[SCSI] sd name space exhaustion causes system hang

Following a site power outage which re-enabled all the ports on my FC
switches, my system subsequently booted with far too many luns!  I had
let it run hoping it would make multi-user.  It didn't.  :(  It hung solid
after exhausting the last sd device, sdzzz, and attempting to create sdaaaa
and beyond.  I was unable to get a dump.

Discovered using a 2.6.32.13 based system.

correct this by detecting when the last index is utilized and failing
the sd probe of the device.  Patch applies to scsi-misc-2.6.
Signed-off-by: Michael Reed <mdr@sgi.com>
Cc: Stable Tree <stable@kernel.org>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>

drivers/scsi/sd.c

@@ -2288,11 +2288,10 @@ static void sd_probe_async(void *data, async_cookie_t cookie)
 	index = sdkp->index;
 	dev = &sdp->sdev_gendev;
 
-	if (index < SD_MAX_DISKS) {
-		gd->major = sd_major((index & 0xf0) >> 4);
-		gd->first_minor = ((index & 0xf) << 4) | (index & 0xfff00);
-		gd->minors = SD_MINORS;
-	}
+	gd->major = sd_major((index & 0xf0) >> 4);
+	gd->first_minor = ((index & 0xf) << 4) | (index & 0xfff00);
+	gd->minors = SD_MINORS;
+
 	gd->fops = &sd_fops;
 	gd->private_data = &sdkp->driver;
 	gd->queue = sdkp->device->request_queue;
@@ -2382,6 +2381,12 @@ static int sd_probe(struct device *dev)
 	if (error)
 		goto out_put;
 
+	if (index >= SD_MAX_DISKS) {
+		error = -ENODEV;
+		sdev_printk(KERN_WARNING, sdp, "SCSI disk (sd) name space exhausted.\n");
+		goto out_free_index;
+	}
+
 	error = sd_format_disk_name("sd", index, gd->disk_name, DISK_NAME_LEN);
 	if (error)
 		goto out_free_index;