[pypy-dev] Debugging "cannot find gc roots!"

[Alex Gaynor]

On Sat, Jun 25, 2011 at 1:11 AM, Armin Rigo <arigo at tunes.org> wrote:

> Hi Alex,
>
> On Sat, Jun 25, 2011 at 3:11 AM, Alex Gaynor <alex.gaynor at gmail.com>
> wrote:
> > In running my application I hit a "cannot find gc roots!", it reproduces
> > reliably, but it's a pain to isolate because it occurs in a very large
> > application, running under paste, with threads :(
>
> You should rebuild pypy with "make lldebug".  Then gdb should stop as
> soon as the crash is found.
>
>
> Armin
>

Hrm, this is pretty strange, running an lldebug build, not under gdb
reliably produces a crash:

alex at devalex:~/ans/venv/answeb$ ANS_INSTANCE=dwc pypy ../lib/pypy/bin/paster
serve --reload alex-dev.ini
Starting subprocess with file monitor
overriding ans instance based on environment: dwc
Starting server in PID 6809.
serving on 0.0.0.0:5050 view at http://127.0.0.1:5050
cannot find gc roots!
debug_alloc.h: 9 mallocs left (use PYPY_ALLOC=1 to see the list)

However, running under gdb results in broken pip errors from a socket (this
is a web app in case that wasn't clear):

alex at devalex:~/ans/venv/answeb$ ANS_INSTANCE=dwc gdb --args pypy
../lib/pypy/bin/paster serve --reload alex-dev.ini
GNU gdb (GDB) 7.1-ubuntu
Copyright (C) 2010 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html
>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "x86_64-linux-gnu".
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>...
Reading symbols from /home/alex/ans/venv/bin/pypy...(no debugging symbols
found)...done.
(gdb) run
Starting program: /home/alex/ans/venv/bin/pypy ../lib/pypy/bin/paster serve
--reload alex-dev.ini
warning: the debug information found in "/lib/ld-2.11.1.so" does not match
"/lib/ld-linux.so.2" (CRC mismatch).

warning: the debug information found in "/usr/lib/debug//lib/ld-2.11.1.so"
does not match "/lib/ld-linux.so.2" (CRC mismatch).

warning: the debug information found in "/usr/lib/debug/lib/ld-2.11.1.so"
does not match "/lib/ld-linux.so.2" (CRC mismatch).

[Thread debugging using libthread_db enabled]
Starting subprocess with file monitor
overriding ans instance based on environment: dwc
Starting server in PID 6743.
serving on 0.0.0.0:5050 view at http://127.0.0.1:5050
----------------------------------------
Exception happened during processing of request from ('10.160.27.96', 44587)
Traceback (most recent call last):
  File "/home/alex/ans/venv/lib/pypy/site-packages/paste/httpserver.py",
line 1068, in process_request_in_thread
    self.finish_request(request, client_address)
  File "/home/alex/ans/venv/lib/pypy/lib-python/2.7/SocketServer.py", line
323, in finish_request
    self.RequestHandlerClass(request, client_address, self)
  File "/home/alex/ans/venv/lib/pypy/lib-python/2.7/SocketServer.py", line
641, in __init__
    self.finish()
  File "/home/alex/ans/venv/lib/pypy/lib-python/2.7/SocketServer.py", line
694, in finish
    self.wfile.flush()
  File "/home/alex/ans/venv/lib/pypy/lib-python/modified-2.7/socket.py",
line 348, in flush
    self._sock.sendall(view[write_offset:write_offset+buffer_size])
  File "/home/alex/ans/venv/lib/pypy/lib-python/modified-2.7/socket.py",
line 266, in sendall
    self._sock.sendall(data, flags)
error: [Errno 32] Broken pipe
----------------------------------------
----------------------------------------
Exception happened during processing of request from ('10.160.27.96', 44608)
Traceback (most recent call last):
  File "/home/alex/ans/venv/lib/pypy/site-packages/paste/httpserver.py",
line 1068, in process_request_in_thread
    self.finish_request(request, client_address)
  File "/home/alex/ans/venv/lib/pypy/lib-python/2.7/SocketServer.py", line
323, in finish_request
    self.RequestHandlerClass(request, client_address, self)
  File "/home/alex/ans/venv/lib/pypy/lib-python/2.7/SocketServer.py", line
641, in __init__
    self.finish()
  File "/home/alex/ans/venv/lib/pypy/lib-python/2.7/SocketServer.py", line
694, in finish
    self.wfile.flush()
  File "/home/alex/ans/venv/lib/pypy/lib-python/modified-2.7/socket.py",
line 348, in flush
    self._sock.sendall(view[write_offset:write_offset+buffer_size])
  File "/home/alex/ans/venv/lib/pypy/lib-python/modified-2.7/socket.py",
line 266, in sendall
    self._sock.sendall(data, flags)
error: [Errno 32] Broken pipe
----------------------------------------
----------------------------------------


The only thing worth noting is that this a 32-bit PyPy on a 64-bit OS (the
gdb is also 64-bits, so if that matters the gdb runs may not be valid).  I'm
not sure whether I see the socket issue with gdb because its dieing earlier
than the gc roots issue, or if it's because the error doesn't appear for
some reason, and therefore it gets farther and hits a second issue.

Alex


-- 
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