Incubator-mxnet: Floating point exception in mxnet.ndarray.op.random_pdf_poisson

[leeyeetonn]

Description

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mxnet.ndarray.op.random_pdf_poisson has floating point exception when given lam is shape (0,). Please see the provided code snippet for example.

Error Message

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Floating point exception (core dumped)

To Reproduce

(If you developed your own code, please provide a short script that reproduces the error. For existing examples, please provide link.)

import mxnet
import numpy as np
lam = mxnet.nd.array(np.random.rand(0))
sample = mxnet.nd.array(np.random.rand(2))
mxnet.ndarray.op.random_pdf_poisson(sample=sample, lam=lam)

Steps to reproduce

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1. run the provided code in python interpreter or as a script
   2.

What have you tried to solve it?

1.
2.

Environment

We recommend using our script for collecting the diagnositc information. Run the following command and paste the outputs below:

curl --retry 10 -s https://raw.githubusercontent.com/dmlc/gluon-nlp/master/tools/diagnose.py | python

# paste outputs here

Got 404 when trying to get the script.

Some environment information:

• OS: ubuntu 18.04
• Python: 3.7.6
• pip: 20.0.2
• numpy: 1.18.5
• mxnet: 1.6.0

[szha]

Here's the problem:

% DMLC_LOG_STACK_TRACE_DEPTH=150 MXNET_ENGINE_TYPE=NaiveEngine lldb python3.7 -- test_18937.py
(lldb) target create "python3.7"
Current executable set to 'python3.7' (x86_64).
(lldb) settings set -- target.run-args  "test_18937.py"
(lldb) run
Process 36591 launched: '/usr/local/bin/python3.7' (x86_64)
Process 36591 stopped
* thread #2, stop reason = exec
    frame #0: 0x0000000100006000 dyld`_dyld_start
dyld`_dyld_start:
->  0x100006000 <+0>: popq   %rdi
    0x100006001 <+1>: pushq  $0x0
    0x100006003 <+3>: movq   %rsp, %rbp
    0x100006006 <+6>: andq   $-0x10, %rsp
(lldb) cont
Process 36591 resuming
[23:22:22] ../src/engine/engine.cc:55: MXNet start using engine: NaiveEngine
[23:22:22] ../src/storage/storage.cc:198: Using Pooled (Naive) StorageManager for CPU
Process 36591 stopped
* thread #2, queue = 'com.apple.main-thread', stop reason = EXC_ARITHMETIC (code=EXC_I386_DIV, subcode=0x0)
    frame #0: 0x0000000115bca540 libmxnet.dylib`mxnet::op::PdfCaller<mshadow::cpu, float, mxnet::op::PDF_Poisson<false>, 1, false>::op(inputs=0x00007ffeefbfcb50, outputs=0x00007ffeefbfcb30, s=0x00000001272d39c9) at pdf_op.h:469
   466    static void op(const std::vector<TBlob>& inputs,
   467                   const std::vector<TBlob>& outputs,
   468                   mshadow::Stream<xpu> *s) {
-> 469      CHECK_EQ(inputs[0].Size()%inputs[1].Size(), 0);
   470      CHECK_EQ(inputs[0].Size()%outputs[0].Size(), 0);
   471      index_t num_samples(inputs[0].Size() / inputs[1].Size());
   472      mxnet_op::Kernel<LaunchExWrapper<pdf>, xpu>::LaunchEx(s, outputs[0].Size(), num_samples,

https://github.com/apache/incubator-mxnet/blob/9bdd4d6347c284770ee5bfe5ae98f1dabc283829/src/operator/random/pdf_op.h#L469

The code needs to guard against zero-size array for right operand of %, and we should add a smoke test to guard against such problem in this op, similar to https://github.com/apache/incubator-mxnet/pull/18972/files.

[szha]

@xidulu same question as https://github.com/apache/incubator-mxnet/issues/18936#issuecomment-678064250, since we are deprecating ndarray in favor of np/npx, do we need to register an alias of this op in np/npx? (or is it already registered)

[xidulu]

@szha
As far as I am concerned, pdf ops are not registered under npx yet and I don't think its that necessary because:

1. This series of ops do not have very good support for numpy's broadcasting and zero-dim/size (as is shown in this issue) semantics, which could cause great confusion for users.
2. Secondly, if users would have access to pdf ops, they could now use the pdf operator inside the probability module.

[xidulu]

Btw, a possible solution for this bug could be adding a zero-size check (e.g. https://github.com/apache/incubator-mxnet/blob/master/src/operator/numpy/random/np_normal_op.h#L320) before the kernel launch: https://github.com/apache/incubator-mxnet/blob/master/src/operator/random/pdf_op.h#L514