atomic copy_from_user?

[Albert Cahalan <albert@users.sf.net>]

Surely I'm not the only one wanting such a beast...?

>From some naughty place in the code where might_sleep
would trigger, I'd like to read from user memory.
I'll pretty much assume that mlockall() has been
called. Suppose that "current" is correct as well.
I'd just use a pointer directly, except that:

a. it isn't OK for the 4g/4g feature, s390, or sparc64
b. it causes the "sparse" type checker to complain
c. it will oops or worse if the user screwed up

If the page is swapped out, I want a failed copy.