A fix is available
APAR status
Closed as unreproducible in next release.
Error description
Infinite loop in module ISTTSCDX issuing XCF ISGMSGCF DISCARD requests to purge outstanding messages. Eventually SQA is becomes exhausted leading to ABENDS878.
Local fix
Problem summary
**************************************************************** * USERS AFFECTED: All using XCF connections. * **************************************************************** * PROBLEM DESCRIPTION: Infinite loop occurs in module * * ISTTSCDX after an XCF INOP. * **************************************************************** * RECOMMENDATION: * **************************************************************** The problem is summarized as follows: 1) An XCF link is established between two hosts within a sysplex. 2) At some point, an XCF disconnect is received on one of the hosts. Module ISTTSCBX takes down the XCF link by INOPing the connection with a reason code of 1. 3) Meanwhile, the XCF connection still has inbound message to process. Module ISTTSCDX is in control processing within a loop which queries XCF, via the IXCMSGCP REQUEST(QUERYMSG) interface, to locate any inbound messages for this connection. 4) As a result of the query, VTAM receives back 74 tokens from the query output. There is also a flag indicating there are more messages to receive from XCF. 5) Since the XCF link is coming down, VTAM issues a IXCMSGCP REQUEST(DISCARDMSG) to discard each inbound message. Each DISCARDMSG request allocates an XCF SISM control block and schedules an SRB to drive the XCF MSGEXIT. When the MSGEXIT SRB dispatches, XCF will discard the specific message. 6) After the first set of 74 messages are processed, module ISTTSCDX continues to query XCF for more messages. After do so, it appears the same exact entries are being returned. Module ISTTSCDX continues to issue DISCARDMSG requests, which in turn allocates more SQA storage. 7) Examination of the dump taken at the time of the error showed hundreds of thousands of SISM control blocks queued to VTAM for processing. Further analysis revealed the scheduled MSGEXIT SRBs were not getting dispatched. It appears VTAM's main task was synchronously issuing an SVC purge (ISTTSCLR) for an unrelated channel (CUA). 8) Module ISTTSCDX continues to issue XCF QUERYMSG and DISCARDMSG requests until SQA becomes exhausted an an ABEND878 occurs.
Problem conclusion
Temporary fix
********* * HIPER * *********
Comments
ISTAPNVT - Has been changed to define a new bit, APN_Sched_IMPAB, which means the Wake Up PAB should TPSCHEDule the XCF Inbound Message PAB. ISTTSCDX - Has been changed to recognize if the first message returned by XCF from a QUERYMSG function is the same one returned from the prior QUERYMSG. If this occurs, module ISTTSCDX will set new flag, APN_Sched_IMPAB, and immediately exit the loop. This allows other processes, like the XCF MSGEXIT SRBs to run. ISTTSCWU - Has been changed to schedule the XCF Inbound Message PAB if the APN_Sched_IMPAB bit is on. ISTTSCMA - Included for maintenance purposes only.
APAR Information
APAR number
OA38811
Reported component name
VTAM V4 MVS/ESA
Reported component ID
569511701
Reported release
1D0
Status
CLOSED UR1
PE
NoPE
HIPER
YesHIPER
Special Attention
NoSpecatt / Xsystem
Submitted date
2012-02-15
Closed date
2012-03-06
Last modified date
2012-05-02
APAR is sysrouted FROM one or more of the following:
APAR is sysrouted TO one or more of the following:
UA64486 UA64487 UA64488
Modules/Macros
ISTAPNVT ISTTSCDX ISTTSCMA ISTTSCWU
Fix information
Fixed component name
VTAM V4 MVS/ESA
Fixed component ID
569511701
Applicable component levels
R1B0 PSY UA64486
UP12/04/17 P F204
R1C0 PSY UA64487
UP12/04/17 P F204
R1D0 PSY UA64488
UP12/04/17 P F204
Fix is available
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Document Information
Modified date:
02 May 2012