linux-kernel - Re: [RFC PATCH 0/2] improve vmalloc allocation

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Message-ID: <20181023170532.GW18839@dhcp22.suse.cz>
Date:   Tue, 23 Oct 2018 19:05:32 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Shuah Khan <shuah@...nel.org>, Uladzislau Rezki <urezki@...il.com>,
        Kees Cook <keescook@...omium.org>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        LKML <linux-kernel@...r.kernel.org>,
        Thomas Garnier <thgarnie@...gle.com>,
        Oleksiy Avramchenko <oleksiy.avramchenko@...ymobile.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Joel Fernandes <joelaf@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...e.hu>, Tejun Heo <tj@...nel.org>
Subject: Re: [RFC PATCH 0/2] improve vmalloc allocation

On Tue 23-10-18 08:26:40, Matthew Wilcox wrote:
> On Tue, Oct 23, 2018 at 09:02:56AM -0600, Shuah Khan wrote:
[...]
> > The way it can be handled is by adding a test module under lib. test_kmod,
> > test_sysctl, test_user_copy etc.
> 
> The problem is that said module can only invoke functions which are
> exported using EXPORT_SYMBOL.  And there's a cost to exporting them,
> which I don't think we're willing to pay, purely to get test coverage.

Yes, I think we do not want to export internal functionality which might
be still interesting for the testing coverage. Maybe we want something
like EXPORT_SYMBOL_KSELFTEST which would allow to link within the
kselftest machinery but it wouldn't allow the same for general modules
and will not give any API promisses.

I wouldn't be surprised if we found some cases of EXPORT_SYMBOL* just to
make a symbol available for testing which would be unfortunate.
-- 
Michal Hocko
SUSE Labs