A bug of multicore IO manager

[Akio Takano]

Hi,

On Thu, Sep 5, 2013 at 9:10 PM, Kazu Yamamoto <kazu at iij.ad.jp> wrote:

> Hi,
>
> > If you need two Ctrl-Cs to kill the program, it probably means that it
> > deadlocked somewhere, maybe in the RTS.  Kazu: if you can attach to
> > the deadlocked process with gdb and get stack traces of all the
> > threads, that might help.
>
> To debug with GDB, I complied Mighty with "-debug". This changes the
> behavior and I got the following error:
>
> mighty-20130905: internal error: ASSERTION FAILED: file rts/sm/MarkWeak.c,
> line 371
>
>     (GHC version 7.7.20130901 for i386_unknown_linux)
>     Please report this as a GHC bug:
> http://www.haskell.org/ghc/reportabug
>

I wonder if this issue could have been introduced by the commit:

https://github.com/ghc/ghc/commit/6770663f764db76dbb7138ccb3aea0527d194151

It looks like after the commit, addCFinalizerToWeak# can call into the GC
with the closure lock held. This means the info pointer points to
stg_WHITEHOLE_info, breaking the asserted invariant. I haven't done any
testing to confirm this, however.

-- Takano Akio
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