Re: bad rss-counter message in 3.14rc5

From: Linus Torvalds
Date: Tue Mar 18 2014 - 21:10:51 EST

On Tue, Mar 18, 2014 at 5:38 PM, Hugh Dickins <hughd@xxxxxxxxxx> wrote:
> And yes, it is possible (though very unusual) to find an anon page or
> swap entry in a VM_SHARED nonlinear mapping: coming from that horrid
> get_user_pages(write, force) case which COWs even in a shared mapping.

Hmm. Maybe we could just disallow that forced case.

It *used* to be a trivial "we can just do a COW", but that was back
when the VM was much simpler and we had no rmap's etc. So "that horrid
case" used to be a simple hack that wasn't painful. But I suspect we
could very easily just fail it instead of forcing a COW, if that would
make it simpler for the VM code.

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