Simple "Hello World" Warp-based web server crashes on Ubuntu x86_64

Ben Gamari ben at
Tue Mar 1 15:53:38 UTC 2016

Антон Десятов <anton.dessiatov at> writes:

> Hello dear GHC developers,
> I have recently experienced what I believe to be a bug either in GHC or in
> Warp library (if it is indeed in Warp then sorry for posting to wrong
> mailing list). I've managed to shrink it to a few lines of code and publish
> on a GitHub. Here is the link:
> What I wanted to do is to establish network connection in my code and then
> at some point pass it to Warp for further processing. What I got is that
> after successfully processing first HTTP request my program consumes 100%
> CPU and eventually crashes with an error like this:
> *** Error in
> `/home/farnsworth/work/warp-ghc-issue/.stack-work/install/x86_64-linux/lts-5.5/7.10.3/bin/warp-ghc-issue':
> double free or corruption (!prev): 0x00000000016214b0 ***
> Aborted (core dumped)
> When compiled with -debug I see another message:
> repro: internal error: ASSERTION FAILED: file rts/Schedule.h, line 137
>     (GHC version 7.10.3 for x86_64_unknown_linux)
>     Please report this as a GHC bug:
> Aborted (core dumped)
> I tried to debug it by enabling -dcore-lint and -debug in my
> ~/.stack/config.yaml and what worries me is that in this case Warp itself
> doesn't compile (tried with 7.10.2 and 7.10.3) giving core lint failure in
> Network.Wai.Handler.Warp.HTTP2.Worker. Not sure if it is relevant, but
> looks suspicious.
This indeed quite relevant and concerning. Core lint issues should not
occur; they mean that somehow GHC has taken correct code (it
typechecked, afterall) and turned it into something horrible.

That being said, I'm afraid I can't reproduce this issue locally. What
warp version are you building against?

In the meantime, could you open a bug on the GHC Trac for this issue? It
would be quite helpful if you could attach the output from Core Lint
when you do so.


- Ben
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