ 4272.896951] end_request: I/O error, dev sda, sector 5955239
[ 4291.574947] BUG: unable to handle kernel NULL pointer dereference at (null)
[ 4291.658305] IP: [] ahci_activity_show+0x1/0x40
[ 4291.730090] PGD 76dbbc067 PUD 6c4fba067 PMD 0
[ 4291.783408] Oops: 0000 [#1] SMP
[ 4291.822100] last sysfs file: /sys/devices/pci0000:00/0000:00:1f.2/host0/target0:0:0/0:0:0:0/sw_activity
[ 4291.934235] CPU 9
[ 4291.958301] Pid: 27942, comm: hwinfo ......

ata_scsi_find_dev could return NULL, so ata_scsi_activity_{show,store} should check if atadev is NULL.

Signed-off-by: Xiaotian Feng <redacted>
Cc: James Bottomley <redacted>
Signed-off-by: Jeff Garzik <redacted>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/ata/libata-scsi.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

--- a/drivers/ata/libata-scsi.c
+++ b/drivers/ata/libata-scsi.c

@@ -308,7 +308,8 @@ ata_scsi_activity_show(struct device *de
 	struct ata_port *ap = ata_shost_to_port(sdev->host);
 	struct ata_device *atadev = ata_scsi_find_dev(ap, sdev);
 
-	if (ap->ops->sw_activity_show && (ap->flags & ATA_FLAG_SW_ACTIVITY))
+	if (atadev && ap->ops->sw_activity_show &&
+	    (ap->flags & ATA_FLAG_SW_ACTIVITY))
 		return ap->ops->sw_activity_show(atadev, buf);
 	return -EINVAL;
 }

@@ -323,7 +324,8 @@ ata_scsi_activity_store(struct device *d
 	enum sw_activity val;
 	int rc;
 
-	if (ap->ops->sw_activity_store && (ap->flags & ATA_FLAG_SW_ACTIVITY)) {
+	if (atadev && ap->ops->sw_activity_store &&
+	    (ap->flags & ATA_FLAG_SW_ACTIVITY)) {
 		val = simple_strtoul(buf, NULL, 0);
 		switch (val) {
 		case OFF: case BLINK_ON: case BLINK_OFF: