Random crashes with memory corruption symptoms

[Matthew Pickering]

The way to debug these kinds of issues is to use gdb.

The best clue in your message seems to be "The GHC heap size is
restricted to a small size ~32MB using "-M32M" rts option.".

Good luck!

Matt

On Sun, Feb 2, 2020 at 10:26 PM Harendra Kumar <harendra.kumar at gmail.com> wrote:
>
> 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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