Re: A question about PROT_NONE on ARM and ARM26

Scott Wood
2004-07-02T14:36:31Z

On Fri, Jul 02, 2004 at 12:53:54AM +0100, Jamie Lokier wrote:
> The ARM uaccess code was written before CONFIG_PREEMPT was added, and
> this couldn't happen then. It could panic a kernel now. I wonder why
> it hasn't been noticed. Maybe nobody turns on CONFIG_PREEMPT on ARM?

Given that such behavior implies some raciness in userspace, you'd
probably need either malicious or buggy user code to trigger it, and
in the latter case, you're limited to apps using threads. Thus, it's
probably not that surprising that it hasn't been seen.

It could also happen in other rare cases, such as if the page gets
swapped out, and you get an I/O error swapping it back in, or if
forced filesystem unmounting were implemented.

-Scott