[PATCH]races in usblp

Hi,

usblp has an issue with urbs being resubmitted without status being read
first. In this case it is complicated by a race in the write path. Busy is
checked without a lock and the check not redone under lock.

	Regards
		Oliver
Signed-off-by: Oliver Neukum <[email protected]>
-- 

--- a/drivers/usb/class/usblp.c	2007-03-19 10:59:52.000000000 +0100
+++ b/drivers/usb/class/usblp.c	2007-03-30 11:01:47.000000000 +0200
@@ -286,6 +288,7 @@
 	if (unlikely(urb->status))
 		warn("usblp%d: nonzero read/write bulk status received: %d",
 			usblp->minor, urb->status);
+	smp_mb();
 	usblp->rcomplete = 1;
 unplug:
 	wake_up_interruptible(&usblp->wait);
@@ -302,6 +305,7 @@
 	if (unlikely(urb->status))
 		warn("usblp%d: nonzero read/write bulk status received: %d",
 			usblp->minor, urb->status);
+	smp_mb();
 	usblp->wcomplete = 1;
 unplug:
 	wake_up_interruptible(&usblp->wait);
@@ -666,7 +670,7 @@
 				writecount += transfer_length;
 				return writecount ? writecount : -EAGAIN;
 			}
-
+lost_race:
 			timeout = USBLP_WRITE_TIMEOUT;
 
 			rv = wait_event_interruptible_timeout(usblp->wait, usblp->wcomplete || !usblp->present , timeout);
@@ -686,6 +690,17 @@
 			return writecount ? writecount : -ENODEV;
 		}
 
+		/* need to recheck under lock */
+		if (!usblp->wcomplete) { /* lost the race to another thread */
+			mutex_unlock(&usblp->mut);
+			if (writecount) {
+				count = writecount;
+				break;
+			} else {
+				goto lost_race;
+			}
+		}
+
 		if (usblp->writeurb->status != 0) {
 			if (usblp->quirks & USBLP_QUIRK_BIDIR) {
 				if (!usblp->wcomplete)

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