[dm-devel] dm: fix iterate_device sanity check

[Mike Snitzer]

On Mon, Feb 01 2021 at 10:35pm -0500,
Jeffle Xu <jefflexu at linux.alibaba.com> wrote:

> According to the definition of dm_iterate_devices_fn:
>  * This function must iterate through each section of device used by the
>  * target until it encounters a non-zero return code, which it then returns.
>  * Returns zero if no callout returned non-zero.
> 
> For some target type (e.g., dm-stripe), one call of iterate_devices() may
> iterate multiple underlying devices internally, in which case a non-zero
> return code returned by iterate_devices_callout_fn will stop the iteration
> in advance.
> 
> Thus if we want to ensure that _all_ underlying devices support some kind of
> attribute, the iteration structure like dm_table_supports_nowait() should be
> used, while the input iterate_devices_callout_fn should handle the 'not
> support' semantics. On the opposite, the iteration structure like
> dm_table_any_device_attribute() should be used if _any_ underlying device
> supporting this attibute is sufficient. In this case, the input
> iterate_devices_callout_fn should handle the 'support' semantics.
> 
> Fixes: 545ed20e6df6 ("dm: add infrastructure for DAX support")
> Fixes: c3c4555edd10 ("dm table: clear add_random unless all devices have it set")
> Fixes: 4693c9668fdc ("dm table: propagate non rotational flag")
> Cc: stable at vger.kernel.org
> Signed-off-by: Jeffle Xu <jefflexu at linux.alibaba.com>

Thanks for auditing and fixing this up.  It has been on my todo so
you've really helped me out -- your changes look correct to me.

I've staged it for 5.12, the stable fix will likely need manual fixups
depending on the stable tree... we'll just need to assist with
backport(s) as needed.

Thanks again,
Mike