BUG #5952: SetRWConflict assertion failure

The following bug has been logged online:

Bug reference: 5952
Logged by: YAMAMOTO Takashi
Email address: yamt(at)mwd(dot)biglobe(dot)ne(dot)jp
PostgreSQL version: 9.1devel
Operating system: NetBSD
Description: SetRWConflict assertion failure
Details:

i got the following assertion failure with
71ac48fd9cebd3d2a873635a04df64096c981f73.

(with this patch applied, if it matters:
http://archives.postgresql.org/pgsql-hackers/2011-03/msg01180.php)

SerializableXactHashLock relocking in CheckTargetForConflictsIn() seems
racy to me.

(gdb) bt
#0 0xbbba4cc7 in _lwp_kill () from /usr/lib/libc.so.12
#1 0xbbba4c85 in raise (s=6) at /siro/nbsd/src/lib/libc/gen/raise.c:48
#2 0xbbba445a in abort () at /siro/nbsd/src/lib/libc/stdlib/abort.c:74
#3 0x083df0d8 in ExceptionalCondition (
conditionName=0x854f370 "!(!RWConflictExists(reader, writer))",
errorType=0x854f320 "FailedAssertion", fileName=0x854f314
"predicate.c",
lineNumber=565) at assert.c:57
#4 0x082e9a1c in SetRWConflict (reader=0xbb7cce1c, writer=0xbb7c9720)
at predicate.c:565
#5 0x082ef299 in FlagRWConflict (reader=0xbb7cce1c, writer=0xbb7c9720)
at predicate.c:3870
#6 0x082eeeeb in CheckTargetForConflictsIn (targettag=0xbfbfda28)
at predicate.c:3774
#7 0x082ef1cc in CheckForSerializableConflictIn (relation=0xb941a450,
tuple=0x0, buffer=1901) at predicate.c:3841
#8 0x080bb5cc in _bt_doinsert (rel=0xb941a450, itup=0xb9484684,
checkUnique=UNIQUE_CHECK_YES, heapRel=0xbb9ebfec) at nbtinsert.c:185
#9 0x080c33ee in btinsert (fcinfo=0xbfbfdaf0) at nbtree.c:262
#10 0x083e6b55 in FunctionCall6 (flinfo=0xb946a01c, arg1=3108086864,
arg2=3217022352, arg3=3217022320, arg4=3108521372, arg5=3147743212,
arg6=1)
at fmgr.c:1488
#11 0x080b95a7 in index_insert (indexRelation=0xb941a450,
values=0xbfbfdd90,
isnull=0xbfbfdd70 "", heap_t_ctid=0xb948459c, heapRelation=0xbb9ebfec,
checkUnique=UNIQUE_CHECK_YES) at indexam.c:205
#12 0x081f9a85 in ExecInsertIndexTuples (slot=0xb9483be0,
tupleid=0xb948459c,
estate=0xb944501c) at execUtils.c:1084
#13 0x082096df in ExecUpdate (tupleid=0xbfbfdef6, oldtuple=0x0,
slot=0xb9483be0, planSlot=0xb9446cc4, epqstate=0xb94455e0,
estate=0xb944501c, canSetTag=1 '\001') at nodeModifyTable.c:627
#14 0x08209ba3 in ExecModifyTable (node=0xb9445588) at
nodeModifyTable.c:838
#15 0x081edc31 in ExecProcNode (node=0xb9445588) at execProcnode.c:371
#16 0x081ebcc4 in ExecutePlan (estate=0xb944501c, planstate=0xb9445588,
operation=CMD_UPDATE, sendTuples=0 '\0', numberTuples=0,
direction=ForwardScanDirection, dest=0x8592fa4) at execMain.c:1385
#17 0x081ea5c9 in standard_ExecutorRun (queryDesc=0xb9464cfc,
direction=ForwardScanDirection, count=0) at execMain.c:311
#18 0x081ea466 in ExecutorRun (queryDesc=0xb9464cfc,
direction=ForwardScanDirection, count=0) at execMain.c:259
#19 0x082faff9 in ProcessQuery (plan=0xb946b04c,
sourceText=0xb9464c1c "UPDATE file SET mtime = current_timestamp, ctime
= current_timestamp, rev = rev + 1 WHERE fileid = $1", params=0xb9464cbc,
dest=0x8592fa4, completionTag=0xbfbfe1e0 "") at pquery.c:187
#20 0x082fc56b in PortalRunMulti (portal=0xbb9b601c, isTopLevel=1 '\001',
dest=0x8592fa4, altdest=0x8592fa4, completionTag=0xbfbfe1e0 "")
at pquery.c:1276
#21 0x082fbd32 in PortalRun (portal=0xbb9b601c, count=2147483647,
isTopLevel=1 '\001', dest=0xbb91c428, altdest=0xbb91c428,
completionTag=0xbfbfe1e0 "") at pquery.c:813
#22 0x082f7afd in exec_execute_message (portal_name=0xbb91c01c "",
max_rows=2147483647) at postgres.c:1963
#23 0x082fa43d in PostgresMain (argc=2, argv=0xbb919618,
username=0xbb91956c "takashi") at postgres.c:3965
#24 0x082aae0b in BackendRun (port=0xbb9510f0) at postmaster.c:3590
#25 0x082aa4cf in BackendStartup (port=0xbb9510f0) at postmaster.c:3275
#26 0x082a774f in ServerLoop () at postmaster.c:1449
#27 0x082a6efe in PostmasterMain (argc=3, argv=0xbfbfe590) at
postmaster.c:1110
#28 0x08227740 in main (argc=3, argv=0xbfbfe590) at main.c:199
(gdb) fr 4
#4 0x082e9a1c in SetRWConflict (reader=0xbb7cce1c, writer=0xbb7c9720)
at predicate.c:565
565 Assert(!RWConflictExists(reader, writer));
(gdb) p *reader
$1 = {vxid = {backendId = 3, localTransactionId = 658423},
commitSeqNo = 18446744073709551615, SeqNo = {
earliestOutConflictCommit = 3617761, lastCommitBeforeSnapshot =
3617761},
outConflicts = {prev = 0xbb7da7e0, next = 0xbb7da7e0}, inConflicts = {
prev = 0xbb7cce3c, next = 0xbb7cce3c}, predicateLocks = {
prev = 0xbb858950, next = 0xbb84e090}, finishedLink = {prev = 0x0,
next = 0x0}, possibleUnsafeConflicts = {prev = 0xbb7cce54,
next = 0xbb7cce54}, topXid = 1267267, finishedBefore = 0, xmin =
1267266,
flags = 0, pid = 21551}
(gdb) p *writer
$2 = {vxid = {backendId = 4, localTransactionId = 943664},
commitSeqNo = 18446744073709551615, SeqNo = {
earliestOutConflictCommit = 3617761, lastCommitBeforeSnapshot =
3617761},
outConflicts = {prev = 0xbb7c9738, next = 0xbb7c9738}, inConflicts = {
prev = 0xbb7da7e8, next = 0xbb7da7e8}, predicateLocks = {
prev = 0xbb861fe0, next = 0xbb861fe0}, finishedLink = {prev = 0x0,
next = 0x0}, possibleUnsafeConflicts = {prev = 0xbb7c9758,
next = 0xbb7c9758}, topXid = 1267266, finishedBefore = 0, xmin =
1267266,
flags = 16, pid = 9331}
(gdb)