Обсуждение: Fwd: Segmentation fault on RelationGetDescr in my first extension

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Fwd: Segmentation fault on RelationGetDescr in my first extension

От
Дмитрий Цветков
Дата:
Hi!

I'm trying to write my first extension and open a table in it.
I use check_password_hook and my function executes at the moment of changing user password.

But if I try to open a table inside this function, I get Segmentation fault on the line with   "RelationGetDescr".
What am I doing wrong?

void
_PG_init(void)
{
prev_check_password_hook = check_password_hook;
check_password_hook = check_password;
}

...

void check_password(const char *username, const char *shadow_pass, PasswordType password_type, Datum validuntil_time, bool validuntil_null)
{
Relation rel;
TupleDesc tupdesc;
int Natts;

Oid tbl_oid = DatumGetObjectId(DirectFunctionCall1(to_regclass, CStringGetTextDatum("my_test_table")));
if (OidIsValid(tbl_oid)) {
rel = table_open(tbl_oid, RowExclusiveLock);
tupdesc = RelationGetDescr(rel); // !!! server process (PID 70525) was terminated by signal 11: Segmentation fault
Natts = tupdesc->natts;
table_close(rel, RowExclusiveLock);
} else {
ereport(NOTICE, (errmsg("IndexRelationId (%d) is NOT valid !", tbl_oid)));
}
}

Table is fine:

postgres=# \d my_test_table
          Table "public.my_test_table"
 Column | Type | Collation | Nullable | Default
--------+------+-----------+----------+---------
 name   | text |           |          |

Re: Segmentation fault on RelationGetDescr in my first extension

От
Kyotaro Horiguchi
Дата:
At Thu, 29 Dec 2022 13:52:18 +0300, Дмитрий Цветков <dmitry.cvetkov@gmail.com> wrote in
> I'm trying to write my first extension and open a table in it.
> I use check_password_hook and my function executes at the moment of
> changing user password.
>
> But if I try to open a table inside this function, I get Segmentation fault
> on the line with   "RelationGetDescr".
> What am I doing wrong?

table_open() should error out when it is going to return an invalid
Relation*, and RelationGetDescr(rel) is "rel->rd_att". So the
RelationGetDescr() cannot get a segv even if the table does not exist.

# I modified contrib/passwordcheck that way and saw RelationGetDescr()
# doesn't get segv in the shown context.

I guess the segv comes from another place, or something else has
broken memory until there. but anyway more information is needed for
people to diagnose your situation more closely.

regards.

--
Kyotaro Horiguchi
NTT Open Source Software Center