Re: [PATCH v2 2/3] lockdep: Remove BROKEN flag of LOCKDEP_CROSSRELEASE

[Thomas Gleixner]

On Thu, 19 Oct 2017, Bart Van Assche wrote:
> On Thu, 2017-10-19 at 13:33 -0700, Matthew Wilcox wrote:
> > For example, the page lock is not annotatable with lockdep -- we return
> > to userspace with it held, for heaven's sake!  So it is quite easy for
> > someone not familiar with the MM locking hierarchy to inadvertently
> > introduce an ABBA deadlock against the page lock.  (ie me.  I did that.)
> > Right now, that has to be caught by a human reviewer; if cross-release
> > checking can catch that, then it's worth having.
> 
> Hello Matthew,
> 
> Although I agree that enabling lock inversion checking for page locks is
> useful, I think my questions still apply to other locking objects than page
> locks.

Why are other objects any different?

    lock(L)   ->      wait_for_completion(A)
    lock(L)   ->      complete(A)

is a simple ABBA and they exist and have not been caught for a long time
until they choked a production machine.

Thanks,

	tglx