[pgpool-hackers: 4229] segmentation fault error

[稲垣毅 / INAGAKI，TSUYOSHI]

Hi, Pgpool hackers,

In Pgpool-II4.2.7, process down due to segmentation fault occurs.
The OS is RHEL8 and PostgreSQL 13.2.

When I got the backtrace from core, it was as follows.

(gdb) bt
#0 0x0000559ff3b977f4 in function_call_walker (node=0x1000100000000, context=0x7ffcefcf1390) at utils/pool_select_walker.c:341
#1 0x0000559ff3b9458d in raw_expression_tree_walker (node=0x559ff531aa10, walker=0x559ff3b977e0 <function_call_walker>, context=0x7ffcefcf1390) at rewrite/pool_timestamp.c:1454
#2 0x0000559ff3b9446d in raw_expression_tree_walker (node=0x559ff53147c8, walker=0x559ff3b977e0 <function_call_walker>, context=0x7ffcefcf1390) at rewrite/pool_timestamp.c:1518
#3 0x0000559ff3b9646c in pool_has_function_call (node=node �� entry=0x559ff53147c8) at utils/pool_select_walker.c:73
#4 0x0000559ff3b7bb6c in Execute (frontend=frontend �� entry=0x559ff52dbb78, backend=backend �� entry=0x7f545af010e8, len=9, contents=contents �� entry=0x559ff52e1b98 "C_60") at protocol/pool_proto_modules.c:1077
#5 0x0000559ff3b8205e in ProcessFrontendResponse (frontend=frontend �� entry=0x559ff52dbb78, backend=backend �� entry=0x7f545af010e8) at protocol/pool_proto_modules.c:2708
#6 0x0000559ff3b739e3 in read_packets_and_process (frontend=<optimized out>, backend=<optimized out>, reset_request=<optimized out>, state=<optimized out>, num_fields=<optimized out>, cont=<optimized out>)
    at protocol/pool_process_query.c:4941
#7 0x0000559ff3b742b3 in pool_process_query (frontend=<optimized out>, backend=<optimized out>, reset_request=<optimized out>) at protocol/pool_process_query.c:291
#8 0x0000559ff3b6ce8a in do_child (fds=fds �� entry=0x559ff530de90) at protocol/child.c:449
#9 0x0000559ff3b41527 in fork_a_child (fds=0x559ff530de90, id=731) at main/pgpool_main.c:682
#10 0x0000559ff3b46415 in failover () at main/pgpool_main.c:1996
#11 0x0000559ff3b4579b in sigusr1_interupt_processor () at main/pgpool_main.c:1329
#12 0x0000559ff3b48e4a in PgpoolMain (discard_status=<optimized out>, clear_memcache_oidmaps=<optimized out>) at main/pgpool_main.c:473
#13 0x0000559ff3b3f54c in main (argc=<optimized out>, argv=0x7ffcefd01658) at main/main.c:365
(gdb)

The reason for the abnormal termination is that the value of the argument
node passed to function_call_walker is invalid.
After analyzing the core, the caller is raw_expression_tree_walker,
but the value of nodeTag(node) passed here is 0xE2 and T_List.
Here, the ListCell pointer retrieved by foreach() is invalid.


List structure
(gdb) x/8gx $rbx
0x559ff531aa10: 0x0000000f000000e2 0x000000000000000f
0x559ff531aa20: 0x0000559ff5314000 0x0000559ff531a9c0
0x559ff531aa30: 0x0000000000000008 0x00007f545af1a300
0x559ff531aa40: 0x0000006469727375 0x0000000000000020

(gdb) x/8gx 0x0000559ff5314000
0x559ff5314000: 0x0000000000000000 0x0000000000000000
0x559ff5314010: 0x0000000000000000 0x0001000100000000 <- argument of function_call_walker
0x559ff5314020: 0x0000000000000000 0x0000000000000000
0x559ff5314030: 0x0000000000000000 0x0000000000000000

The previous area is also cleared to 0.
(gdb) x/4gx 0x0000559ff5314000-0x10
0x559ff5313ff0: 0x0000000000000000 0x0000000000000000
0x559ff5314000: 0x0000000000000000 0x0000000000000000

I think that it causes area(memory) destruction, but there is no corresponding bug fix
in the release notes after 4.2.8.
Is it a phenomenon that is recognized as a known defect?

If it is not a known defect, I would like to identify the process causing the area destruction.
What kind of method is there?

Note that this has only occurred once in the production environment,  and at this time we have not been able to reproduce it.

Regards,

--
Tsuyoshi Inagaki
tsuyoshi.inagaki.ej �� hitachi.com<mailto:tsuyoshi.inagaki.ej �� hitachi.com>

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