BUG #19482: Recursive QueueFKConstraintValidation() lacks stack depth check

The following bug has been logged on the website:

Bug reference: 19482
Logged by: Alexander Lakhin
Email address: exclusion(at)gmail(dot)com
PostgreSQL version: 18.4
Operating system: Ubuntu 24.04
Description:

The following script:
echo "
CREATE TABLE tp0 (a int, PRIMARY KEY (a)) PARTITION BY RANGE(a);
ALTER TABLE tp0 ADD CONSTRAINT fk FOREIGN KEY (a) REFERENCES tp0 NOT VALID;
" | psql

for ((i=1;i<=48000;i++)); do # may take 2-3 hours
echo "CREATE TABLE tp$i PARTITION OF tp$(( $i - 1 ))
FOR VALUES FROM ($i) TO (1000000) PARTITION BY RANGE (a);";
done | psql > psql.log

echo "
ALTER TABLE tp0 VALIDATE CONSTRAINT fk;
" | psql

leads to:
2026-05-16 12:35:43.258 EEST|law|regression|6a083a6f.34aa38|LOG: statement:
ALTER TABLE tp0 VALIDATE CONSTRAINT fk;
2026-05-16 12:35:56.104 EEST|||6a07f1d1.32a4c7|LOG: client backend (PID
3451448) was terminated by signal 11: Segmentation fault
2026-05-16 12:35:56.104 EEST|||6a07f1d1.32a4c7|DETAIL: Failed process was
running: ALTER TABLE tp0 VALIDATE CONSTRAINT fk;

Core was generated by `postgres: law regression 127.0.0.1(48420) ALTER TABLE
'.
Program terminated with signal SIGSEGV, Segmentation fault.
#0 0x00005e57e8d06ae9 in hash_initial_lookup (hashp=0x5e580f378e10,
hashvalue=795799848, bucketptr=0x7ffe0c940090) at dynahash.c:1767
1767 bucket = calc_bucket(hctl, hashvalue);
(gdb) (gdb) (gdb) (gdb) #0 0x00005e57e8d06ae9 in hash_initial_lookup
(hashp=0x5e580f378e10, hashvalue=795799848, bucketptr=0x7ffe0c940090) at
dynahash.c:1767
#1 0x00005e57e8d0545c in hash_search_with_hash_value (hashp=0x5e580f378e10,
keyPtr=0x7ffe0c94010c, hashvalue=795799848, action=HASH_FIND, foundPtr=0x0)
at dynahash.c:1010
#2 0x00005e57e8d0538a in hash_search (hashp=0x5e580f378e10,
keyPtr=0x7ffe0c94010c, action=HASH_FIND, foundPtr=0x0) at dynahash.c:961
#3 0x00005e57e8a7c224 in GetPrivateRefCountEntry (buffer=125, do_move=true)
at bufmgr.c:381
#4 0x00005e57e8a8051a in PinBuffer (buf=0x762990250980, strategy=0x0) at
bufmgr.c:3085
...
#20 0x00005e57e8ce0a15 in CheckNNConstraintFetch (relation=0x762989504168)
at relcache.c:4619
#21 0x00005e57e8cd9b66 in RelationBuildTupleDesc (relation=0x762989504168)
at relcache.c:701
#22 0x00005e57e8cdaa23 in RelationBuildDesc (targetRelId=464701,
insertIt=true) at relcache.c:1204
#23 0x00005e57e8cdc5cb in RelationIdGetRelation (relationId=464701) at
relcache.c:2142
#24 0x00005e57e84d14d2 in relation_open (relationId=464701, lockmode=4) at
relation.c:58
#25 0x00005e57e85a16c8 in table_open (relationId=464701, lockmode=4) at
table.c:44
#26 0x00005e57e877c41b in QueueFKConstraintValidation
(wqueue=0x7ffe0d13d128, conrel=0x76299e17b6d0, fkrel=0x7629895039e8,
pkrelid=16385,
contuple=0x5e5850492148, lockmode=4) at tablecmds.c:13080
#27 0x00005e57e877c450 in QueueFKConstraintValidation
(wqueue=0x7ffe0d13d128, conrel=0x76299e17b6d0, fkrel=0x762989503268,
pkrelid=16385,
contuple=0x5e5850491c98, lockmode=4) at tablecmds.c:13086
#28 0x00005e57e877c450 in QueueFKConstraintValidation
(wqueue=0x7ffe0d13d128, conrel=0x76299e17b6d0, fkrel=0x762989502ae8,
pkrelid=16385,
contuple=0x5e58504917e8, lockmode=4) at tablecmds.c:13086
...
#37383 0x00005e57e877c450 in QueueFKConstraintValidation
(wqueue=0x7ffe0d13d128, conrel=0x76299e17b6d0, fkrel=0x76299dd9b218,
pkrelid=16385,
contuple=0x5e580f357b98, lockmode=4) at tablecmds.c:13086
#37384 0x00005e57e877c450 in QueueFKConstraintValidation
(wqueue=0x7ffe0d13d128, conrel=0x76299e17b6d0, fkrel=0x76299dd98358,
pkrelid=16385,
contuple=0x5e580f35d628, lockmode=4) at tablecmds.c:13086
#37385 0x00005e57e877c025 in ATExecValidateConstraint
(wqueue=0x7ffe0d13d128, rel=0x76299dd98358, constrName=0x5e580f3554d8 "fk",
recurse=true,
recursing=false, lockmode=4) at tablecmds.c:12966
#37386 0x00005e57e876acde in ATExecCmd (wqueue=0x7ffe0d13d128,
tab=0x5e580f354fc8, cmd=0x5e580f355488, lockmode=4, cur_pass=AT_PASS_MISC,
context=0x7ffe0d13d320) at tablecmds.c:5497
#37387 0x00005e57e876a347 in ATRewriteCatalogs (wqueue=0x7ffe0d13d128,
lockmode=4, context=0x7ffe0d13d320) at tablecmds.c:5334
#37388 0x00005e57e876968c in ATController (parsetree=0x5e580f32aa88,
rel=0x76299dd98358, cmds=0x5e580f32aa38, recurse=true, lockmode=4,
context=0x7ffe0d13d320)
at tablecmds.c:4889
#37389 0x00005e57e876929d in AlterTable (stmt=0x5e580f32aa88, lockmode=4,
context=0x7ffe0d13d320) at tablecmds.c:4544
#37390 0x00005e57e8ae8380 in ProcessUtilitySlow (pstate=0x5e580f354470,
pstmt=0x5e580f32ab38,
queryString=0x5e580f329f60 "ALTER TABLE tp0 VALIDATE CONSTRAINT fk;",
context=PROCESS_UTILITY_TOPLEVEL, params=0x0, queryEnv=0x0,
dest=0x5e580f32aef8,
qc=0x7ffe0d13d980) at utility.c:1321

Reproduced on REL_18_STABLE, starting from b663b9436, and on master.