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From Pedro Larroy <pedro.larroy.li...@gmail.com>
Subject Re: segmentation fault in master using mkdlnn
Date Thu, 03 May 2018 14:44:20 GMT
Looks like a problem in mkl's same_shape

the pointer to mkldnn::memory::desc &desc  looks invalid.

(More stack frames follow...)
(gdb) p desc
$1 = (const mkldnn::memory::desc &) @0x10: <error reading variable>
(gdb) p dtype
$2 = 0
(gdb) p shape
$3 = (const mxnet::TShape &) @0x7f3905a58b50: {<nnvm::Tuple<long>> =
{static kStackCache = <optimized out>, ndim_ = 2, num_heap_allocated_ = 0,
    data_stack_ = {20, 1, 139878025134112, 28}, data_heap_ = 0x0}, <No data
fields>}
(gdb)


On Thu, May 3, 2018 at 4:36 PM, Zheng, Da <dzzhen@amazon.com> wrote:

> There are a few problems with valgrind, which makes it not an ideal tool
> for mxnet with python interface.
>
> First, valgrind generates a huge number of irrelevant messages, most of
> them from in Python itself.
>
> Second, valgrind can't emulate all CPU instructions. I remember that when
> I run valgrind with mxnet, valgrind exits with a strange error. I later on
> found that it was caused by an unsupported CPU instructions.
>
> Third, valgrind doesn't support multithreading well. As far as I know,
> valgrind runs everything in a single thread even if the program uses
> multi-threading. An error like this, which is likely caused by race
> condition, can't be caught by valgrind.
>
> I used to use Address Sanitizer for memory errors. This tool is much
> faster and can work with multi-threads. However, it doesn't work with
> Python for some reason.
>
> One thing we potentially can do is to use memory checker for C++ unit
> tests. Not sure it'll cover all memory errors we want.
>
> Best,
> Da
>
> On 5/3/18, 6:50 AM, "Pedro Larroy" <pedro.larroy.lists@gmail.com> wrote:
>
>     It's very difficult to reproduce, non-deterministic. We were also
> running
>     without signal handlers in CI so there are no stack traces
> unfortunately.
>
>     Care to elaborate why valgrind doesn't work with Python?
>
>
>
>     On Thu, May 3, 2018 at 3:32 PM, Da Zheng <zhengda1936@gmail.com>
> wrote:
>
>     > can we build it in CI?segfault doesn't happen infrequently.
>     >
>     > 2018年5月2日 下午11:34,"Chris Olivier" <cjolivier01@gmail.com>写道:
>     >
>     > > you can try Intel Inspector, which is like an enhanced version of
>     > valgrind
>     > > with a GUI and whatnot.
>     > >
>     > > On Wed, May 2, 2018 at 9:42 PM Da Zheng <zhengda1936@gmail.com>
> wrote:
>     > >
>     > > > valgrind doesn't work with Python. also, valgrind doesn't
> support some
>     > > > CPU instructions used by MXNet (I think some instructions
> related to
>     > > > random generator).
>     > > >
>     > > >
>     > > > On Wed, May 2, 2018 at 8:59 PM, Bhavin Thaker <
> bhavinthaker@gmail.com>
>     > > > wrote:
>     > > > > Have you tried running with valgrind to get some clues on the
>     > > root-cause?
>     > > > >
>     > > > > Bhavin Thaker.
>     > > > >
>     > > > > On Wed, May 2, 2018 at 8:55 PM Da Zheng <zhengda1936@gmail.com
> >
>     > wrote:
>     > > > >
>     > > > >> It might also be possible that this isn't an MKLDNN bug.
>     > > > >> I just saw a similar memory error without MKLDNN build.
>     > > > >>
>     > > > >>
>     > > > http://jenkins.mxnet-ci.amazon-ml.com/blue/
> organizations/jenkins/
>     > > incubator-mxnet/detail/PR-10783/1/pipeline
>     > > > >>
>     > > > >> Best,
>     > > > >> Da
>     > > > >>
>     > > > >> On Wed, May 2, 2018 at 2:14 PM, Zheng, Da <dzzhen@amazon.com>
>     > wrote:
>     > > > >> > There might be a race condition that causes the memory
> error.
>     > > > >> > It might be caused by this PR:
>     > > > >> > https://github.com/apache/incubator-mxnet/pull/10706/files
>     > > > >> > This PR removes MKLDNN memory from NDArray.
>     > > > >> > However, I don't know why this causes memory error.
If
> someone is
>     > > > using
>     > > > >> the memory, it should still hold the memory with shared
> pointer.
>     > > > >> > But I do see the memory error increase after this PR
is
> merged.
>     > > > >> >
>     > > > >> > Best,
>     > > > >> > Da
>     > > > >> >
>     > > > >> > On 5/2/18, 12:26 PM, "Pedro Larroy" <
>     > pedro.larroy.lists@gmail.com>
>     > > > >> wrote:
>     > > > >> >
>     > > > >> >     I couldn't reproduce locally with:
>     > > > >> >
>     > > > >> >     ci/build.py -p ubuntu_cpu /work/runtime_functions.sh
>     > > > >> >     build_ubuntu_cpu_mkldnn && ci/build.py --platform
> ubuntu_cpu
>     > > > >> >     /work/runtime_functions.sh unittest_ubuntu_python2_cpu
>     > > > >> >
>     > > > >> >
>     > > > >> >     On Wed, May 2, 2018 at 8:50 PM, Pedro Larroy <
>     > > > >> pedro.larroy.lists@gmail.com>
>     > > > >> >     wrote:
>     > > > >> >
>     > > > >> >     > Hi
>     > > > >> >     >
>     > > > >> >     > Seems master is not running  anymore, there's
a
> segmentation
>     > > > fault
>     > > > >> using
>     > > > >> >     > MKDLNN-CPU
>     > > > >> >     >
>     > > > >> >     >
>     > > > http://jenkins.mxnet-ci.amazon-ml.com/blue/
> organizations/jenkins/
>     > > > >> >     > incubator-mxnet/detail/master/801/pipeline/662
>     > > > >> >     >
>     > > > >> >     >
>     > > > >> >     > I see my PRs failing with a similar error.
>     > > > >> >     >
>     > > > >> >     > Pedro
>     > > > >> >     >
>     > > > >> >
>     > > > >> >
>     > > > >>
>     > > >
>     > >
>     >
>
>
>

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