[Valgrind-developers] how can this ever work?

[Paul M. <pa...@sa...>]

I'm getting assertion failures in sema_down and sema_up in
coregrind/linux/sema.c in valgrind-2.4.0.  Since core_os.h defines
FUTEX_SEMA to 0, we are using the pipe-based semaphores, not the
futex-based ones.  (Why? do the futex-based ones not work?)

Looking at sema_up/down, I can't see how it can possibly work
correctly in the presence of fork().  If the client does a fork(), we
do a fork() too, while holding the semaphore.  The parent and all its
descendents end up using the same pipe (assuming they don't do an
execv*), and after a fork, both parent and child will think they hold
the token and are entitled to do an up.  Consequently we can end up
with lots of tokens in the pipe (and I see that happening).

What was the intention here?  How was this supposed to work?

This is on PPC, but this problem isn't PPC-specific AFAICS.

Paul.