linux-kernel - Re: [PATCH v5 09/10] userfaultfd/selftests: reinitialize test context in each test

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Date:   Tue, 18 May 2021 15:28:52 -0700
From:   Axel Rasmussen <axelrasmussen@...gle.com>
To:     Peter Xu <peterx@...hat.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Hugh Dickins <hughd@...gle.com>,
        Jerome Glisse <jglisse@...hat.com>,
        Joe Perches <joe@...ches.com>,
        Lokesh Gidra <lokeshgidra@...gle.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        Shaohua Li <shli@...com>, Shuah Khan <shuah@...nel.org>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Wang Qing <wangqing@...o.com>, linux-api@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        linux-kselftest@...r.kernel.org, Linux MM <linux-mm@...ck.org>,
        Brian Geffon <bgeffon@...gle.com>,
        "Dr . David Alan Gilbert" <dgilbert@...hat.com>,
        Mina Almasry <almasrymina@...gle.com>,
        Oliver Upton <oupton@...gle.com>
Subject: Re: [PATCH v5 09/10] userfaultfd/selftests: reinitialize test context
 in each test

I suppose it will be squashed anyway, but in case it's useful feel free to add:

Reviewed-by: Axel Rasmussen <axelrasmussen@...gle.com>

Thanks for catching this, Peter!

On Tue, May 18, 2021 at 1:57 PM Peter Xu <peterx@...hat.com> wrote:
>
> On Tue, Apr 27, 2021 at 03:52:43PM -0700, Axel Rasmussen wrote:
> > Currently, the context (fds, mmap-ed areas, etc.) are global. Each test
> > mutates this state in some way, in some cases really "clobbering it"
> > (e.g., the events test mremap-ing area_dst over the top of area_src, or
> > the minor faults tests overwriting the count_verify values in the test
> > areas). We run the tests in a particular order, each test is careful to
> > make the right assumptions about its starting state, etc.
> >
> > But, this is fragile. It's better for a test's success or failure to not
> > depend on what some other prior test case did to the global state.
> >
> > To that end, clear and reinitialize the test context at the start of
> > each test case, so whatever prior test cases did doesn't affect future
> > tests.
> >
> > This is particularly relevant to this series because the events test's
> > mremap of area_dst screws up assumptions the minor fault test was
> > relying on. This wasn't a problem for hugetlb, as we don't mremap in
> > that case.
> >
> > Signed-off-by: Axel Rasmussen <axelrasmussen@...gle.com>
>
> Hi, Andrew,
>
> There's a conflict on the uffd test case with v5.13-rc1-mmots-2021-05-13-17-23
> between this patch and the uffd pagemap series, so I think we may need to queue
> another fixup patch (to be squashed into this patch of Axel's) which is
> attached.
>
> Thanks,
>
> --
> Peter Xu