Re: [PATCH 2/2] of: some unittest overlays not untracked

Geert Uytterhoeven
2020-03-26T08:22:08Z

Hi Frank,

On Thu, Mar 26, 2020 at 2:47 AM <frowand.list@gmail.com> wrote:
> From: Frank Rowand <frank.rowand@sony.com>
>
> kernel test robot reported "WARNING: held lock freed!" triggered by
> unittest_gpio_remove(), which should not have been called because
> the related gpio overlay was not tracked. Another overlay that
> was tracked had previously used the same id as the gpio overlay
> but had not been untracked when the overlay was removed. Thus the
> clean up function of_unittest_destroy_tracked_overlays() incorrectly
> attempted to remove the reused overlay id.
>
> Patch contents:
>
> - Create tracking related helper functions
> - Change BUG() to WARN_ON() for overlay id related issues
> - Add some additional error checking for valid overlay id values
> - Add the missing overlay untrack
> - update comment on expectation that overlay ids are assigned in
> sequence
>
> Fixes: 492a22aceb75 ("of: unittest: overlay: Keep track of created overlays")
> Reported-by: kernel test robot <lkp@intel.com>
> Signed-off-by: Frank Rowand <frank.rowand@sony.com>

Looks good to me, so:
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>

Still, a few suggestions for future improvement below...

> --- a/drivers/of/unittest.c
> +++ b/drivers/of/unittest.c
> @@ -1689,19 +1689,27 @@ static const char *overlay_name_from_nr(int nr)
>
> static const char *bus_path = "/testcase-data/overlay-node/test-bus";
>
> -/* it is guaranteed that overlay ids are assigned in sequence */
> +/* FIXME: it is NOT guaranteed that overlay ids are assigned in sequence */
> +
> #define MAX_UNITTEST_OVERLAYS 256
> static unsigned long overlay_id_bits[BITS_TO_LONGS(MAX_UNITTEST_OVERLAYS)];

Obviously this should have used DECLARE_BITMAP() ;-)

> static int overlay_first_id = -1;
>
> +static long of_unittest_overlay_tracked(int id)
> +{
> + if (WARN_ON(id >= MAX_UNITTEST_OVERLAYS))
> + return 0;

Do we need all these checks on id? Can this really happen?
I guess doing it once in of_unittest_track_overlay(), and aborting all
of_unittests if it triggers should be sufficient?

> + return overlay_id_bits[BIT_WORD(id)] & BIT_MASK(id);

No need for BIT_{WORD,MASK}() calculations if you would use test_bit().

> +}
> +
> static void of_unittest_track_overlay(int id)
> {
> if (overlay_first_id < 0)
> overlay_first_id = id;
> id -= overlay_first_id;
>
> - /* we shouldn't need that many */
> - BUG_ON(id >= MAX_UNITTEST_OVERLAYS);
> + if (WARN_ON(id >= MAX_UNITTEST_OVERLAYS))
> + return;
> overlay_id_bits[BIT_WORD(id)] |= BIT_MASK(id);

set_bit()

> }
>
> @@ -1710,7 +1718,8 @@ static void of_unittest_untrack_overlay(int id)
> if (overlay_first_id < 0)
> return;
> id -= overlay_first_id;
> - BUG_ON(id >= MAX_UNITTEST_OVERLAYS);
> + if (WARN_ON(id >= MAX_UNITTEST_OVERLAYS))
> + return;
> overlay_id_bits[BIT_WORD(id)] &= ~BIT_MASK(id);

clear_bit()

> }
>
> @@ -1726,7 +1735,7 @@ static void of_unittest_destroy_tracked_overlays(void)
> defers = 0;
> /* remove in reverse order */

If it is not guaranteed that overlay ids are assigned in sequence, the
reverse order is not really needed, so you could replace the bitmap and
your own tracking mechanism by DEFINE_IDR() and idr_for_each()?
And as IDRs are flexible, MAX_UNITTEST_OVERLAYS and all checks
could be removed, too.

> for (id = MAX_UNITTEST_OVERLAYS - 1; id >= 0; id--) {
> - if (!(overlay_id_bits[BIT_WORD(id)] & BIT_MASK(id)))
> + if (!of_unittest_overlay_tracked(id))
> continue;
>
> ovcs_id = id + overlay_first_id;
> @@ -1743,7 +1752,7 @@ static void of_unittest_destroy_tracked_overlays(void)
> continue;
> }
>
> - overlay_id_bits[BIT_WORD(id)] &= ~BIT_MASK(id);
> + of_unittest_untrack_overlay(id);
> }
> } while (defers > 0);
> }

Gr{oetje,eeting}s,

Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds