[sqlsmith] Failed assertion in _hash_kill_items/MarkBufferDirtyHint

Hi,

testing with master as of cf366e97ff, sqlsmith occasionally triggers the
following assertion:

TRAP: FailedAssertion("!(LWLockHeldByMe(((LWLock*) (&(bufHdr)->content_lock))))", File: "bufmgr.c", Line: 3397)

Backtraces always look like the one below. It is reproducible on a
cluster once it happens. I could provide a tarball if needed.

regards,
Andreas

#2 0x00000000008324b1 in ExceptionalCondition (conditionName=conditionName(at)entry=0x9e4e28 "!(LWLockHeldByMe(((LWLock*) (&(bufHdr)->content_lock))))", errorType=errorType(at)entry=0x87b03d "FailedAssertion", fileName=fileName(at)entry=0x9e5856 "bufmgr.c", lineNumber=lineNumber(at)entry=3397) at assert.c:54
#3 0x0000000000706971 in MarkBufferDirtyHint (buffer=2844, buffer_std=buffer_std(at)entry=1 '\001') at bufmgr.c:3397
#4 0x00000000004b3ecd in _hash_kill_items (scan=scan(at)entry=0x66dcf70) at hashutil.c:514
#5 0x00000000004a9c1b in hashendscan (scan=0x66dcf70) at hash.c:512
#6 0x00000000004cf17a in index_endscan (scan=0x66dcf70) at indexam.c:353
#7 0x000000000061fa51 in ExecEndIndexScan (node=0x3093f30) at nodeIndexscan.c:852
#8 0x0000000000608e59 in ExecEndNode (node=<optimized out>) at execProcnode.c:715
#9 0x00000000006045b8 in ExecEndPlan (estate=0x3064000, planstate=<optimized out>) at execMain.c:1540
#10 standard_ExecutorEnd (queryDesc=0x30cb880) at execMain.c:487
#11 0x00000000005c87b0 in PortalCleanup (portal=0x1a60060) at portalcmds.c:302
#12 0x000000000085cbb3 in PortalDrop (portal=0x1a60060, isTopCommit=<optimized out>) at portalmem.c:489
#13 0x0000000000736ed2 in exec_simple_query (query_string=0x315b7a0 "...") at postgres.c:1111
#14 0x0000000000738b51 in PostgresMain (argc=<optimized out>, argv=argv(at)entry=0x1a6c6c8, dbname=<optimized out>, username=<optimized out>) at postgres.c:4071
#15 0x0000000000475fef in BackendRun (port=0x1a65b90) at postmaster.c:4317
#16 BackendStartup (port=0x1a65b90) at postmaster.c:3989
#17 ServerLoop () at postmaster.c:1729
#18 0x00000000006c8662 in PostmasterMain (argc=argc(at)entry=4, argv=argv(at)entry=0x1a3f540) at postmaster.c:1337
#19 0x000000000047729d in main (argc=4, argv=0x1a3f540) at main.c:228