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    SubjectRe: [PATCH 3/4] mmap locking API: Don't check locking if the mm isn't live yet
    On Fri, Oct 2, 2020 at 1:41 AM Jason Gunthorpe <jgg@ziepe.ca> wrote:
    > On Thu, Oct 01, 2020 at 10:16:35PM +0200, Jann Horn wrote:
    > > > A subclass isn't right, it has to be a _nested annotation.
    > > >
    > > > nested locking is a pretty good reason to not be able to do this, this
    > > > is something lockdep does struggle to model.
    > >
    > > Did I get the terminology wrong? I thought they were the same. The
    > > down_*_nested() APIs take an argument "subclass", with the default
    > > subclass for the functions without "_nested" being 0.
    >
    > AFAIK a subclass at init time sticks with the lock forever, the
    > _nested ones are temporary overrides.
    >
    > I think what you kind of want is to start out with
    > lockdep_set_novalidate_class() then switch to a real class once things
    > are finished. Not sure exactly how :)

    Huh, is there an API that sets a *subclass* (not a class) at init
    time? I don't think there is.

    Anyway, I'm pretty sure I just need to use the normal _nested()
    locking API. I'm still cleaning up and testing a little bit, but I'll
    send it out in a short while, unless I run into unexpected trouble.
    Let's continue this if necessary once there's a concrete patch to talk
    about. :)

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