OA45240: DATOFF OVERLAYS NUCLEUS CORRUPTION BPX1VRW BPXVNRW ABEND073 ABEND0C1 IN IAXUH OVERLAY OVERLAID

Obtain the fix for this APAR.

APAR status

• Closed as program error.

Error description

• Storage overlays following write of mmap() buffer
  Shortly after migrating to z/OS 2.1, the customer started
  receiving numerous SVC dumps for a variety of ABENDs/symptoms:
  .
  ABEND073
  ABEND0C1 in IAXUH/IRAPACAP (overlay of module IAXUH/IRAPACAP)
  Corruption to pages of Read/Only nucleus
  Page of UCBs overlaid
  .
  The symptoms can really be just about anything, depending upon
  which real frames get inadvertently written to.
     GTF trace records cut from DAT-OFF linkage code showed that
  BPXVNRW was using the 31-bit DAT-OFF linkage to move data, but
  the data was actually backed by 64-bit real frames.  Thus, data
  was being moved between the wrong real frames.
     At z/OS 2.1, we changed our z/OS UNIX dynamic area stack cell
  pool (OcvtJcpcCpid) to be backed by 1MB page frames, which
  results in our 31-bit virtual stack storage being backed by
  64-bit real frames.  Before this change at z/OS 2.1, our stack
  storage was backed by 31-bit real frames.  BPXVNRW was not
  updated at z/OS 2.1 to handle the OMVS buffer (in the dynamic
  area storage) being backed by 64-bit real frames.
     This problem affects users of memory map (mmap) when the
  underlying PFS is NFS Client, TFS, or the XPFS (shared file
  system function-shipping client).
  

Local fix

• N/A
  

Problem summary

• ****************************************************************
  * USERS AFFECTED: All users of z/OS UNIX System Services for   *
  *                 HBB7790 using memory map (mmap) when the     *
  *                 underlying PFS is NFS Client, TFS, or the    *
  *                 XPFS (shared file system function-shipping   *
  *                 client).                                     *
  ****************************************************************
  * PROBLEM DESCRIPTION: On a read, after the PFS reads the      *
  *                      data, what is returned will be          *
  *                      incorrect, being copied from an         *
  *                      incorrect storage location.             *
  *                                                              *
  *                      On a write the data will be written to  *
  *                      an incorrect location prior to calling  *
  *                      the PFS to write it.  This will result  *
  *                      in a storage overlay.  The results      *
  *                      following the overlay are               *
  *                      unpredictable.                          *
  ****************************************************************
  * RECOMMENDATION: Apply ++APAR IA45240 until a PTF is          *
  *                 made available.                              *
  ****************************************************************
  When the PFS does not itself support real addresses passed on
  the v_rdwr call, the service handles it by using an intermediate
  buffer to pass to the PFS, copying the data from / to this
  buffer for read / write respectively.  If the intermediate
  buffer storage real address is above 2GB an incorrect address is
  used.
  
  Thus for a read, the data returned will come from an incorrect
  location, instead of the data read by the PFS.  For a write a
  storage overlay will result when this intermediate buffer is
  written to by the v_rdwr syscall when it copies the data to be
  written to the intermediate buffer.
  
  This is because, when the real address of the intermediate
  buffer is above the 2GB bar, the address used is truncated to a
  31-bit address.
  

Problem conclusion

• The v_rdwr syscall will no longer use DATOFF to move data into
  or out of the intermediate buffer.  Instead it will use an MVCL
  with a real space ALET.
  

Temporary fix

• *********
  * HIPER *
  *********
  

Comments

APAR Information

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

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

  UA74106

Modules/Macros

• BPXJIT   BPXVNRW
  

Fix information

• Fixed component name

  OPENMVS SYS SRV

• Fixed component ID

  5695SCPX1

Applicable component levels

• R790 PSY UA74106

     UP14/07/25 P F407 Ž

Fix is available

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