From: Andrew Morton <akpm@linux-foundation.org>
To: Michal Hocko <mhocko@kernel.org>
Cc: "Uladzislau Rezki (Sony)" <urezki@gmail.com>,
Kees Cook <keescook@chromium.org>, Shuah Khan <shuah@kernel.org>,
linux-mm@kvack.org, LKML <linux-kernel@vger.kernel.org>,
Matthew Wilcox <willy@infradead.org>,
Oleksiy Avramchenko <oleksiy.avramchenko@sonymobile.com>,
Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [RFC PATCH 1/1] vmalloc: add test driver to analyse vmalloc allocator
Date: Wed, 14 Nov 2018 15:00:53 -0800 [thread overview]
Message-ID: <20181114150053.c3fe42507923322a0a10ae1c@linux-foundation.org> (raw)
In-Reply-To: <20181114151737.GA23419@dhcp22.suse.cz>
On Wed, 14 Nov 2018 16:17:37 +0100 Michal Hocko <mhocko@kernel.org> wrote:
> 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.
That's rather overdoing things, I think. If someone uses a
dont-use-this symbol then they get to own both pieces when it breaks.
We could simply do
#define EXPORT_SYMBOL_SELFTEST EXPORT_SYMBOL_GPL
then write a script which checks the tree for usages of the
thus-tagged symbols outside tools/testing and lib/ (?)
> If that is not viable for some reason then kallsyms_lookup_name is a
> dirty-but-usable workaround.
Well yes. It adds a dependency on CONFIG_KALLSYMS and will cause
silent breakage if __vmalloc_node_range gets renamed, has its arguments
changed, etc.
next prev parent reply other threads:[~2018-11-14 23:00 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-13 15:16 [RFC PATCH 0/1] test driver to analyse vmalloc allocator Uladzislau Rezki (Sony)
2018-11-13 15:16 ` [RFC PATCH 1/1] vmalloc: add " Uladzislau Rezki (Sony)
2018-11-13 22:10 ` Andrew Morton
2018-11-14 15:17 ` Michal Hocko
2018-11-14 23:00 ` Andrew Morton [this message]
2018-11-15 8:39 ` Michal Hocko
2018-11-15 8:46 ` Matthew Wilcox
2018-11-15 12:57 ` Michal Hocko
2018-11-15 13:47 ` Matthew Wilcox
2018-11-15 20:57 ` Andrew Morton
2018-11-15 12:36 ` Uladzislau Rezki
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