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Date:   Wed, 28 Apr 2021 13:23:41 -0400
From:   Peter Xu <peterx@redhat.com>
To:     Axel Rasmussen <axelrasmussen@google.com>
Cc:     Alexander Viro <viro@zeniv.linux.org.uk>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Hugh Dickins <hughd@google.com>,
        Jerome Glisse <jglisse@redhat.com>,
        Joe Perches <joe@perches.com>,
        Lokesh Gidra <lokeshgidra@google.com>,
        Mike Kravetz <mike.kravetz@oracle.com>,
        Mike Rapoport <rppt@linux.vnet.ibm.com>,
        Shaohua Li <shli@fb.com>, Shuah Khan <shuah@kernel.org>,
        Stephen Rothwell <sfr@canb.auug.org.au>,
        Wang Qing <wangqing@vivo.com>, linux-api@vger.kernel.org,
        linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-kselftest@vger.kernel.org, linux-mm@kvack.org,
        Brian Geffon <bgeffon@google.com>,
        "Dr . David Alan Gilbert" <dgilbert@redhat.com>,
        Mina Almasry <almasrymina@google.com>,
        Oliver Upton <oupton@google.com>
Subject: Re: [PATCH v5 09/10] userfaultfd/selftests: reinitialize test
 context in each test
Message-ID: <20210428172341.GF6584@xz-x1>
References: <20210427225244.4326-1-axelrasmussen@google.com>
 <20210427225244.4326-10-axelrasmussen@google.com>
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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@google.com>

Reviewed-by: Peter Xu <peterx@redhat.com>

-- 
Peter Xu