Re: [RFC PATCH 1/1] vmalloc: add test driver to analyse vmalloc allocator

[Michal Hocko <mhocko@kernel.org>]

On Tue 13-11-18 14:10:46, Andrew Morton wrote:
[...]
> > +static int vmalloc_test_init(void)
> > +{
> > +	__my_vmalloc_node_range =
> > +		(void *) kallsyms_lookup_name("__vmalloc_node_range");
> > +
> > +	if (__my_vmalloc_node_range)
> > +		do_concurrent_test();
> > +
> > +	return -EAGAIN; /* Fail will directly unload the module */
> > +}
> 
> It's unclear why this module needs access to the internal
> __vmalloc_node_range().  Please fully explain this in the changelog.
> 
> Then, let's just export the thing.  (I expect this module needs a
> Kconfig dependency on CONFIG_KALLSYMS, btw).  A suitable way of doing
> that would be
> 
> /* Exported for lib/test_vmalloc.c.  Please do not use elsewhere */
> EXPORT_SYMBOL_GPL(__vmalloc_node_range);

There was a previous discussion that testing for internal infrastructure
is useful quite often and such a testing module needs an access to such
an internal infrastructure. Exporting those symbols via standard
EXPORT_SYMBOL_GPL is far from optimal because we can be pretty much sure
an abuse will arise sooner than later. I was proposing
EXPORT_SYMBOL_SELFTEST that would link only against testing modules.

If that is not viable for some reason then kallsyms_lookup_name is a
dirty-but-usable workaround.
-- 
Michal Hocko
SUSE Labs