BU040625_EW01
 
Potential Dead Lock and KMF in tape cam_changer code

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 Advisory Information
 

RELEASE DATE: 30 March 2005

DESCRIPTION

Update of 30 March 2005:

This Engineering Advisory (EA) is being updated to include an additional correction in cam_changer code. The Early Release Patches (ERPs) identified in the EA now contain two fixes:

  • A potential dead lock condition that manifests as an application hang
  • A potential kernel memory fault (KMF)

The fixes are described below.

A. Potential Dead Lock

A dead lock condition can occur in cam_changer code while a changer application is accessing the media changer. This condition is likely to occur when a previous changer access failed with the error "SCSI device busy," due to a chance that the access lock is not properly released. The dead lock condition manifests as a changer application hang.

B. Potential KMF

A KMF can occur in the cam_changer code if more than one thread attempts to access the changer at the same time. For example, if a robot is moving tapes and another thread opens the same device the panic event is likely to occur. This panic is more likely occur if the customer is running tape backup software that uses multiple changer threads.

When the problem occurs, the customer loses any data written to the tape library before final tape marks have been written. To correct for this condition, the backup process must be reinitiated, which can lengthen the time to complete backups within allocated production time frames.

The following is a typical changer KMF stack trace example:

crash> tf
0 stop_secondary_cpu src/kernel/arch/alpha/cpu.c : 1398
1 panic src/kernel/bsd/subr_prf.c : 1325
2 event_timeout src/kernel/arch/alpha/cpu.c : 2348
3 printf src/kernel/bsd/subr_prf.c : 1008
4 panic src/kernel/bsd/subr_prf.c : 1382
5 trap src/kernel/arch/alpha/trap.c : 2285
6 _XentMM src/kernel/arch/alpha/locore.s : 2237
7 ccmn_record_eei_status3 src/kernel/io/cam/pdrv3_common.c : 4763
8 changer_complete src/kernel/io/cam/cam_changer.c : 7681
9 xpt_callback_thread src/kernel/io/cam/xpt.c : 3357

 

SCOPE

The following product versions are affected:

  • HP Tru64 UNIX 5.1B-2/PK4
  • HP Tru64 UNIX 5.1B PK3
  • HP Tru64 UNIX 5.1A PK6

Affected Audience
Any customer relying on tape changers during backup operations on the affected Tru64 product versions. The risk increases for those customers who are using backup software and/or manual use of robot tape devices where there is a likelihood of more that one I/O thread accessing the device.

 

RESOLUTION
Until the corrections are available in the mainstream release patch kits, HP is releasing the following ERPs publicly for use by any customer.

The ERP kits use dupatch to install and will not install over any installed Customer Specific Patches (CSPs) that have file intersections with the ERPs. Contact your service provider for assistance if the installation of the ERPs is blocked by any of your installed CSPs.

The fixes contained in this ERP kits are scheduled to be available in the following mainstream patch kit:

HP Tru64 UNIX 5.1B-3/PK5

Early Release Patches

The following ERP kits are applicable to any system running HP Tru64 UNIX and HP TruCluster Server software. The ERPs are designed for clustered and non-clustered systems. These patches deliver the following files:

/usr/sys/include/io/cam/cam_changer.h
/sys/BINARY/cam_changer.mod
/sys/BINARY/cam.mod


HP Tru64 UNIX/TruCluster Server 5.1B-2/PK4
ERP Kit Name: T64KIT0025038-V51BB25-E-20050301.tar
ITRC Patch Home: http://www.itrc.hp.com/service/patch/mainPage.do
Kit Location:
http://www.itrc.hp.com/service/patch/patchDetail.do?patchid=T64KIT0025038-V51BB25-E-20050301

HP Tru64 UNIX/TruCluster Server 5.1B-1/PK3
ERP Kit Name: T64KIT0025048-V51BB24-E-20050301.tar
ITRC Patch Home: http://www.itrc.hp.com/service/patch/mainPage.do
Kit Location:
http://www.itrc.hp.com/service/patch/patchDetail.do?patchid=T64KIT0025048-V51BB24-E-20050301

HP Tru64 UNIX/TruCluster Server 5.1A
PREREQUISITE: Tru64 UNIX/TruCluster Server with PK6 installed
ERP Kit Name: T64KIT0025059-V51AB24-E-20050302.tar
ITRC Patch Home: http://www.itrc.hp.com/service/patch/mainPage.do
Kit Location:
http://www.itrc.hp.com/service/patch/patchDetail.do?patchid=T64KIT0025059-V51AB24-E-20050302