python_bindings: Fix SIGSEGV in HalidePythonCompileTimeErrorReporter

[knzivid]

When I realize g in the snippet below, I get a SIGSEGV in PyErr_Occurred. This example is run with python bindings from release/13.x branch.

Expected: I see the warning

Warning: It is meaningless to bound dimension v0 of function f to be within [0, 127]
because the function is scheduled inline.

Actual: SIGSEGV

I added a py::gil_scoped_acquire before printing similar to halide_python_print() in PyError.cpp and this fixes the output. Should I release the GIL?

buffer = Buffer(np.arange(2048))
i = Var()
f = Func("f")
f[i] = buffer[i]
f.bound(i, 0, 127)

g = Func("g")
g[i] = f[i * i]
g.realize([16])

Thread 1 "python" received signal SIGSEGV, Segmentation fault.
0x00007fa43811932e in PyErr_Occurred () from /usr/lib/libpython3.9.so.1.0
(gdb) bt
#0  0x00007fa43811932e in PyErr_Occurred () from /usr/lib/libpython3.9.so.1.0
#1  0x00007fa43725600b in pybind11::arg_v::arg_v<char const (&) [1]> (this=0x7fa408f31e88, base=..., x={...}, descr=0x0) at Halide/cmake-build-debug/_deps/pybind11-src/include/pybind11/cast.h:1902
#2  0x00007fa437255f4b in pybind11::arg_v::arg_v<char const (&) [1]> (this=0x7fa408f31e88, base=..., x={...}, descr=0x0) at Halide/cmake-build-debug/_deps/pybind11-src/include/pybind11/cast.h:1916
#3  0x00007fa437235a09 in pybind11::arg::operator=<char const (&) [1]> (this=0x7fa408f31e78, value={...}) at Halide/cmake-build-debug/_deps/pybind11-src/include/pybind11/cast.h:1945
#4  0x00007fa4372db272 in Halide::PythonBindings::(anonymous namespace)::HalidePythonCompileTimeErrorReporter::warning (this=0x7fa437847f98 <Halide::PythonBindings::define_error(pybind11::module_&)::reporter>, msg=0x558ddf3937c0 "Warning: It is meaningless to bound dimension v0 of function f to be within [0, 127] because the function is scheduled inline.\n") at Halide/python_bindings/src/PyError.cpp:20
#5  0x00007fa4328d5d4f in Halide::Internal::ErrorReport::~ErrorReport (this=0x7fa408f32578) at Halide/src/Error.cpp:110
#6  0x00007fa432a9e949 in Halide::Internal::validate_schedule_inlined_function (f=...) at Halide/src/Inline.cpp:80
#7  0x00007fa432d03719 in Halide::Internal::(anonymous namespace)::validate_schedule (f=..., s=..., target=..., is_output=false, env=std::map with 2 elements = {...}) at Halide/src/ScheduleFunctions.cpp:2194
#8  0x00007fa432d0101e in Halide::Internal::schedule_functions (outputs=std::vector of length 1, capacity 1 = {...}, fused_groups=std::vector of length 2, capacity 2 = {...}, env=std::map with 2 elements = {...}, target=..., any_memoized=@0x7fa408f3624f: false) at Halide/src/ScheduleFunctions.cpp:2442
#9  0x00007fa432c085f6 in Halide::Internal::(anonymous namespace)::lower_impl (output_funcs=std::vector of length 1, capacity 1 = {...}, pipeline_name="g", t=..., args=std::vector of length 2, capacity 2 = {...}, linkage_type=Halide::LinkageType::ExternalPlusMetadata, requirements=std::vector of length 0, capacity 0, trace_pipeline=false, custom_passes=std::vector of length 0, capacity 0, result_module=...) at Halide/src/Lower.cpp:143
#10 0x00007fa432c081c4 in Halide::Internal::lower(std::vector<Halide::Internal::Function, std::allocator<Halide::Internal::Function> > const&, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, Halide::Target const&, std::vector<Halide::Argument, std::allocator<Halide::Argument> > const&, Halide::LinkageType, std::vector<Halide::Internal::Stmt, std::allocator<Halide::Internal::Stmt> > const&, bool, std::vector<Halide::Internal::IRMutator*, std::allocator<Halide::Internal::IRMutator*> > const&)::$_0::operator()() const (this=0x558ddf5e4eb0) at Halide/src/Lower.cpp:539
#11 0x00007fa432c0814d in std::__invoke_impl<void, Halide::Internal::lower(std::vector<Halide::Internal::Function, std::allocator<Halide::Internal::Function> > const&, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, Halide::Target const&, std::vector<Halide::Argument, std::allocator<Halide::Argument> > const&, Halide::LinkageType, std::vector<Halide::Internal::Stmt, std::allocator<Halide::Internal::Stmt> > const&, bool, std::vector<Halide::Internal::IRMutator*, std::allocator<Halide::Internal::IRMutator*> > const&)::$_0&>(std::__invoke_other, Halide::Internal::lower(std::vector<Halide::Internal::Function, std::allocator<Halide::Internal::Function> > const&, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, Halide::Target const&, std::vector<Halide::Argument, std::allocator<Halide::Argument> > const&, Halide::LinkageType, std::vector<Halide::Internal::Stmt, std::allocator<Halide::Internal::Stmt> > const&, bool, std::vector<Halide::Internal::IRMutator*, std::allocator<Halide::Internal::IRMutator*> > const&)::$_0&) (__f=...) at /usr/bin/../lib64/gcc/x86_64-pc-linux-gnu/11.2.0/../../../../include/c++/11.2.0/bits/invoke.h:61
#12 0x00007fa432c080fd in std::__invoke_r<void, Halide::Internal::lower(std::vector<Halide::Internal::Function, std::allocator<Halide::Internal::Function> > const&, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, Halide::Target const&, std::vector<Halide::Argument, std::allocator<Halide::Argument> > const&, Halide::LinkageType, std::vector<Halide::Internal::Stmt, std::allocator<Halide::Internal::Stmt> > const&, bool, std::vector<Halide::Internal::IRMutator*, std::allocator<Halide::Internal::IRMutator*> > const&)::$_0&>(Halide::Internal::lower(std::vector<Halide::Internal::Function, std::allocator<Halide::Internal::Function> > const&, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, Halide::Target const&, std::vector<Halide::Argument, std::allocator<Halide::Argument> > const&, Halide::LinkageType, std::vector<Halide::Internal::Stmt, std::allocator<Halide::Internal::Stmt> > const&, bool, std::vector<Halide::Internal::IRMutator*, std::allocator<Halide::Internal::IRMutator*> > const&)::$_0&) (__fn=...) at /usr/bin/../lib64/gcc/x86_64-pc-linux-gnu/11.2.0/../../../../include/c++/11.2.0/bits/invoke.h:111
#13 0x00007fa432c07fcd in std::_Function_handler<void (), Halide::Internal::lower(std::vector<Halide::Internal::Function, std::allocator<Halide::Internal::Function> > const&, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, Halide::Target const&, std::vector<Halide::Argument, std::allocator<Halide::Argument> > const&, Halide::LinkageType, std::vector<Halide::Internal::Stmt, std::allocator<Halide::Internal::Stmt> > const&, bool, std::vector<Halide::Internal::IRMutator*, std::allocator<Halide::Internal::IRMutator*> > const&)::$_0>::_M_invoke(std::_Any_data const&) (__functor=...) at /usr/bin/../lib64/gcc/x86_64-pc-linux-gnu/11.2.0/../../../../include/c++/11.2.0/bits/std_function.h:291
#14 0x00007fa432c9a725 in std::function<void ()>::operator()() const (this=0x7fff64d856d0) at /usr/bin/../lib64/gcc/x86_64-pc-linux-gnu/11.2.0/../../../../include/c++/11.2.0/bits/std_function.h:560
#15 0x00007fa43385afac in Halide::Internal::run_with_large_stack(std::function<void ()> const&)::$_0::operator()() const (this=0x7fff64d85200) at Halide/src/Util.cpp:730
#16 0x00007fa43385af69 in Halide::Internal::run_with_large_stack(std::function<void ()> const&)::$_0::__invoke() () at Halide/src/Util.cpp:727
#17 0x00007fa437f066d0 in ?? () from /usr/lib/libc.so.6

After the fix

python reprod.py
Warning: It is meaningless to bound dimension v0 of function f to be within [0, 127] because the function is scheduled inline.
Warning: It is meaningless to bound dimension v0 of function f to be within [0, 127] because the function is scheduled inline.
Warning: It is meaningless to bound dimension v0 of function f to be within [0, 127] because the function is scheduled inline.

Process finished with exit code 0

[alexreinking]

This is now exactly halide_python_print(nullptr, msg);. Maybe you want to use that implementation?

[knzivid]

fixed

[steven-johnson]

I guess I should go read the guidelines on when acquiring/releasing the GIL is appropriate, since this is at least the second PR adding such a control...

[alexreinking]

Can you add this test case to python_bindings/correctness?

[knzivid]

@alexreinking Added a test to compare the warnings from stdout.

[knzivid]

Any idea what failed in this build?

https://buildbot.halide-lang.org/master/#builders/188/builds/47

[steven-johnson]

Any idea what failed in this build?

buildbot hiccups from being restarted this morning, should be restarted shortly