Random crashes with memory corruption symptoms

Mon Feb 3 09:35:14 UTC 2020

> Did you try it on the code I sent or did you use some other test case?

I tried your code.

It's still possible that this is an application bug, of course (maybe in one of
the dependencies, if not in your application).

> Is there a test-suite in GHC that stresses the threaded runtime?

Some of the tests in the test suite uses threaded runtime. Other than those not
really.

Ömer

Harendra Kumar <harendra.kumar at gmail.com>, 3 Şub 2020 Pzt, 12:29
tarihinde şunu yazdı:
>
> 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
>> >> > _______________________________________________
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