[PATCH v4 1/4] lazy tlb: introduce lazy mm refcount helper functions

[Andrew Morton]

On Tue, 08 Jun 2021 11:39:56 +1000 Nicholas Piggin <npiggin at gmail.com> wrote:

> > Looks like a functional change.  What's happening here?
> 
> That's kthread_use_mm being clever about the lazy tlb mm. If it happened 
> that the kthread had inherited a the lazy tlb mm that happens to be the 
> one we want to use here, then we already have a refcount to it via the 
> lazy tlb ref.
> 
> So then it doesn't have to touch the refcount, but rather just converts
> it from the lazy tlb ref to the returned reference. If the lazy tlb mm
> doesn't get a reference, we can't do that.

Please cover this in the changelog and perhaps a code comment.