usblp: mutex in usblp_check_status

Add a mutex to protect the ->statusbuf. Not really an issue, because CUPS
is single-threaded when it talks to the printer, but I feel safer this way.
This should be deadlock-free, but I kept this as a separate patch in case
someone ends running a git bisect.

Signed-off-by: Pete Zaitcev <[email protected]>

--- linux-2.6.23-rc3-gregkh/drivers/usb/class/usblp.c	2007-08-13 22:44:06.000000000 -0700
+++ linux-2.6.23-rc2-mon/drivers/usb/class/usblp.c	2007-08-05 22:54:42.000000000 -0700
@@ -345,16 +346,17 @@ static int usblp_check_status(struct usb
 	unsigned char status, newerr = 0;
 	int error;
 
-	error = usblp_read_status (usblp, usblp->statusbuf);
-	if (error < 0) {
+	mutex_lock(&usblp->mut);
+	if ((error = usblp_read_status(usblp, usblp->statusbuf)) < 0) {
+		mutex_unlock(&usblp->mut);
 		if (printk_ratelimit())
 			printk(KERN_ERR
 				"usblp%d: error %d reading printer status\n",
 				usblp->minor, error);
 		return 0;
 	}
-
 	status = *usblp->statusbuf;
+	mutex_unlock(&usblp->mut);
 
 	if (~status & LP_PERRORP)
 		newerr = 3;

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