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https://issues.apache.org/jira/browse/DISPATCH-1962?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Jiri Daněk reassigned DISPATCH-1962:
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Assignee: Jiri Daněk
> Make LSan suppressions more targeted and specific (within reason)
> -----------------------------------------------------------------
>
> Key: DISPATCH-1962
> URL: https://issues.apache.org/jira/browse/DISPATCH-1962
> Project: Qpid Dispatch
> Issue Type: Test
> Affects Versions: 1.15.0
> Reporter: Jiri Daněk
> Assignee: Jiri Daněk
> Priority: Major
> Fix For: 1.16.0
>
> Attachments: dispatch_leaking_agent.png
>
>
> There are some unfortunate suppressions in {{tests/lsan.supp}} at this moment:
> {code}
> leak:*libwebsockets*
> {code}
> This is way too broad. It suppresses leaks in Dispatch files, since it
> matches e.g. {{src/http-libwebsockets.c}}.
> The stars at the beginning and end are actually assumed implicitly. If you do
> not want substring match, you have to do ^foo$. LSan suppression format is
> simplistic, very unlike Valgrind's.
> {code}
> leak:run_unit_tests.c
> {code}
> Same thing, any leaks revealed by running unit_tests get suppressed. This
> suppression suppresses all leak traces that include run_unit_tests.c anywhere
> in the stack. What't the point of running such tests under leak detector,
> then?
> {code}
> leak:run_unit_tests.c
> leak:^libqpid-proton.so$
> {code}
> Same thing. The patterns suppress all leaks that include Python (or Proton)
> anywhere in the stacktrace. That means there are huge blind spots where
> dispatch leaks can hide. This is a weakness of the lsan.supp syntax (Valgrind
> suppressions can be much more targeted and discerning).
> h3. Python leaks
> Leaks are known and there is ongoing effort to fight them:
> https://bugs.python.org/issue1635741 (https://bugs.python.org/issue25302) and
> https://www.python.org/dev/peps/pep-3121
> Here's valgrind suppression file from somebody who actually investigated the
> Python leaks and identified the harmless ones:
> https://github.com/libgit2/pygit2/blob/master/misc/valgrind-python.supp
> One example of a hidden leak in dispatch, which is revealed by making Python
> suppressions more targetted:
> {code}
> 9: Direct leak of 56 byte(s) in 1 object(s) allocated from:
> 9: #0 0x7f78a3606e8f in __interceptor_malloc
> (/nix/store/g40sl3zh3nv52vj0mrl4iki5iphh5ika-gcc-10.2.0-lib/lib/libasan.so.6+0xace8f)
> 9: #1 0x7f78a2d64afb in qd_malloc ../include/qpid/dispatch/ctools.h:229
> 9: #2 0x7f78a2d657da in qdr_core_subscribe
> ../src/router_core/route_tables.c:149
> 9: #3 0x7f78a2c83072 in IoAdapter_init ../src/python_embedded.c:711
> 9: #4 0x7f78a2353a6c in type_call
> (/nix/store/r85nxfnwiv45nbmf5yb60jj8ajim4m7w-python3-3.8.5/lib/libpython3.8.so.1.0+0x165a6c)
> {code}
> The problem is in
> {code}
> class Agent:
> ...
> def activate(self, address):
> ...
> self.io = IoAdapter(self.receive, address, 'L', '0',
> TREATMENT_ANYCAST_CLOSEST)
> {code}
> IoAdapter refers to Agent (through the bound method reference self.receive)
> and Agent refers to IoAdapter (through property self.io). Since IoAdapter is
> implemented in C and does not implement support for Python's cyclic GC, there
> is no way to break the cycle.
> Heap dump in attachment. The bound method is at the top of the picture.
> (Ignore the Mock objects, I was trying to simplify the picture while not
> getting crashes due to too much meddling).
> h3. Random observations
> It is possible to build special Debug build of Python, which has tools to
> detect leaks, asserts to prevent negative refcounts, etc.
> https://pythonextensionpatterns.readthedocs.io/en/latest/debugging/debug_python.html#debug-version-of-python-memory-alloc-label
> Use the following to detect python leaks (instead of valgrind)
> https://docs.python.org/3/library/tracemalloc.html
> Use https://pypi.org/project/objgraph (with graphviz) to view heap object
> trees. The following renders the picture as a png under /tmp and prints the
> path to stdout.
> {code}
> int ret = PyRun_SimpleString("import objgraph;
> objgraph.show_backrefs(config.global_agent, max_depth=10)\n\n");
> PyErr_PrintEx(0);
> assert(ret == 0);
> {code}
> h2. Tools
> h3. CPyChecker
> https://dmalcolm.fedorapeople.org/presentations/PyCon-US-2013/PyCon-US-2013-dmalcolm-StaticAnalysis.html#(38)
> https://emptysqua.re/blog/analyzing-python-c-extensions-with-cpychecker/
> https://nedbatchelder.com/blog/201502/cpychecker.html
> h3. Pungi
> http://www.cse.psu.edu/~gxt29/papers/refcount.pdf
> h3. Use CFFI or similar, instead of writing a C module.
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