Hi,

On Thu, Sep 5, 2013 at 9:10 PM, Kazu Yamamoto <kazu@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