On Fri, Jan 08, 2021 at 11:08:58PM +0000, Luck, Tony wrote:

quoted

I think this is horrid; why can't we have it return something different
then -EFAULT instead?

I did consider this ... but it appears that architectures aren't unified in the
return value from get_user()

But surely none are currently returning -EMEMERR or whatever name we
come up with.

Here's another function involved in the futex call chain leading to this:

static int get_futex_value_locked(u32 *dest, u32 __user *from)
{
        int ret;

        pagefault_disable();
        ret = __get_user(*dest, from);
        pagefault_enable();

        return ret ? -EFAULT : 0;
}

It seems like the expectation here is just "zero or not" and we
don't care what the "not" value is ... just turn it into -EFAULT.

Yeah, saw that, but that should be trivially fixable I'm thinking.