Description of problem:

There are several race conditions in the 2.4.21 kernel nbd driver 
that can cause a kernel oops. A patch has been accepted by the 2.4 
kernel maintainer (Marcelo Tosatti) circa 2.4.22-preX release. The 
2.4.21 kernel in RHEL3 is susceptible to these problems. The patch to 
fix these problems is attached.

Specifically, the patch fixes the following problems:

1) adds locking and properly orders the code in NBD_CLEAR_SOCK to
eliminate races with other code
 
2) adds an lo->sock check to nbd_clear_que to eliminate races between
do_nbd_request and nbd_clear_que, which resulted in the dequeuing of
active requests
 
3) adds an lo->sock check to NBD_DO_IT to eliminate races with
NBD_CLEAR_SOCK, which caused an Oops when "nbd-client -d" was called
 
Version-Release number of selected component (if applicable):
kernel 2.4.21

How reproducible:
sometimes

Steps to Reproduce:
normal usage of nbd driver and utilities causes kernel oops

Actual results:
kernel oops

Expected results:
no kernel oops

Additional info: