Random crashes with memory corruption symptoms

Ömer Sinan Ağacan omeragacan at gmail.com
Mon Feb 3 08:38:59 UTC 2020

In that case it'd be good to move the discussion to Gitlab. Could you file an

I was able to reproduce on GHC HEAD. With debug runtime I consistently get this
assertion error:

    internal error: ASSERTION FAILED: file rts/Messages.c, line 95

        (GHC version for x86_64_unknown_linux)
        Please report this as a GHC bug:  https://www.haskell.org/ghc/reportabug

In non-debug runtime it works fine maybe half of the time, in others I get a
panic in the GC.


Harendra Kumar <harendra.kumar at gmail.com>, 3 Şub 2020 Pzt, 10:01
tarihinde şunu yazdı:
> Unfortunately, it is present in 8.8.2 as well.
> On Mon, 3 Feb 2020 at 11:22, Ömer Sinan Ağacan <omeragacan at gmail.com> wrote:
>> You should try with 8.8.2 which fixes a bug in the compacting GC (#17088).
>> When debugging it's a good idea to use the latest minor release of your GHC
>> version (8.8.2 in your case), as minor releases fix bugs and usually do not
>> introduce new ones as they don't ship new features.
>> If the problem still exists, unless you're interested in GHC hacking I think
>> most productive use of the time would be to make the reproduer smaller, and
>> collect as many data as possible, like which flags trigger/hide the bug.
>> Some of the things you could check:
>> - Build your program with `-dcore-lint -dstg-lint -dcmm-lint` and see if it
>>   builds.
>> - Build your program with `-debug` and run it, see if it crahes.
>> - Build your program with `-debug` and run it with `+RTS -DS` and see if the
>>   error message changes.
>> But really you should try with 8.8.2 as first thing. It's possible that this is
>> another manifestation of #17088.
>> Ömer
>> Harendra Kumar <harendra.kumar at gmail.com>, 3 Şub 2020 Pzt, 01:26
>> tarihinde şunu yazdı:
>> >
>> > Hi,
>> >
>> > While running a test-suite for the streaming library streamly I am encountering a crash which seems to happen at random places at different times. The common messages are:
>> >
>> > * Segmentation fault: 11
>> > *  internal error: scavenge_mark_stack: unimplemented/strange closure type 24792696 @ 0x4200a623e0
>> > * internal error: update_fwd: unknown/strange object  223743520
>> >
>> > and several other such messages. Prima facie this looks like the memory is getting corrupted/scribbled somehow. My first suspicion was that this could be a problem in the streamly library code. But I have stripped down the code to bare minimum and there is no C FFI code or no poking to memory pointers.
>> >
>> > My next suspicion was the hspec/quickcheck testing code that is being used in this test. I checked the hspec code to ensure that there is no C code/pointer poking in any of the code involved. But no luck there as well, still looking to further strip down that code.
>> >
>> > My suspicion now is moving more towards the GHC RTS. This issue only shows when the following conditions are met:
>> >
>> > * hspec "parallel" combinator is used to run tests in parallel
>> > * streamly concurrent code is being tested which can create many threads
>> > * The GHC heap size is restricted to a small size ~32MB using "-M32M" rts option.
>> > * It is consistently seen with GHC 8.6.5 as well as GHC 8.8.1
>> >
>> > It never occurs when the heap size is not restricted. I have seen random crashes before as well with a "IO manager die" message, when using concurrent networking IO with streamly. Though earlier it was not easily reproducible, I stopped chasing it. But now it looks like that issue might also be a manifestation of the same underlying problem.
>> >
>> > My guess is it could be something in the RTS concurrency/threading related code. Let me know if the symptoms ring a bell or if you can point to something specific based on the symptoms. Also, what are the usual tools/methods/debugging aids/flags to debug such issues in GHC? If not a GHC issue what are the possible ways in which such problem can be induced by application code?
>> >
>> > Meanwhile, I am also trying to simplify the reproducing code further to remove other factors as much as possible. The current code is at https://github.com/composewell/streamly on the ghc-segfault branch. Run "$ while true; do cabal run properties || break; done" in the shell and if you are lucky it may crash soon. The test code is in "test/Prop.hs" - here https://github.com/composewell/streamly/blob/ghc-segfault/test/Prop.hs .
>> >
>> > -harendra
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