| CC: | imesmits [...] xs4all.nl |
| Subject: | DBD::Pg segfault near dbdimp.c:312 under mod_perl w/stacktrace |
In a mod_perl under some conditions an apache2 process crashes with
signal 11 (SEGV). This happens when postgres notifies the webserver of
underlying schema changes triggered by executing a prepare_cached
statement; the app tries to resolve the error by issueing an automated
disconnect/connect. Although the connect runs fine, the first execution
after the reconnect dumps core in XS function pg_warn. Development box
runs FC13, DBD::Pg 1.17.1 on perl 5.10.0
FATAL ERROR
Program received signal SIGSEGV, Segmentation fault.
0xb6213bd2 in pg_warn (arg=0x2dcb890, message=0x2ebc492 "column number
23 is out of range 0..-1\n") at dbdimp.c:312
PROBABLE SUSPECT
SvROK(SvMAGIC(SvRV(tmp))->mg_obj)
CONTEXT FROM dbdimmp.c line 312
static void pg_warn (void * arg, const char * message)
{
dTHX;
SV *tmp;
tmp = sv_2mortal(newRV_inc((SV *)arg));
/* This fun little bit is to prevent a core dump when the
following occurs:
client_min_messages is set to DEBUG3 or greater, and we exit
without a disconnect.
DBI issues a 'rollback' in this case, which causes some
debugging messages
to be emitted from the server (such as
"StartTransactionCommand"). However, we can't do
the D_imp_dbh call anymore, because the underlying dbh has
lost some of its magic.
Unfortunately, DBI then coredumps in dbh_getcom2. Hence, we
make sure that the
object passed in is still 'valid', in that a certain level
has a ROK flag.
If it's not, we just return without issuing any warning, as
we can't check things
like DBIc_WARN. There may be a better way of handling all
this, and we may want to
default to always warn() - input welcome.
*/
if (!SvROK(SvMAGIC(SvRV(tmp))->mg_obj)) {
return;
}
GDB STACKTRACE
#0 0xb6213bd2 in pg_warn (arg=0x2dcb890, message=0x2ebc492 "column
number 23 is out of range 0..-1\n") at dbdimp.c:312
#1 0xb5f9de09 in defaultNoticeReceiver (arg=0x0, res=0x2f07360) at
fe-connect.c:3758
#2 0xb5fa150c in pqInternalNotice (hooks=0x2f679ac, fmt=0xb5fb1dc8
"column number %d is out of range 0..%d") at fe-exec.c:842
#3 0xb5fa18de in check_field_number (res=<value optimized out>,
field_num=<value optimized out>) at fe-exec.c:2453
#4 0xb5fa1afd in PQfname (res=0x2f67948, field_num=23) at fe-exec.c:2506
#5 0xb6216008 in pg_st_FETCH_attrib (sth=0x2eafcc0, imp_sth=0x2e94868,
keysv=0x2ec5088) at dbdimp.c:1059
#6 0xb61f986b in XS_DBD__Pg__st_FETCH_attrib (my_perl=0x1791d30,
cv=0x1809cc0) at Pg.xsi:732
#7 0xb6d499ca in XS_DBI_dispatch (my_perl=<value optimized out>,
cv=<value optimized out>) at DBI.xs:3292
#8 0xb7a1f6ab in Perl_pp_entersub (my_perl=0x1791d30) at pp_hot.c:2888
#9 0xb6241347 in pp_subcall_profiler (my_perl=0x1791d30, is_slowop=0)
at NYTProf.xs:2457
#10 0xb7a1d818 in Perl_runops_standard (my_perl=0x1791d30) at run.c:40
#11 0xb79be6d1 in Perl_call_sv (my_perl=0x1791d30, sv=0x2e98f80,
flags=64) at perl.c:2702
#12 0xb79c0ce4 in Perl_call_method (my_perl=0x1791d30,
methname=0xb7abd2e8 "FETCH", flags=0) at perl.c:2633
#13 0xb7a0f577 in S_magic_methcall (my_perl=0x1791d30, sv=0x2ea8ca8,
mg=0x2ec44b0, meth=0xb7abd2e8 "FETCH", flags=0, n=2, val=0x0) at mg.c:1698
#14 0xb7a0faf6 in S_magic_methpack (my_perl=0x1791d30, sv=0x2ea8ca8,
mg=0x2ec44b0, meth=0xb7abd2e8 "FETCH") at mg.c:1712
#15 0xb7a0fcd9 in Perl_magic_getpack (my_perl=0x1791d30, sv=0x2ea8ca8,
mg=0x2ec44b0) at mg.c:1729
#16 0xb7a13588 in Perl_mg_get (my_perl=0x1791d30, sv=0x2ea8ca8) at mg.c:221
#17 0xb7a315d7 in Perl_sv_setsv_flags (my_perl=0x1791d30,
dstr=0x2f63fc0, sstr=<value optimized out>, flags=18) at sv.c:3714
#18 0xb7a31e83 in Perl_newSVsv (my_perl=0x1791d30, old=0x2ea8ca8) at
sv.c:7723
#19 0xb6d424b0 in XS_DBD_____st_fetchrow_hashref (my_perl=<value
optimized out>, cv=<value optimized out>) at DBI.xs:4777
#20 0xb6d499ca in XS_DBI_dispatch (my_perl=<value optimized out>,
cv=<value optimized out>) at DBI.xs:3292
#21 0xb7a1f6ab in Perl_pp_entersub (my_perl=0x1791d30) at pp_hot.c:2888
#22 0xb7a1d818 in Perl_runops_standard (my_perl=0x1791d30) at run.c:40
...
#34 0x0014c2ca in child_main (child_num_arg=<value optimized out>) at
/usr/src/debug/httpd-2.2.15/server/mpm/prefork/prefork.c:662