SNA Server Access Violation in Function Snaservr!s1prfpda (189053)

SYMPTOMS

The SNA Server service may fail with an access violation after receiving a change number of sessions (CNOS) negotiation error for pending LU 6.2 session requests. If Drwtsn32.exe is configured as the default debugger on the SNA Server system, the Drwtsn32.log file may contain an entry similar to the following when this access violation occurs:

   Application exception occurred:
   App: <path> snaservr.exe (pid=<process ID #>)
   When: <date> @ <time>
   Exception number: c0000005 (access violation)

In addition, the Windows NT Application Event Log may contain an event error message similar to the following if this access violation occurs:

   Event ID: 624
   Source: SNA Server
   Description: Creating dump file <snaroot>\snadump.log for Snaservr.exe

CAUSE

This problem can occur if CNOS negotiation fails and the host returns an error twice with a sequence similar to the following:

The host UNBINDs the SNASVCMG Mode session.

-AND-

The host returns an error to the CNOS GDS variable sent by SNA Server to initiate the CNOS negotiation.

When this occurs, the SNA Server service is removing pending LU 6.2 session requests for a local LU/remote LU/mode from an internal list twice, because there are two different errors being returned. The access violation occurs because the internal list is not being cleaned up properly when an entry is removed from the list, so the second attempt to remove the pending request causes the access violation.

RESOLUTION

SNA Server 3.0

To resolve this problem, obtain the latest service pack for SNA Server version 3.0. For additional information, click the following article number to view the article in the Microsoft Knowledge Base:

184307 How to Obtain the Latest SNA Server Version 3.0 Service Pack

SNA Server 4.0

This problem was corrected in the latest Microsoft SNA Server version 4.0 U.S. Service Pack. For information on obtaining this Service Pack, query on the following word in the Microsoft Knowledge Base (without the spaces):

   S E R V P A C K

STATUS

Microsoft has confirmed that this is a problem in SNA Serverversions 3.0, 3.0 SP1, 3.0 SP2, 3.0 SP3, 4.0, and 4.0 SP1. This problem was first corrected in SNA Server 3.0 Service Pack 4.

MORE INFORMATION

The SNA Server service checks to see whether it has already negotiated CNOS (change number of sessions) for a requested local APPC LU/remote APPC LU/ mode when it receives an open LU 6.2 request for a new LU 6.2 session. If CNOS has not been negotiated for the requested LU/LU/mode, the SNA Server service queues this request by putting it in an internal list created under the requested APPC mode's control block while CNOS negotiation is performed.

After the CNOS negotiation completes successfully or fails, the SNA Server service goes through this internal list and processes all the LU 6.2 requests for the requested local LU/remote LU/mode. As it processes the pending requests, they are removed from the internal list.