libc using pthread routines (was nss_ldap broken)

On Fri, 2004-03-26 at 13:16, Sean McNeil wrote:
> On Fri, 2004-03-26 at 13:00, Sean McNeil wrote:
> > OK, I think I understand this problem...
> > 
> > When I have my nsswitch.conf setup as follows, I get seg11s:
> > 
> > passwd: files ldap
> > group: files ldap
> > 
> > This appears to be an issue with any external nss_*.so.1 module that
> > uses pthread.  It looks to me it is about the following:
> > 
> > /*
> >  * Cleanup
> >  */
> > static void
> > nss_atexit(void)
> > {
> > 	(void)_pthread_rwlock_wrlock(&nss_lock);
> > 	VECTOR_FREE(_nsmap, &_nsmapsize, sizeof(*_nsmap),
> > 	    (vector_free_elem)ns_dbt_free);
> > 	VECTOR_FREE(_nsmod, &_nsmodsize, sizeof(*_nsmod),
> > 	    (vector_free_elem)ns_mod_free);
> > 	(void)_pthread_rwlock_unlock(&nss_lock);
> > }
> > 
> > In my case, the nss_ldap.so.1 module was loaded which pulls in
> > libpthread.  I'm not sure how this works without a libpthred, but it
> > would appear that unless libpthread.so is loaded everything is OK.  But
> > now, it has been loaded and the rwlock_wrlock() works, but then it has
> > been unloaded before rwlock_unlock() gets called.
> > 
> > Would using
> > 
> > #include <reentrant.h>
> > rwlock_wrlock()
> > rwlock_unlock()
> > 
> > macros fix this?
> > 
> > Cheers,
> > Sean
> > 
> 
> Final thought:  exit() sets __isthreaded to 0, so I am hazarding a guess
> that the lock isn't necessary.  Removing the lock/unlock from
> nss_atexit() did the trick.
> 
> Sean
> 

I was looking at this wrong. __isthreaded is set to 0 as an initializer,
so I guess there is a need to lock and unlock in the atexit routine.

I am very puzzled about these routines. net/nsdispatch.c is the only
file in libc that uses the _pthread_ routines directly.  Others use the
macros that test __isthreaded.  The macros, however, will not provide
the status of the call back.  The most peculiar thing about it all is I
cannot see how these are resolved if no thread library is loaded.

 How does this mechanism work?  I see that the routines in question are
marked as "W" by nm.  So if a thread library doesn't get loaded in this
routine resolves to 0?  And a call to 0 returns ok?  Can someone help
out this confused soul?

Sean