Server Crash while executing pg_replication_slot_advance (second time)

Hi,

Getting an another server crash against latest sources of v11 while
executing pg_replication_slot_advance second time . This issue is also 
reproducible  with the patch given at <Link>
<https://www.postgresql.org/message-id/CAAJ_b9721pXZST4tGs%2BNPbjRxXF7gmrEomVhTW_Pa2QFD7Lr1A%40mail.gmail.com>

Test-Case scenario-

postgres=#  SELECT * FROM
pg_create_logical_replication_slot('regression_slot1', 'test_decoding',
true);
    slot_name     |    lsn
------------------+-----------
 regression_slot1 | 0/4000258
(1 row)

postgres=# select * from pg_replication_slots;
    slot_name     |    plugin     | slot_type | datoid | database |
temporary | active | active_pid | xmin | catalog_xmin | restart_lsn |
confirmed_flush_lsn
------------------+---------------+-----------+--------+----------+-----------+--------+------------+------+--------------+-------------+---------------------
 regression_slot1 | test_decoding | logical   |  13220 | postgres |
t         | t      |       8756 |      |          557 | 0/4000220   |
0/4000258
(1 row)

postgres=# select pg_switch_wal();
 pg_switch_wal
---------------
 0/4000270
(1 row)

postgres=# select pg_switch_wal();
 pg_switch_wal
---------------
 0/5000000
(1 row)

postgres=# SELECT end_lsn FROM
pg_replication_slot_advance('regression_slot1', '0/5000000');
  end_lsn
-----------
 0/5000000
(1 row)

postgres=# select * from pg_replication_slots;
    slot_name     |    plugin     | slot_type | datoid | database |
temporary | active | active_pid | xmin | catalog_xmin | restart_lsn |
confirmed_flush_lsn
------------------+---------------+-----------+--------+----------+-----------+--------+------------+------+--------------+-------------+---------------------
 regression_slot1 | test_decoding | logical   |  13220 | postgres |
t         | t      |       8756 |      |          557 | 0/4000220   |
0/5000000
(1 row)

postgres=# select pg_switch_wal();
 pg_switch_wal
---------------
 0/5000078
(1 row)

postgres=# select pg_switch_wal();
 pg_switch_wal
---------------
 0/6000000
(1 row)

postgres=# SELECT end_lsn FROM
pg_replication_slot_advance('regression_slot1', '0/6000000');
server closed the connection unexpectedly
    This probably means the server terminated abnormally
    before or while processing the request.
The connection to the server was lost. Attempting reset: Failed.
!> \q

Stack trace -

Core was generated by `postgres: centos postgres [local]
SELECT                      '.
Program terminated with signal 6, Aborted.
#0  0x0000003746e325e5 in raise () from /lib64/libc.so.6
Missing separate debuginfos, use: debuginfo-install
glibc-2.12-1.192.el6.x86_64 keyutils-libs-1.4-5.el6.x86_64
krb5-libs-1.10.3-57.el6.x86_64 libcom_err-1.41.12-22.el6.x86_64
libselinux-2.0.94-7.el6.x86_64 openssl-1.0.1e-48.el6_8.4.x86_64
zlib-1.2.3-29.el6.x86_64
(gdb) bt
#0  0x0000003746e325e5 in raise () from /lib64/libc.so.6
#1  0x0000003746e33dc5 in abort () from /lib64/libc.so.6
#2  0x0000000000a11f8a in ExceptionalCondition (conditionName=0xad5f00
"!(((RecPtr) % 8192 >= (((uintptr_t) ((sizeof(XLogPageHeaderData))) +
((8) - 1)) & ~((uintptr_t) ((8) - 1)))))",
    errorType=0xad5eed "FailedAssertion", fileName=0xad5ee0
"xlogreader.c", lineNumber=243) at assert.c:54
#3  0x000000000055df1d in XLogReadRecord (state=0x2d859c0,
RecPtr=83886080, errormsg=0x7ffd6a4359f8) at xlogreader.c:243
#4  0x00000000008516bc in pg_logical_replication_slot_advance
(startlsn=83886080, moveto=100663296) at slotfuncs.c:370
#5  0x0000000000851a21 in pg_replication_slot_advance
(fcinfo=0x7ffd6a435bb0) at slotfuncs.c:488
#6  0x00000000006defdc in ExecMakeTableFunctionResult
(setexpr=0x2d5e260, econtext=0x2d5df58, argContext=0x2da97f0,
expectedDesc=0x2d5f780, randomAccess=0 '\000') at execSRF.c:231
#7  0x00000000006f1782 in FunctionNext (node=0x2d5de40) at
nodeFunctionscan.c:95
#8  0x00000000006de80d in ExecScanFetch (node=0x2d5de40,
accessMtd=0x6f16cb <FunctionNext>, recheckMtd=0x6f1abd
<FunctionRecheck>) at execScan.c:95
#9  0x00000000006de8ad in ExecScan (node=0x2d5de40, accessMtd=0x6f16cb
<FunctionNext>, recheckMtd=0x6f1abd <FunctionRecheck>) at execScan.c:162
#10 0x00000000006f1b0a in ExecFunctionScan (pstate=0x2d5de40) at
nodeFunctionscan.c:270
#11 0x00000000006dcd66 in ExecProcNodeFirst (node=0x2d5de40) at
execProcnode.c:446
#12 0x00000000006d3c05 in ExecProcNode (node=0x2d5de40) at
../../../src/include/executor/executor.h:246
#13 0x00000000006d6559 in ExecutePlan (estate=0x2d5dc28,
planstate=0x2d5de40, use_parallel_mode=0 '\000', operation=CMD_SELECT,
sendTuples=1 '\001', numberTuples=0,
    direction=ForwardScanDirection, dest=0x2d63628, execute_once=1
'\001') at execMain.c:1721
#14 0x00000000006d41d7 in standard_ExecutorRun (queryDesc=0x2cce878,
direction=ForwardScanDirection, count=0, execute_once=1 '\001') at
execMain.c:361
#15 0x00000000006d3ff3 in ExecutorRun (queryDesc=0x2cce878,
direction=ForwardScanDirection, count=0, execute_once=1 '\001') at
execMain.c:304
#16 0x00000000008afeeb in PortalRunSelect (portal=0x2d0e838, forward=1
'\001', count=0, dest=0x2d63628) at pquery.c:932
#17 0x00000000008afb79 in PortalRun (portal=0x2d0e838,
count=9223372036854775807, isTopLevel=1 '\001', run_once=1 '\001',
dest=0x2d63628, altdest=0x2d63628,
    completionTag=0x7ffd6a436480 "") at pquery.c:773
#18 0x00000000008a9ba0 in exec_simple_query (query_string=0x2ca9438
"SELECT end_lsn FROM pg_replication_slot_advance('regression_slot1',
'0/6000000');") at postgres.c:1120
#19 0x00000000008ade34 in PostgresMain (argc=1, argv=0x2cd4ec0,
dbname=0x2cd4d20 "postgres", username=0x2ca5f58 "centos") at postgres.c:4144
#20 0x000000000080d11a in BackendRun (port=0x2cccd00) at postmaster.c:4412
#21 0x000000000080c88e in BackendStartup (port=0x2cccd00) at
postmaster.c:4084
#22 0x0000000000808cbb in ServerLoop () at postmaster.c:1757
#23 0x0000000000808379 in PostmasterMain (argc=3, argv=0x2ca3eb0) at
postmaster.c:1365
#24 0x000000000073d3d0 in main (argc=3, argv=0x2ca3eb0) at main.c:228
(gdb)

--
regards,tushar
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