Re: [patch 12/21] Xen-paravirt: Allocate and free vmalloc areas

Andrew Morton
2007-02-16T07:25:57Z

On Thu, 15 Feb 2007 23:08:02 -0800 Jeremy Fitzhardinge <jeremy@goop.org> wrote:

> Andrew Morton wrote:
> > This won't work when CONFIG_PREEMPT=y. The pagefault handler will see
> > in_atomic() and will scram.
> >
>
> Is there some other way to get the pagetable populated for the address
> range?
>

If you really need to run atomically, that gets ugly. Even of one were to
run handle_mm_fault() by hand, it still needs to allocate memory.

Two ugly options might be:

a) touch all the pages, then go atomic, then touch them all again. If
one of them faults (ie: you raced with swapout) then go back and try
again. Obviously susceptible to livelocking.

b) Do get_user_pages() against all the pages, then go atomic, then do
put_page() against them all. Of course, they can immediately get
swapped out.

But that function's already racy against swapout and I guess it works OK.
I don't have clue what it is actually trying to do, so I'm guessing madly
here.