block,scsi: verify return pointer from blk_get_request

The blk-core dead queue checks introduce an error scenario to
blk_get_request that returns NULL if the request queue has been
shutdown. This affects the behavior for __GFP_WAIT callers, who should
verify the return value before dereferencing.
Signed-off-by: Joe Lawrence <joe.lawrence@stratus.com>
Acked-by: Jiri Kosina <jkosina@suse.cz> [for pktdvd]
Reviewed-by: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

block/scsi_ioctl.c

@@ -448,6 +448,10 @@ int sg_scsi_ioctl(struct request_queue *q, struct gendisk *disk, fmode_t mode,
 	}
 
 	rq = blk_get_request(q, in_len ? WRITE : READ, __GFP_WAIT);
+	if (!rq) {
+		err = -ENODEV;
+		goto error_free_buffer;
+	}
 
 	cmdlen = COMMAND_SIZE(opcode);
 
@@ -520,8 +524,9 @@ int sg_scsi_ioctl(struct request_queue *q, struct gendisk *disk, fmode_t mode,
 	}
 	
 error:
-	kfree(buffer);
 	blk_put_request(rq);
+error_free_buffer:
+	kfree(buffer);
 	return err;
 }
 EXPORT_SYMBOL_GPL(sg_scsi_ioctl);
@@ -534,6 +539,8 @@ static int __blk_send_generic(struct request_queue *q, struct gendisk *bd_disk,
 	int err;
 
 	rq = blk_get_request(q, WRITE, __GFP_WAIT);
+	if (!rq)
+		return -ENODEV;
 	blk_rq_set_block_pc(rq);
 	rq->timeout = BLK_DEFAULT_SG_TIMEOUT;
 	rq->cmd[0] = cmd;

drivers/block/paride/pd.c

@@ -722,6 +722,8 @@ static int pd_special_command(struct pd_unit *disk,
 	int err = 0;
 
 	rq = blk_get_request(disk->gd->queue, READ, __GFP_WAIT);
+	if (!rq)
+		return -ENODEV;
 
 	rq->cmd_type = REQ_TYPE_SPECIAL;
 	rq->special = func;

drivers/block/pktcdvd.c

@@ -704,6 +704,8 @@ static int pkt_generic_packet(struct pktcdvd_device *pd, struct packet_command *
 
 	rq = blk_get_request(q, (cgc->data_direction == CGC_DATA_WRITE) ?
 			     WRITE : READ, __GFP_WAIT);
+	if (!rq)
+		return -ENODEV;
 	blk_rq_set_block_pc(rq);
 
 	if (cgc->buflen) {

drivers/scsi/scsi_error.c

@@ -1960,6 +1960,8 @@ static void scsi_eh_lock_door(struct scsi_device *sdev)
 	 * request becomes available
 	 */
 	req = blk_get_request(sdev->request_queue, READ, GFP_KERNEL);
+	if (!req)
+		return;
 
 	blk_rq_set_block_pc(req);