VM66319: PEVM66301 SYSTEM HANG WITH EDEVS OR PAGING63 PARM

Obtain the fix for this APAR.

APAR status

• Closed as program error.

Error description

• z/VM code for managing paging and spool I/O is exposed to a
  deadlock in certain configurations.
  Using certain paging configurations or MAPMDISK with EDEVs,
  the z/VM control program (CP) storage management code may
  acquire locks in an interdependent fashion and cause a system
  hang.  This only affects users paging to SCSI configurations,
  using SCSI for spool space, using SCSI with MAPMDISK for
  guests, or those using the legacy PAGING63 IPL parameter.  The
  problem is timing-related so chances of achieving the
  required conditions increase with paging rates.
  Other keywords: PPIBK EXPBK
  

Local fix

Problem summary

• ****************************************************************
  * USERS AFFECTED: z/VM users paging to EDEVs, using EDEVs for  *
  *                 spool space, having guests using MAPMDISK    *
  *                 with EDEVs, or using the PAGING63 IPL        *
  *                 parameter. This could also appear on second  *
  *                 level z/VM systems where first level VDISK   *
  *                 is brought up and used as an emulated FBA    *
  *                 device for paging, spool, or MAPMDISK.       *
  ****************************************************************
  * PROBLEM DESCRIPTION:                                         *
  ****************************************************************
  * RECOMMENDATION: APPLY PTF                                    *
  ****************************************************************
  After applying APAR VM66301, users with EDEVs for paging or
  spool, or EDEVs for guest MAPMDISK usage, or those using the
  PAGING63 IPL parameter with EDEVs or ECKD DASD may
  experience a system hang. VM66301 introduced a new field,
  PPISVGIU, in the PPIBK (the remapping/re-labeling of SVGBK
  and SVGWRK fields) to allow HCPPAG to indicate its continued
  use of the save area.  However, it introduced a lock hierarchy
  issue with the EXPLCKFG in the EXPBK (the exposure control
  block that contains information about a CP paging or spool
  volume).  The EXPBK is used in paging or spool operations to
  EDEVs, MAPMDISK operations to EDEVs, and in 6.3 and older
  code for ECKD and EDEV paging and spool.  With higher I/O
  rates, it is more likely that the lock hierarchy violation
  will result in a deadlock between PPISVGIU and EXPLCKFG.
  
  Users with ECKD for paging and spool space who are not
  using the PAGING63 IPL parameter are not exposed, as new code
  put in with z/VM 6.4 uses a different control block and a
  different locking mechanism for this type of I/O.
  
  To determine if the PAGING63 IPL parameter is currently active,
  issue QUERY PAGING.  If PAGING_ALIAS and PAGING_HPF indicate
  Unavailable, then PAGING63 is active.
  

Problem conclusion

• APAR VM66301 is in error.
  
  Previously, HCPPAH acquired PPISVGIU and stacked a return to
  the original HCPPAG caller while already holding EXPLCKFG.
  
  HCPPAH has been updated to now stack a goto to HCPPAGRT, a new
  entry point.  HCPPAGRT runs without a hold of EXPLCKFG and
  acquires PPISVGIU prior to returning to the original HCPPAG
  caller.  Moving the code that acquires PPISVGIU and returns to
  the original caller outside of the EXPLCKFG lock hold avoids
  the lock hierarchy violation and possibility of a deadlock.
  

Temporary fix

• *********
  * HIPER *
  *********
  FOR RELEASE VM/ESACP/ESAR710 :
  PREREQ: VM66301
  CO-REQ: NONE
  IF-REQ: NONE
  

Comments

APAR Information

• APAR is sysrouted FROM one or more of the following:

• APAR is sysrouted TO one or more of the following:

  UM35530

Modules/Macros

• CPLOAD   HCPMDLAT HCPPAG   HCPPAH
  

Fix information

• Fixed component name

  VM CP

• Fixed component ID

  568411202

Applicable component levels

• R710 PSY UM35530

     UP19/09/20 P 2001 ­

Fix is available

• Select the PTF appropriate for your component level. You will be required to sign in. Distribution on physical media is not available in all countries.