Re: [PATCH] iov_iter: separate direction from flavour

[Matthew Wilcox]

On Sun, Jul 04, 2021 at 03:44:17PM -0700, Linus Torvalds wrote:
> On Sun, Jul 4, 2021 at 2:47 PM Guenter Roeck <linux@xxxxxxxxxxxx> wrote:
> >
> > How about the following ?
> >
> >         WARN_ON_ONCE(IS_ENABLED(CONFIG_MMU) && uaccess_kernel());
> 
> Nope, that doesn't work either, because there are no-MMU setups that
> don't make the same mistake no-mmu arm and m68k do.
> 
> Example: xtensa. But afaik also generic-asm/uaccess.h unless the
> architecture overrides something.
> 
> So this literally seems like just an arm/m68k bug.

We could slip:

#ifndef uaccess_user
#define uaccess_user() !uaccess_kernel()
#endif

into asm-generic, switch the test over and then make it arm/m68k's
problem to define uaccess_user() to true?