Re: [PATCH v5 5/8] virtio: Treat alloc_dax() -EOPNOTSUPP failure as non-fatal

[Linus Torvalds]

On Mon, 12 Feb 2024 at 14:04, Dan Williams <dan.j.williams@xxxxxxxxx> wrote:
>
> This works because the internals of virtio_fs_cleanup_dax(), "kill_dax()
> and put_dax()", know how to handle a NULL @dax_dev. It is still early
> days with the "cleanup" helpers, but I wonder if anyone else cares that
> the DEFINE_FREE() above does not check for NULL?

Well, the main reason for DEFINE_FREE() to check for NULL is not
correctness, but code generation. See the comment about kfree() in
<linux/cleanup.h>:

 * NOTE: the DEFINE_FREE()'s @free expression includes a NULL test even though
 * kfree() is fine to be called with a NULL value. This is on purpose. This way
 * the compiler sees the end of our alloc_obj() function as [...]

with the full explanation there.

Now, whether the code wants to actually use the cleanup() helpers for
a single use-case is debatable.

But yes, if it does, I suspect it should use !IS_ERR_OR_NULL(ptr).

            Linus