Hi. In a program I have experienced a segmentation fault; not only that but also: * tpp.c:63: __pthread_tpp_change_priority: Assertion `new_prio == -1 || (new_prio >= __sched_fifo_min_prio && new_prio <= __sched_fifo_max_prio)' failed. * internal error: removeThreadFromQueue: not found (GHC version 6.8.2 for i386_unknown_linux) Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug I have managed to write a program that reproduces the problem: http://hpaste.org/fastcgi/hpaste.fcgi/view?id=3714 Compile with: $ghc --make -threaded -O2 main.hs Execute with: $./main +RTS -A128M -s -c -N4 -RTS 5000000 500 This should produce a segmentation fault (or one of the previous errors). I strongly suspect that the cause is an uncaught stack overflow. Executing the code with only 1 threads, there are no more problems. Increasing the thread stack size (-k1M), there are no more problems. If the problem is really an uncaught stack overflow, I'm rather sure that a more simple test can be written, to reproduce the problem. I'm on Linux Debian Etch i386; GHC 6.8.2. Some notes about the program: - when no segmentation fault occurs, the program requires about 1 GB of memory - there is no real parallelization, only 1 CPU is used - the mapReduce implementation is taken from Real World Haskell - the code is adapted from the code I'm using in a project Thanks Manlio Perillo