2 files changed, 25 insertions, 3 deletions

diff --git a/Documentation/usb/URB.txt b/Documentation/usb/URB.txt
index 8ffce746d496..00d2c644068e 100644
--- a/Documentation/usb/URB.txt
+++ b/Documentation/usb/URB.txt
@@ -168,6 +168,28 @@ that if the completion handler or anyone else tries to resubmit it
 they will get a -EPERM error.  Thus you can be sure that when
 usb_kill_urb() returns, the URB is totally idle.
 
+There is a lifetime issue to consider.  An URB may complete at any
+time, and the completion handler may free the URB.  If this happens
+while usb_unlink_urb or usb_kill_urb is running, it will cause a
+memory-access violation.  The driver is responsible for avoiding this,
+which often means some sort of lock will be needed to prevent the URB
+from being deallocated while it is still in use.
+
+On the other hand, since usb_unlink_urb may end up calling the
+completion handler, the handler must not take any lock that is held
+when usb_unlink_urb is invoked.  The general solution to this problem
+is to increment the URB's reference count while holding the lock, then
+drop the lock and call usb_unlink_urb or usb_kill_urb, and then
+decrement the URB's reference count.  You increment the reference
+count by calling
+
+        struct urb *usb_get_urb(struct urb *urb)
+
+(ignore the return value; it is the same as the argument) and
+decrement the reference count by calling usb_free_urb.  Of course,
+none of this is necessary if there's no danger of the URB being freed
+by the completion handler.
+
 
 1.7. What about the completion handler?
 
diff --git a/Documentation/usb/usbmon.txt b/Documentation/usb/usbmon.txt
index 5335fa8b06eb..c42bb9cd3b43 100644
--- a/Documentation/usb/usbmon.txt
+++ b/Documentation/usb/usbmon.txt
@@ -183,10 +183,10 @@ An input control transfer to get a port status.
 d5ea89a0 3575914555 S Ci:1:001:0 s a3 00 0000 0003 0004 4 <
 d5ea89a0 3575914560 C Ci:1:001:0 0 4 = 01050000
 
-An output bulk transfer to send a SCSI command 0x5E in a 31-byte Bulk wrapper
-to a storage device at address 5:
+An output bulk transfer to send a SCSI command 0x28 (READ_10) in a 31-byte
+Bulk wrapper to a storage device at address 5:
 
-dd65f0e8 4128379752 S Bo:1:005:2 -115 31 = 55534243 5e000000 00000000 00000600 00000000 00000000 00000000 000000
+dd65f0e8 4128379752 S Bo:1:005:2 -115 31 = 55534243 ad000000 00800000 80010a28 20000000 20000040 00000000 000000
 dd65f0e8 4128379808 C Bo:1:005:2 0 31 >
 
 * Raw binary format and API