Re: [PATCH 5.13 191/223] selftest: use mmap instead of posix_memalign to allocate memory

[Peter Collingbourne]

On Mon, Jul 26, 2021 at 9:16 AM Greg Kroah-Hartman
<gregkh@xxxxxxxxxxxxxxxxxxx> wrote:
>
> From: Peter Collingbourne <pcc@xxxxxxxxxx>
>
> commit 0db282ba2c12c1515d490d14a1ff696643ab0f1b upstream.
>
> This test passes pointers obtained from anon_allocate_area to the
> userfaultfd and mremap APIs.  This causes a problem if the system
> allocator returns tagged pointers because with the tagged address ABI
> the kernel rejects tagged addresses passed to these APIs, which would
> end up causing the test to fail.  To make this test compatible with such
> system allocators, stop using the system allocator to allocate memory in
> anon_allocate_area, and instead just use mmap.
>
> Link: https://lkml.kernel.org/r/20210714195437.118982-3-pcc@xxxxxxxxxx
> Link: https://linux-review.googlesource.com/id/Icac91064fcd923f77a83e8e133f8631c5b8fc241
> Fixes: c47174fc362a ("userfaultfd: selftest")
> Co-developed-by: Lokesh Gidra <lokeshgidra@xxxxxxxxxx>
> Signed-off-by: Lokesh Gidra <lokeshgidra@xxxxxxxxxx>
> Signed-off-by: Peter Collingbourne <pcc@xxxxxxxxxx>
> Reviewed-by: Catalin Marinas <catalin.marinas@xxxxxxx>
> Cc: Vincenzo Frascino <vincenzo.frascino@xxxxxxx>
> Cc: Dave Martin <Dave.Martin@xxxxxxx>
> Cc: Will Deacon <will@xxxxxxxxxx>
> Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
> Cc: Alistair Delva <adelva@xxxxxxxxxx>
> Cc: William McVicker <willmcvicker@xxxxxxxxxx>
> Cc: Evgenii Stepanov <eugenis@xxxxxxxxxx>
> Cc: Mitch Phillips <mitchp@xxxxxxxxxx>
> Cc: Andrey Konovalov <andreyknvl@xxxxxxxxx>
> Cc: <stable@xxxxxxxxxxxxxxx>    [5.4]
> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> ---
>  tools/testing/selftests/vm/userfaultfd.c |    6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
>
> --- a/tools/testing/selftests/vm/userfaultfd.c
> +++ b/tools/testing/selftests/vm/userfaultfd.c
> @@ -197,8 +197,10 @@ static int anon_release_pages(char *rel_
>
>  static void anon_allocate_area(void **alloc_area)
>  {
> -       if (posix_memalign(alloc_area, page_size, nr_pages * page_size)) {
> -               fprintf(stderr, "out of memory\n");
> +       *alloc_area = mmap(NULL, nr_pages * page_size, PROT_READ | PROT_WRITE,
> +                          MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
> +       if (*alloc_area == MAP_FAILED)

Hi Greg,

It looks like your backport of this patch (and the backports to stable
kernels) are missing a left brace here.

Peter

> +               fprintf(stderr, "mmap of anonymous memory failed");
>                 *alloc_area = NULL;
>         }
>  }
>
>