Red Hat Bugzilla – Bug 449809
gnbd race between sender and receiver process
Last modified: 2010-10-22 21:40:42 EDT
Description of problem:
It is possible to have the gnbd receiver process finish and end a request before
the sending process has finished using the request structure. This can cause a
Version-Release number of selected component (if applicable):
Not sure. It is possible that a customer has seen this.
This bug was originally mentioned in comment #14 of BZ #444074, but is possibly
unrelated to issue that bugzilla was opened to track.
The race can happen under the following conditions:
1. the request gets sent
2. reply comes in, the the receiver process frees up the request
3. now the sender process wakes up and tries to the kunmap, but because
the request block has already been freed-up, kunmap will crash.
Created attachment 308274 [details]
patch to wait before ending the request, if it is currently being sent.
This patch adds a waitqueue (tx_wait) and a pointer to the request currently
being send (current_request) to the gnbd device structure. current_request is
set before any request is sent to the server. When the send is complete, it is
cleared and the wait_queue is woken. A new function, wait_for_send() is called
whenever it is possible for a call to gnbd_end_request() to interleave with a
send. It waits on the waitqueue if the request about to be ended is currently
This request was evaluated by Red Hat Product Management for inclusion in a Red
Hat Enterprise Linux maintenance release. Product Management has requested
further review of this request by Red Hat Engineering, for potential
inclusion in a Red Hat Enterprise Linux Update release for currently deployed
products. This request is not yet committed for inclusion in an Update
An advisory has been issued which should help the problem
described in this bug report. This report is therefore being
closed with a resolution of ERRATA. For more information
on therefore solution and/or where to find the updated files,
please follow the link below. You may reopen this bug report
if the solution does not work for you.