Date: Mon, 22 Nov 2004 19:33:51 +0100 From: Georg Altmann <galtmann@las-cad.com> To: freebsd-questions@freebsd.org Subject: semaphore problem with Bakbone's Netvault on FreeBSD 4.10 Message-ID: <C79517C1DAEEB0C790F8D4E7@[192.168.98.23]>
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Hi all, I have a problem running the backup software Netvault from Bakbone (http://www.bakbone.com) under FreeBSD 4.10. We are using Netvault to make backups of two servers and several workstations in our network. Backups are first staged to disk and later transferred to an ADIC FastStor 2 (LTO 1) library. The problem occurs when the backup is transferred from disk to tape and if the backup job spans multiple tapes (not virtual media!): Netvault recognizes the end-of-media, loads a new media for the job and then hangs endlessly trying to write to the new media. Bakbone claims, that this is a problem with SysV shared memory and semaphores in FreeBSD (and therefore not their software). Their support also sent me a patch for Netvault (unfortunately not a binary one, so I cannot test it) which is allegedly known to work around the problem. I attached it below. Note the added "#if defined(PLATFORM_FREEBSD)" bits in the code. To my understanding, the patched code polls the semaphore instead of waiting for it. Please also note, that I configured Netvault to use network sockets instead of shared mem for the transfer and the problem persists (I did this by only selecting "TCP Data Transfer" in the configure device tab for both the tape and the virtual library and by adding [Data Channels]\nForce Sockets=TRUE to configure.cfg as proposed by Bakbone support, for anyone familiar with netvault). So I assume, the problem is really only related to semaphores and not at all to shared memory(?). I hope that someone can guess from the code if this really leads to a deadlock because of a FreeBSD bug in SysV sempaphore handling. I have already skimmed FreeBSD PRs for semaphore bugs, but no post really seemed related to this specific problem (see http://www.freebsd.org/cgi/query-pr-summary.cgi?category=&severity=&priority=&class=&state=&sort=none&text=semaphore&responsible=&multitext=&originator=&closedtoo=on&release=). So, maybe somebody is able to make clear whether I should urge Bakbone to fix their buggy software or look for a patch for the FreeBSD kernel and/or libraries. Some info on the server: $ uname -a FreeBSD asterix.las-cad.local 4.10-RELEASE-p3 FreeBSD 4.10-RELEASE-p3 #0: Sat Sep 25 17:05:29 CEST 2004 root@asterix.las-cad.local:/usr/obj/usr/src/sys/ASTERIX i386 Netvault Version 7.11 Build 10 Release R2004AUG19-CHIEF Hardware: AMD Athlon @ 1100 MHz, 768 MB RAM tape library: ahc0: <Adaptec 29160 Ultra160 SCSI adapter> port 0xbc00-0xbcff mem 0xdfffb000-0xdfffbfff irq 5 at device 12.0 on pci0 sa0 at ahc0 bus 0 target 5 lun 0 sa0: <HP Ultrium 1-SCSI E33A> Removable Sequential Access SCSI-3 device sa0: 80.000MB/s transfers (40.000MHz, offset 15, 16bit) pass0 at ahc0 bus 0 target 0 lun 0 pass0: <ADIC FastStor 2 A12r> Removable Changer SCSI-2 device pass0: 3.300MB/s transfers staging disk: ad4: 114473MB <ST3120022A> [232581/16/63] at ata2-master UDMA100 connected to atapci1: <HighPoint HPT370 ATA100 controller> port 0xc800-0xc8ff,0xcc00-0xcc03,0xd000-0xd007,0xd400-0xd403,0xd800-0xd807 irq 10 at device 10.0 on pci0 ata2: at 0xd800 on atapci1 Thank you! Best regards, Georg Altmann -- >-------------------<>-----------------------------< > Georg Altmann <> Phone +49 (0)89 17809328 < > LAS-CAD GmbH <> Fax +49 (0)89 172594 < > Brunhildenstr. 9 <> e-mail galtmann@las-cad.com < > D-80639 Munich <> backup george@george-net.de < > Germany <> http://www.las-cad.com < >-------------------<>-----------------------------< code: /* ** Wait on a semaphore, i.e., wait for a resource to become available. */ INTERNAL DataResultE DataSemaphoreWait ( DataChannelShmemQualifierO oShmemInfo, int iSemNum, BooleanT *pbBlocked, long *plElapse ) { DataResultE tResult = DataFailure; struct sembuf sOperation; sOperation.sem_num = iSemNum; sOperation.sem_op = -1; /* Decrement semaphore by 1 when it's ready */ sOperation.sem_flg = IPC_NOWAIT; if (0 == semop(oShmemInfo->lSemId, &sOperation, 1)) { TRACE((108, 0, LIBVERBOSE, "Decrement semaphore %d", iSemNum)); if(0 != (*oShmemInfo->pllEomFlag)) { TRACE((173,0,NORMAL,"Got a EOM flag")); tResult = DataEom; } else { tResult = DataSuccess; } } else { long lMyError = errno; #if defined(PLATFORM_FREEBSD) BooleanT bDone = FALSE; while(EAGAIN == lMyError && FALSE == bDone) #else if(EAGAIN == lMyError) #endif /* Not PLATFORM_FREEBSD */ { #if defined(PLATFORM_FREEBSD) sOperation.sem_flg = IPC_NOWAIT; #else sOperation.sem_flg = 0; #endif /* Not PLATFORM_FREEBSD */ if(NULL != plElapse) { int64 llStart = TimeNowAsInt64(); *pbBlocked = TRUE; if (0 == semop(oShmemInfo->lSemId, &sOperation, 1)) { TRACE((109, 0, LIBVERBOSE, "Decrement semaphore %d, after wait", iSemNum)); if(0 != (*oShmemInfo->pllEomFlag)) { TRACE((174,0,NORMAL,"Got a EOM flag")); #if defined(PLATFORM_FREEBSD) tResult = DataEom; #endif /* PLATFORM_FREEBSD */ bDone = TRUE; } else { tResult = DataSuccess; #if defined(PLATFORM_FREEBSD) bDone = TRUE; #endif /* PLATFORM_FREEBSD */ } } else { lMyError = errno; } *plElapse += TimeNowAsInt64() - llStart; } else { if (0 == semop(oShmemInfo->lSemId, &sOperation, 1)) { TRACE((110, 0, LIBVERBOSE, "Decrement semaphore %d, after wait", iSemNum)); if(0 != (*oShmemInfo->pllEomFlag)) { TRACE((176, 0, NORMAL, "Got a EOM flag")); tResult = DataEom; #if defined(PLATFORM_FREEBSD) bDone = TRUE; #endif /* PLATFORM_FREEBSD */ } else { tResult = DataSuccess; #if defined(PLATFORM_FREEBSD) bDone = TRUE; #endif /* PLATFORM_FREEBSD */ } } else { lMyError = errno; } } } if(DataSuccess != tResult && DataEom != tResult) { if (EINTR != lMyError) { TRACE((2, lMyError, LIBNORMAL, "wait on semaphore %ld failed: %s", iSemNum, SysErrorString(lMyError))); } else { tResult = DataInterrupted; } } } return tResult; } #endif
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