Crash in new pgstats code

mylodon just showed a new-to-me failure mode [1]:

Core was generated by `postgres: cascade: startup recovering 000000010000000000000002 '.
Program terminated with signal SIGABRT, Aborted.
#0 __GI_raise (sig=sig(at)entry=6) at ../sysdeps/unix/sysv/linux/raise.c:49
49 ../sysdeps/unix/sysv/linux/raise.c: No such file or directory.
#0 __GI_raise (sig=sig(at)entry=6) at ../sysdeps/unix/sysv/linux/raise.c:49
#1 0x00007f8b8db2d546 in __GI_abort () at abort.c:79
#2 0x000000000098a4dc in ExceptionalCondition (conditionName=<optimized out>, errorType=0x9e8061 "FailedAssertion", fileName=0xaf811f "/mnt/resource/bf/build/mylodon/HEAD/pgsql.build/../pgsql/src/backend/lib/dshash.c", lineNumber=lineNumber(at)entry=744) at /mnt/resource/bf/build/mylodon/HEAD/pgsql.build/../pgsql/src/backend/utils/error/assert.c:69
#3 0x00000000006dbe65 in dshash_delete_current (status=status(at)entry=0x7fffec732dc8) at /mnt/resource/bf/build/mylodon/HEAD/pgsql.build/../pgsql/src/backend/lib/dshash.c:744
#4 0x000000000085f911 in pgstat_free_entry (shent=0x7f8b8b0fc320, hstat=0x7fffec732dc8) at /mnt/resource/bf/build/mylodon/HEAD/pgsql.build/../pgsql/src/backend/utils/activity/pgstat_shmem.c:741
#5 pgstat_drop_entry_internal (shent=0x7f8b8b0fc320, hstat=hstat(at)entry=0x7fffec732dc8) at /mnt/resource/bf/build/mylodon/HEAD/pgsql.build/../pgsql/src/backend/utils/activity/pgstat_shmem.c:773
#6 0x000000000085fa2e in pgstat_drop_all_entries () at /mnt/resource/bf/build/mylodon/HEAD/pgsql.build/../pgsql/src/backend/utils/activity/pgstat_shmem.c:887
#7 0x0000000000859301 in pgstat_reset_after_failure () at /mnt/resource/bf/build/mylodon/HEAD/pgsql.build/../pgsql/src/backend/utils/activity/pgstat.c:1631
#8 pgstat_discard_stats () at /mnt/resource/bf/build/mylodon/HEAD/pgsql.build/../pgsql/src/backend/utils/activity/pgstat.c:435
#9 0x0000000000555ae0 in StartupXLOG () at /mnt/resource/bf/build/mylodon/HEAD/pgsql.build/../pgsql/src/backend/access/transam/xlog.c:5127
#10 0x00000000007a8ece in StartupProcessMain () at /mnt/resource/bf/build/mylodon/HEAD/pgsql.build/../pgsql/src/backend/postmaster/startup.c:267
#11 0x000000000079f44e in AuxiliaryProcessMain (auxtype=auxtype(at)entry=StartupProcess) at /mnt/resource/bf/build/mylodon/HEAD/pgsql.build/../pgsql/src/backend/postmaster/auxprocess.c:141
#12 0x00000000007a5891 in StartChildProcess (type=type(at)entry=StartupProcess) at /mnt/resource/bf/build/mylodon/HEAD/pgsql.build/../pgsql/src/backend/postmaster/postmaster.c:5417
#13 0x00000000007a3ea0 in PostmasterMain (argc=argc(at)entry=4, argv=<optimized out>, argv(at)entry=0x1d1cc90) at /mnt/resource/bf/build/mylodon/HEAD/pgsql.build/../pgsql/src/backend/postmaster/postmaster.c:1457
#14 0x00000000006f1b91 in main (argc=4, argv=0x1d1cc90) at /mnt/resource/bf/build/mylodon/HEAD/pgsql.build/../pgsql/src/backend/main/main.c:202
$1 = {si_signo = 6, si_errno = 0, si_code = -6, _sifields = {_pad = {675836, 1001, 0 <repeats 26 times>}, _kill = {si_pid = 675836, si_uid = 1001}, _timer = {si_tid = 675836, si_overrun = 1001, si_sigval = {sival_int = 0, sival_ptr = 0x0}}, _rt = {si_pid = 675836, si_uid = 1001, si_sigval = {sival_int = 0, sival_ptr = 0x0}}, _sigchld = {si_pid = 675836, si_uid = 1001, si_status = 0, si_utime = 0, si_stime = 0}, _sigfault = {si_addr = 0x3e9000a4ffc, _addr_lsb = 0, _addr_bnd = {_lower = 0x0, _upper = 0x0}}, _sigpoll = {si_band = 4299262939132, si_fd = 0}}}

Probably deserves investigation.

regards, tom lane

[1] https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=mylodon&dt=2022-04-15%2011%3A51%3A35