On Sun, Jul 24, 2016 at 10:50 AM Lana Black <lanablack@amok.cc> wrote:

Hello,

I have run into this RTS bug recently. In short, when executing multiple
consequtive forks, after 500-600 or so the process is terminated by
SIGSEGV. I know this kind of thing is totally artificial, but still.

The problem I have is that I can't get any meaningful backtrace in gdb.
For example, for threaded RTS I get this

(gdb) bt
#0 0x0000000000560d63 in
base_GHCziEventziThread_ensureIOManagerIsRunning1_info ()
Backtrace stopped: Cannot access memory at address 0x7fffff7fcea0

For non-threaded RTS I get this

(gdb) bt
#0 0x00000000007138c9 in stg_makeStablePtrzh ()
Backtrace stopped: Cannot access memory at address 0x7fffff7fc720

Build command: ghc --make -O2 -g -fforce-recomp fork.hs
Add threaded if needed.

I was able to reproduce this bug with both GHC 7.10.3 and todays HEAD
with the code below.

>import System.Exit (exitSuccess)
>import System.Posix.Process (forkProcess)
>
>fork_ n | n > 0 = processPid =<< forkProcess (fork_ $! n - 1)
> | otherwise = putStrLn "I'm done!"
>
>processPid pid | pid > 0 = exitSuccess
> | pid < 0 = putStrLn "OOOPS, forkProcess failed!"
> | otherwise = pure ()
>
>main = fork_ 1000
>

With best regards.
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