Re: Fixing UML against NPTL (was: Re: [uml-devel] [PATCH] UML: Use PTRACE_KILL instead of SIGKILL to kill host-OS processes (take #2))

Blaisorblade
2004-11-12T00:35:28Z

On Thursday 11 November 2004 19:45, Daniel Jacobowitz wrote:
> On Thu, Nov 11, 2004 at 07:31:51PM +0100, Christophe Saout wrote:
> > Am Donnerstag, den 11.11.2004, 12:45 -0500 schrieb Daniel Jacobowitz:
> > > Glibc caches the PID. If you're going to use clone directly, use the
> > > gettid/getpid syscall directly. It's kind of rude that glibc breaks
> > > getpid in this way; I recommend filing a bug in the glibc bugzilla at
> > > sources.redhat.com.
>
> ... but, thinking about it, they'll probably close it as INVALID.
>
> > If glibc insists on caching the pid, it could also simply invalidate the
> > pid cache in the clone function.

> It currently does this for vfork, but not clone. Basically, you can't
> call into glibc at all if you use clone. If you aren't using POSIX
> threads, then the POSIX-compliant library is going to fall to pieces
> around you. For instance, all the file locking will break, and
> anything else that, like the PID cache, relies on either global or
> per-_thread_ data.

Yes, in fact I guess that the problem is for any _thread variable. And as
fork() is not a raw syscall, so clone() shouldn't be.

I'll file a bugreport when I have time to do it properly - I don't want to
hear that "if I go into dirty things using clone(), I get to keep the pieces
and setup a different TLS for the new process"
--
Paolo Giarrusso, aka Blaisorblade
Linux registered user n. 292729