On Tue, 08 Jun 2021 11:39:56 +1000 Nicholas Piggin <npiggin@xxxxxxxxx> 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.
