scsi: sr avoids useless buffer allocation

blk_rq_map_kern can handle the stack buffers correctly (avoid DMA
from/to the stack buffers by using the bounce buffer) so we don't need
to complicate the code by allocating just 8 bytes.
Signed-off-by: NFUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Cc: James Bottomley <James.Bottomley@HansenPartnership.com>
Cc: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Cc: Tejun Heo <htejun@gmail.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NJens Axboe <jens.axboe@oracle.com>

drivers/scsi/sr.c

@@ -673,24 +673,20 @@ static int sr_probe(struct device *dev)
 static void get_sectorsize(struct scsi_cd *cd)
 {
 	unsigned char cmd[10];
-	unsigned char *buffer;
+	unsigned char buffer[8];
 	int the_result, retries = 3;
 	int sector_size;
 	struct request_queue *queue;
 
-	buffer = kmalloc(512, GFP_KERNEL | GFP_DMA);
-	if (!buffer)
-		goto Enomem;
-
 	do {
 		cmd[0] = READ_CAPACITY;
 		memset((void *) &cmd[1], 0, 9);
-		memset(buffer, 0, 8);
+		memset(buffer, 0, sizeof(buffer));
 
 		/* Do the command and wait.. */
 		the_result = scsi_execute_req(cd->device, cmd, DMA_FROM_DEVICE,
-					      buffer, 8, NULL, SR_TIMEOUT,
-					      MAX_RETRIES);
+					      buffer, sizeof(buffer), NULL,
+					      SR_TIMEOUT, MAX_RETRIES);
 
 		retries--;
 
@@ -745,14 +741,8 @@ static void get_sectorsize(struct scsi_cd *cd)
 
 	queue = cd->device->request_queue;
 	blk_queue_hardsect_size(queue, sector_size);
-out:
-	kfree(buffer);
-	return;
 
-Enomem:
-	cd->capacity = 0x1fffff;
-	cd->device->sector_size = 2048;	/* A guess, just in case */
-	goto out;
+	return;
 }
 
 static void get_capabilities(struct scsi_cd *cd)