Still something fishy in the fastpath lock stuff

Buildfarm member prairiedog crashed on today's HEAD with this:

TRAP: FailedAssertion("!(FastPathStrongRelationLocks->count[fasthashcode] > 0)", File: "lock.c", Line: 1240)

I have the core file, and gdb says:

#0  0x90047dac in kill ()
#1  0x9012d7b4 in abort ()
#2  0x003b1c38 in ExceptionalCondition (conditionName=0x0, errorType=0x25 "", fileName=0x2 "", lineNumber=109) at
assert.c:54
#3  0x002960bc in RemoveLocalLock (locallock=0x280b414) at lock.c:1240
#4  0x002968a4 in LockReleaseAll (lockmethodid=1, allLocks=0 '\0') at lock.c:2087
#5  0x00299550 in ProcReleaseLocks (isCommit=1 '\001') at proc.c:752
#6  0x003de2d4 in ResourceOwnerReleaseInternal (owner=0x2802184, phase=RESOURCE_RELEASE_LOCKS, isCommit=1 '\001',
isTopLevel=1'\001') at resowner.c:307
 
#7  0x003de71c in ResourceOwnerRelease (owner=0x2802184, phase=RESOURCE_RELEASE_LOCKS, isCommit=1 '\001', isTopLevel=1
'\001')at resowner.c:212
 
#8  0x00083b7c in CommitTransaction () at xact.c:1998
#9  0x00083ea4 in CommitTransactionCommand () at xact.c:2713
#10 0x002ab9b4 in finish_xact_command () at postgres.c:2408
#11 0x002af2b0 in exec_simple_query (query_string=0x2807e1c "CREATE TABLE t3 (name TEXT, n INTEGER);") at
postgres.c:1076
#12 0x002b08bc in PostgresMain (argc=41975324, argv=0xbfffdd3c, dbname=0x2800b6c "regression", username=0x51 "") at
postgres.c:4004
#13 0x0023d5bc in ServerLoop () at postmaster.c:4089
#14 0x0023f11c in PostmasterMain (argc=6, argv=0x46d9d0) at postmaster.c:1222
#15 0x001bb89c in main (argc=6, argv=0x2100710) at main.c:203

Since this machine has only been running the buildfarm for a week,
I rather imagine we will see more of these.  Thoughts?

(This is a PPC machine, but only a single processor, so it's hard
to see how memory ordering issues might enter into it ...)
        regards, tom lane