Mailing List Archive: Segfaults with XML parser: how can I debug this?

Segfaults with XML parser: how can I debug this?

Feb 17, 2000, 7:46 AM

Post #1 of 7 (1925 views)

Hi,
I've got a script useing the XML::Grove modules which is
intermittently crashing with segmentation faults and I'm having trouble
tracking down the problem. I've built everything with debug, setup a
test environment where I can replicate the problem, and I'm running
Apache in -X mode under gdb. After handling around 70 requests OK it
crashes. How can I figure out what's going on here? I suspect it may be
a memory leak somewhere in the XML modules...

Cheers,
John

Program received signal SIGSEGV, Segmentation fault.
0x4011255c in chunk_free (ar_ptr=0x676b50, p=0x85eaaf8) at malloc.c:2960
malloc.c:2960: No such file or directory.
(gdb) bt
#0 0x4011255c in chunk_free (ar_ptr=0x676b50, p=0x85eaaf8) at
malloc.c:2960
#1 0x40112505 in __libc_free (mem=0x85eab00) at malloc.c:2932
#2 0x81075f3 in Perl_safefree (where=0x85eab00) at util.c:173
#3 0x8122f7d in Perl_sv_setsv (dstr=0x83fac44, sstr=0x85db150) at
sv.c:2261
#4 0x811638c in Perl_pp_sassign () at pp_hot.c:133
#5 0x8115bf4 in Perl_runops_debug () at run.c:66
#6 0x80d5782 in perl_call_sv (sv=0x81f939c, flags=4) at perl.c:1317
#7 0x807b51b in perl_call_handler (sv=0x81f939c, r=0x85735fc, args=0x0)
at mod_perl.c:1510
#8 0x807ad4b in perl_run_stacked_handlers (hook=0x8170c79
"PerlHandler",
r=0x85735fc, handlers=0x82314a8) at mod_perl.c:1239
#9 0x807951d in perl_handler (r=0x85735fc) at mod_perl.c:802
#10 0x80934d3 in ap_invoke_handler (r=0x85735fc) at http_config.c:508
#11 0x80a6779 in process_request_internal (r=0x85735fc) at
http_request.c:1214
#12 0x80a67dc in ap_process_request (r=0x85735fc) at http_request.c:1230
#13 0x809e1de in child_main (child_num_arg=0) at http_main.c:4035
#14 0x809e36c in make_child (s=0x81aa49c, slot=0, now=950797951)
at http_main.c:4139
#15 0x809e4c9 in startup_children (number_to_start=4) at
http_main.c:4221
#16 0x809eaf6 in standalone_main (argc=2, argv=0xbffffd14) at
http_main.c:4509
#17 0x809f273 in main (argc=2, argv=0xbffffd14) at http_main.c:4830

--
=== John Banks john@slink.net ===
=== Sitelink Technology http://www.slink.net ===

Re: Segfaults with XML parser: how can I debug this? [ In reply to ]

matt at sergeant

Feb 17, 2000, 8:24 AM

Post #2 of 7 (1866 views)

Permalink

On Thu, 17 Feb 2000, you wrote:
> Hi,
> I've got a script useing the XML::Grove modules which is
> intermittently crashing with segmentation faults and I'm having trouble
> tracking down the problem. I've built everything with debug, setup a
> test environment where I can replicate the problem, and I'm running
> Apache in -X mode under gdb. After handling around 70 requests OK it
> crashes. How can I figure out what's going on here? I suspect it may be
> a memory leak somewhere in the XML modules...

Does XML::Grove create circular references like XML::DOM? If so you have to
explicitly dispose of the references using the API (I think it's
$doc->dispose with XML::DOM).

Also make sure you're on the latest version of XML::Parser - it's proved
quite stable.

--
<Matt/>

Details: FastNet Software Ltd - XML, Perl, Databases.
Tagline: High Performance Web Solutions
Web Sites: http://come.to/fastnet http://sergeant.org
Available for Consultancy, Contracts and Training.

Re: Segfaults with XML parser: how can I debug this? [ In reply to ]

john at slink

Feb 18, 2000, 8:11 AM

Post #3 of 7 (1860 views)

Permalink

Matt Sergeant wrote:
>
> On Thu, 17 Feb 2000, you wrote:
> > Hi,
> > I've got a script useing the XML::Grove modules which is
> > intermittently crashing with segmentation faults and I'm having trouble
> > tracking down the problem. I've built everything with debug, setup a
> > test environment where I can replicate the problem, and I'm running
> > Apache in -X mode under gdb. After handling around 70 requests OK it
> > crashes. How can I figure out what's going on here? I suspect it may be
> > a memory leak somewhere in the XML modules...
>
> Does XML::Grove create circular references like XML::DOM? If so you have to
> explicitly dispose of the references using the API (I think it's
> $doc->dispose with XML::DOM).
>
> Also make sure you're on the latest version of XML::Parser - it's proved
> quite stable.
>

Thanks for the comments. There doesn't appear to be an equivalent to the
dispose method for XML::Grove - if circular refences don't get cleaned
up I can see how the process size would grow, but it shouldn't make it
segfault(?) I've got XML::Parser 2.27 so I don't think that's the
problem.

John

--
=== John Banks john@slink.net ===
=== Sitelink Technology http://www.slink.net ===

Re: Segfaults with XML parser: how can I debug this? [ In reply to ]

matt at sergeant

Feb 18, 2000, 9:34 AM

Post #4 of 7 (1861 views)

Permalink

On Fri, 18 Feb 2000, John Banks wrote:
> Matt Sergeant wrote:
> >
> > On Thu, 17 Feb 2000, you wrote:
> > > Hi,
> > > I've got a script useing the XML::Grove modules which is
> > > intermittently crashing with segmentation faults and I'm having trouble
> > > tracking down the problem. I've built everything with debug, setup a
> > > test environment where I can replicate the problem, and I'm running
> > > Apache in -X mode under gdb. After handling around 70 requests OK it
> > > crashes. How can I figure out what's going on here? I suspect it may be
> > > a memory leak somewhere in the XML modules...
> >
> > Does XML::Grove create circular references like XML::DOM? If so you have to
> > explicitly dispose of the references using the API (I think it's
> > $doc->dispose with XML::DOM).
> >
> > Also make sure you're on the latest version of XML::Parser - it's proved
> > quite stable.
> >
>
> Thanks for the comments. There doesn't appear to be an equivalent to the
> dispose method for XML::Grove - if circular refences don't get cleaned
> up I can see how the process size would grow, but it shouldn't make it
> segfault(?) I've got XML::Parser 2.27 so I don't think that's the
> problem.

I'd suggest dropping a line to Clark Cooper then with a core dump or
something he can go on to debug the problem. Are you certain it's an
XML::Parser problem?

--
<Matt/>

Details: FastNet Software Ltd - XML, Perl, Databases.
Tagline: High Performance Web Solutions
Web Sites: http://come.to/fastnet http://sergeant.org
Available for Consultancy, Contracts and Training.

Re: Segfaults with XML parser: how can I debug this? [ In reply to ]

matt at sergeant

Feb 18, 2000, 9:34 AM

Post #5 of 7 (1869 views)

Permalink

Re: Segfaults with XML parser: how can I debug this? [ In reply to ]

john at slink

Feb 18, 2000, 2:03 PM

Post #6 of 7 (1883 views)

Permalink

Matt Sergeant wrote:
>
> On Fri, 18 Feb 2000, John Banks wrote:
> > Matt Sergeant wrote:
> > >
> > > On Thu, 17 Feb 2000, you wrote:
> > > > Hi,
> > > > I've got a script useing the XML::Grove modules which is
> > > > intermittently crashing with segmentation faults and I'm having trouble
> > > > tracking down the problem. I've built everything with debug, setup a
> > > > test environment where I can replicate the problem, and I'm running
> > > > Apache in -X mode under gdb. After handling around 70 requests OK it
> > > > crashes. How can I figure out what's going on here? I suspect it may be
> > > > a memory leak somewhere in the XML modules...
> > >
> > > Does XML::Grove create circular references like XML::DOM? If so you have to
> > > explicitly dispose of the references using the API (I think it's
> > > $doc->dispose with XML::DOM).
> > >
> > > Also make sure you're on the latest version of XML::Parser - it's proved
> > > quite stable.
> > >
> >
> > Thanks for the comments. There doesn't appear to be an equivalent to the
> > dispose method for XML::Grove - if circular refences don't get cleaned
> > up I can see how the process size would grow, but it shouldn't make it
> > segfault(?) I've got XML::Parser 2.27 so I don't think that's the
> > problem.
>
> I'd suggest dropping a line to Clark Cooper then with a core dump or
> something he can go on to debug the problem. Are you certain it's an
> XML::Parser problem?
>

No, I'm not sure it's the XML modules which are the culprit, that's what
I'm trying to figure out - the traceback from the coredump is not very
helpful :-( I'll see if I can put together a small self contained
script which replicates the problem...

John

--
=== John Banks john@slink.net ===
=== Sitelink Technology http://www.slink.net ===

Re: Segfaults with XML parser: how can I debug this? [ In reply to ]

doyle at aps

Feb 18, 2000, 3:14 PM

Post #7 of 7 (1879 views)

Permalink

Greetings,

> From: John Banks <john@slink.net>
> Date: 2000-02-18 21:03:53 -0500

> Matt Sergeant wrote:

> > I'd suggest dropping a line to Clark Cooper then with a core dump or
> > something he can go on to debug the problem. Are you certain it's an
> > XML::Parser problem?
> >
>
> No, I'm not sure it's the XML modules which are the culprit, that's what
> I'm trying to figure out - the traceback from the coredump is not very
> helpful :-( I'll see if I can put together a small self contained
> script which replicates the problem...

I think it may be a problem with XML::Parser - I have a fairly
straightforwad mod_perl script that uses (a subclass of) XML::Parser. Today
(based on the messages here), I decided it probably would be best to upgrade
to 2.27 - when I did that I consistently got segfaults/core dumps. Rolling
back to 2.19 made the problem go away. I don't have a debug build, so I can't
provide more info at this point. But something funny is going on (this is
with apache 1.3.9, mod_perl 1.21 on Solaris 7).

Cheers,
Mark