BUG #17116: Assert failed in SerialSetActiveSerXmin() on commit of parallelized serializable transaction

The following bug has been logged on the website:

Bug reference:      17116
Logged by:          Alexander Lakhin
Email address:      exclusion@gmail.com
PostgreSQL version: 13.3
Operating system:   Ubuntu 20.04
Description:

The isolation test "serializable-parallel-2" modified as follows:
# Exercise the case where a read-only serializable transaction has
# SXACT_FLAG_RO_SAFE set in a parallel query.

setup
{
    CREATE TABLE foo AS SELECT generate_series(1, 10)::int a;
    ALTER TABLE foo SET (parallel_workers = 2);
}

teardown
{
    DROP TABLE foo;
}

session s1
setup         { BEGIN TRANSACTION ISOLATION LEVEL SERIALIZABLE; }
step s1r    { SELECT * FROM foo; }
step s1c    { COMMIT; }

session s2
setup        {
              BEGIN TRANSACTION ISOLATION LEVEL SERIALIZABLE READ ONLY;
              SET parallel_setup_cost = 0;
              SET parallel_tuple_cost = 0;
            }
step s2r1    { SELECT * FROM foo; }
step s2r2    { SELECT * FROM foo; }
step s2c    { COMMIT; }

session s3
setup         { BEGIN TRANSACTION ISOLATION LEVEL SERIALIZABLE; }
step s3r    { SELECT * FROM foo; }
step s3c    { COMMIT; }

session s4
setup        {
              BEGIN TRANSACTION ISOLATION LEVEL SERIALIZABLE READ ONLY;
              SET parallel_setup_cost = 0;
              SET parallel_tuple_cost = 0;
            }
step s4r1    { SELECT * FROM foo; }
step s4r2    { SELECT * FROM foo; }
step s4c    { COMMIT; }

permutation s1r s3r s2r1 s4r1 s1c s2r2 s3c s4r2 s4c s2c

leads to a failed assertion with the following stacktrace:
Core was generated by `postgres: law isolation_regression [local] COMMIT
                        '.
Program terminated with signal SIGABRT, Aborted.
#0  __GI_raise (sig=sig@entry=6) at ../sysdeps/unix/sysv/linux/raise.c:50
50      ../sysdeps/unix/sysv/linux/raise.c: No such file or directory.
(gdb) bt
#0  __GI_raise (sig=sig@entry=6) at ../sysdeps/unix/sysv/linux/raise.c:50
#1  0x00007f21de1dd859 in __GI_abort () at abort.c:79
#2  0x0000555e1740b1ac in ExceptionalCondition (
    conditionName=conditionName@entry=0x555e17581ce8
"!TransactionIdIsValid(serialControl->tailXid) || TransactionIdFollows(xid,
serialControl->tailXid)", errorType=errorType@entry=0x555e17466028
"FailedAssertion", 
    fileName=fileName@entry=0x555e17581789 "predicate.c",
lineNumber=lineNumber@entry=1056) at assert.c:67
#3  0x0000555e172d3c5c in SerialSetActiveSerXmin (xid=6187) at
predicate.c:1056
#4  0x0000555e172d3ecf in SetNewSxactGlobalXmin () at predicate.c:3309
#5  0x0000555e172d811c in ReleasePredicateLocks (isCommit=false,
isCommit@entry=true, 
    isReadOnlySafe=isReadOnlySafe@entry=false) at predicate.c:3697
#6  0x0000555e1743fbb0 in ResourceOwnerReleaseInternal (owner=<optimized
out>, 
    phase=phase@entry=RESOURCE_RELEASE_LOCKS, isCommit=isCommit@entry=true,
isTopLevel=isTopLevel@entry=true)
    at resowner.c:569
#7  0x0000555e17440166 in ResourceOwnerRelease (owner=<optimized out>,
phase=phase@entry=RESOURCE_RELEASE_LOCKS, 
    isCommit=isCommit@entry=true, isTopLevel=isTopLevel@entry=true) at
resowner.c:484
#8  0x0000555e1700a156 in CommitTransaction () at xact.c:2227
#9  0x0000555e1700af28 in CommitTransactionCommand () at xact.c:2974
#10 0x0000555e172e319d in finish_xact_command () at postgres.c:2662
#11 0x0000555e172e5972 in exec_simple_query
(query_string=query_string@entry=0x555e18e17350 "COMMIT;")
    at postgres.c:1264
#12 0x0000555e172e7b06 in PostgresMain (argc=<optimized out>,
argv=argv@entry=0x555e18e42ad8, dbname=<optimized out>, 
    username=<optimized out>) at postgres.c:4339
#13 0x0000555e17253165 in BackendRun (port=port@entry=0x555e18e3bb10) at
postmaster.c:4526
#14 0x0000555e172562c0 in BackendStartup (port=port@entry=0x555e18e3bb10) at
postmaster.c:4210
#15 0x0000555e17256507 in ServerLoop () at postmaster.c:1739
#16 0x0000555e17257a30 in PostmasterMain (argc=8, argv=<optimized out>) at
postmaster.c:1412
#17 0x0000555e171a0a4f in main (argc=8, argv=0x555e18e119e0) at main.c:210

(Discovered by running multiple installcheck-world's in parallel.)
Reproduced on REL_12_STABLE..master. It looks like the offending commit is
47a338cf.