cvs commit: src/sys/kern kern_fork.c

[Alfred Perlstein]

* David Xu <davidxu at FreeBSD.org> [071024 18:34] wrote:
> Julian Elischer wrote:
> >julian      2007-10-23 17:54:16 UTC
> >
> >  FreeBSD src repository
> >
> >  Modified files:
> >    sys/kern             kern_fork.c 
> >  Log:
> >  Take out the single-threading code in fork.
> >  After discussions with jeff, alc, (various Ironport people), david Xu,
> >  and mostly Alfred (who found the problem) it has been demonstrated that 
> >  this
> >  is not needed for our implementations of threads and represents a real
> >  (as in we've seen it happen a lot) deadlock danger.
> >...
> 
> I think if process is forking a thread, that says flag RFPROC is not
> set and flags RFCFDG or RFCFDG is set, you still need to call
> thread_single(SINGLE_BOUNDARY), otherwise, for a threaded process,
> the memory pointed by p_fd is freed while other threads are using it,
> it will cause kernel to panic.

This is unlikely to be fixed by SINGLE_BOUNDARY and will likely require
refcounting to fix.  SINGLE_BOUNDARY will not fix the locations where
this happens:

        p = td->td_proc;
        fdp = p->p_fd;
        do something that blocks...
        re-use fdp.

-- 
- Alfred Perlstein