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 <zaitcev@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 4 insertions, 3 deletions

diff --git a/drivers/usb/class/usblp.c b/drivers/usb/class/usblp.c
index 9696668e5752..2c4a359355ba 100644
--- a/drivers/usb/class/usblp.c
+++ b/drivers/usb/class/usblp.c
@@ -345,16 +345,17 @@ static int usblp_check_status(struct usblp *usblp, int err)
         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;