cvs commit: src/sys/kern kern_fork.c
alfred at freebsd.org
Wed Oct 24 19:34:28 PDT 2007
* David Xu <davidxu at FreeBSD.org> [071024 19:32] wrote:
> Alfred Perlstein wrote:
> >* 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
> >>>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
> >>>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.
> thread_suspend_check() with SINGLE_BOUNDARY is used is only called
> in userret() where I don't think any code is still using the p_fd.
This is not an acceptable solution as it will deadlock unless all
threads exit the kernel.
filedescs can be refcounted per thread I think.
- Alfred Perlstein
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