Random crashes with memory corruption symptoms

Mon Feb 3 09:29:40 UTC 2020

Ok, I will file an issue. I just wanted to rule out any application level
issues first. Did you try it on the code I sent or did you use some other
test case? Is there a test-suite in GHC that stresses the threaded runtime?

-harendra

On Mon, 3 Feb 2020 at 14:09, Ömer Sinan Ağacan <omeragacan at gmail.com> wrote:

> In that case it'd be good to move the discussion to Gitlab. Could you file
> an
> issue?
>
> 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 8.11.0.20200201 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.
>
> Ömer
>
> 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
> >> > _______________________________________________
> >> > ghc-devs mailing list
> >> > ghc-devs at haskell.org
> >> > http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs
>
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