EN_Destructor bug - Mailing list pgsql-odbc

Hello!

1) We observe crashes in psqlodbc.so library from time to time. Crash dumps
typically look like this one:
#0  0x0057f420 in __kernel_vsyscall ()
#1  0x09ba7df0 in raise () from /lib/libc.so.6
#2  0x09ba9701 in abort () from /lib/libc.so.6
#3  0x09bdebcb in __libc_message () from /lib/libc.so.6
#4  0x09be6fea in _int_free () from /lib/libc.so.6
#5  0x09be7329 in free () from /lib/libc.so.6
#6  0x02c601d0 in EN_Destructor () from /usr/pgsql-9.0/lib/psqlodbc.so
#7  0x02c60224 in PGAPI_FreeEnv () from /usr/pgsql-9.0/lib/psqlodbc.so
#8  0x02c8f3fe in SQLFreeHandle () from /usr/pgsql-9.0/lib/psqlodbc.so
#9  0x00e961e5 in ?? () from /usr/lib/libodbc.so.1
#10 0x00e9666d in ?? () from /usr/lib/libodbc.so.1
#11 0x00e96760 in ?? () from /usr/lib/libodbc.so.1
#12 0x00e9d02e in SQLDisconnect () from /usr/lib/libodbc.so.1
…
Due to nature of our program it makes frequent connect / disconnects in
parallel threads. ODBC threading level is set to 2, e.g.:
[PostgreSQL]
Description     = PostgreSQL driver
Driver          = /usr/pgsql-9.0/lib/psqlodbc.so
Setup           = /usr/pgsql-9.0/lib/psqlodbc.so
FileUsage       = 1
Threading = 2
2) Checking code of driver reveals that it doesn’t protect shared connection
list when making cleanup tasks in EN_Destructor (PGAPI_FreeEnv ->
EN_Destructor). In this function there is no ENTER_CONNS_CS /
LEAVE_CONNS_CS;
3)  In 2005 Tom Hughes
(http://postgresql.1045698.n5.nabble.com/EN-Destructor-bug-td2187457.html)
provided patch that fixed this problem but then his changes were lost
(starting from psqlodbc-08.02.0100 version).
4) The problem was reproduced on latest stock drivers psqlodbc-09.00.0310
and psqlodbc-09.01.0200.
5) When logging to mylog is enrolled then problem is hardly reproduced – it
seems parallels calls are effectively serialized within mylog() function.
6) Problem is somewhat mitigated by the fact that default threading level in
unixODBC is set to 3 which eventually prevents races in psqlodbc driver.
7) Patch:
--- environ.c.van       2010-08-21 10:29:19.000000000 +0400
+++ environ.c   2013-01-17 18:47:12.000000000 +0300
@@ -583,6 +583,7 @@
         */

        /* Free any connections belonging to this environment */
+       ENTER_CONNS_CS;
        for (lf = 0, nullcnt = 0; lf < conns_count; lf++)
        {
                if (NULL == conns[lf])
@@ -603,6 +604,7 @@
                conns = NULL;
                conns_count = 0;
        }
+       LEAVE_CONNS_CS;
        DELETE_ENV_CS(self);
        free(self);

Thanks!

Michael Kocherov
Software Developer
Parallels Automation Maintenance




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