linux-kernel - Re: [PATCH v2 7/9] userfaultfd/selftests: reinitialize test context in each test

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Date:   Tue, 13 Apr 2021 16:15:35 -0400
From:   Peter Xu <peterx@...hat.com>
To:     Axel Rasmussen <axelrasmussen@...gle.com>
Cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        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, linux-kernel@...r.kernel.org,
        linux-kselftest@...r.kernel.org, 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 v2 7/9] userfaultfd/selftests: reinitialize test context
 in each test

On Mon, Apr 12, 2021 at 10:17:19PM -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>
> ---
>  tools/testing/selftests/vm/userfaultfd.c | 221 +++++++++++++----------
>  1 file changed, 127 insertions(+), 94 deletions(-)
> 
> diff --git a/tools/testing/selftests/vm/userfaultfd.c b/tools/testing/selftests/vm/userfaultfd.c
> index 1f65c4ab7994..0ff01f437a39 100644
> --- a/tools/testing/selftests/vm/userfaultfd.c
> +++ b/tools/testing/selftests/vm/userfaultfd.c
> @@ -89,7 +89,8 @@ static int shm_fd;
>  static int huge_fd;
>  static char *huge_fd_off0;
>  static unsigned long long *count_verify;
> -static int uffd, uffd_flags, finished, *pipefd;
> +static int uffd = -1;
> +static int uffd_flags, finished, *pipefd;
>  static char *area_src, *area_src_alias, *area_dst, *area_dst_alias;
>  static char *zeropage;
>  pthread_attr_t attr;
> @@ -342,6 +343,121 @@ static struct uffd_test_ops hugetlb_uffd_test_ops = {
>  
>  static struct uffd_test_ops *uffd_test_ops;
>  
> +static int userfaultfd_open(uint64_t *features)
> +{
> +	struct uffdio_api uffdio_api;
> +
> +	uffd = syscall(__NR_userfaultfd, O_CLOEXEC | O_NONBLOCK);

Keep UFFD_USER_MODE_ONLY?

[...]

> @@ -961,10 +1045,9 @@ static int userfaultfd_zeropage_test(void)
>  	printf("testing UFFDIO_ZEROPAGE: ");
>  	fflush(stdout);
>  
> -	uffd_test_ops->release_pages(area_dst);
> -
> -	if (userfaultfd_open(0))
> +	if (uffd_test_ctx_clear() || uffd_test_ctx_init(0))
>  		return 1;

Would it look even nicer to init() at the entry of each test, and clear() after
finish one test?

> +
>  	uffdio_register.range.start = (unsigned long) area_dst;
>  	uffdio_register.range.len = nr_pages * page_size;
>  	uffdio_register.mode = UFFDIO_REGISTER_MODE_MISSING;

The rest looks good to me.  Thanks,

-- 
Peter Xu