Somebody has broken autovacuum's abort path

http://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=jaguar&dt=2010-01-05%2004:00:03
(and the same a couple times before this...)

Core was generated by `postgres: autovacuum worker process   regression                              '.
Program terminated with signal 6, Aborted.
[New process 9209]
#0  0x0091c402 in __kernel_vsyscall ()
#0  0x0091c402 in __kernel_vsyscall ()
#1  0x007a9d80 in raise () from /lib/libc.so.6
#2  0x007ab691 in abort () from /lib/libc.so.6
#3  0x083393be in ExceptionalCondition (   conditionName=0x8498e40 "!(rel->rd_refcnt > 0)",    errorType=0x836d218
"FailedAssertion",fileName=0x8498d55 "relcache.c",    lineNumber=1612) at assert.c:57
 
#4  0x083324c2 in RelationDecrementReferenceCount (rel=0xb5c641e0)   at relcache.c:1612
#5  0x0835b562 in ResourceOwnerReleaseInternal (owner=0x92d1058,    phase=RESOURCE_RELEASE_BEFORE_LOCKS, isCommit=0
'\0',isTopLevel=1 '\001')   at resowner.c:251
 
#6  0x0835b86f in ResourceOwnerRelease (owner=0x92d1058,    phase=RESOURCE_RELEASE_BEFORE_LOCKS, isCommit=0 '\0',
isTopLevel=1'\001')   at resowner.c:185
 
#7  0x080cc5d9 in AbortTransaction () at xact.c:2179
#8  0x080cc7c7 in AbortOutOfAnyTransaction () at xact.c:3676
#9  0x0824063e in do_autovacuum () at autovacuum.c:2259
#10 0x08240b25 in AutoVacWorkerMain (argc=<value optimized out>,    argv=<value optimized out>) at autovacuum.c:1602
#11 0x08240c51 in StartAutoVacWorker () at autovacuum.c:1406
#12 0x0824c0f5 in sigusr1_handler (postgres_signal_arg=10)   at postmaster.c:4307
#13 <signal handler called>
#14 0x0091c402 in __kernel_vsyscall ()
#15 0x0084b1dd in ___newselect_nocancel () from /lib/libc.so.6
#16 0x082486e0 in ServerLoop () at postmaster.c:1364
#17 0x08249d96 in PostmasterMain (argc=6, argv=0x924d918) at postmaster.c:1069
#18 0x081eb080 in main (argc=6, argv=0x0) at main.c:188

I think this can likely be blamed on the HS changes in transaction
abort, since I'm not aware of any other recent changes near here.
        regards, tom lane