mm/hmm: Hold a mmgrab from hmm to mm

So long as a struct hmm pointer exists, so should the struct mm it is
linked too. Hold the mmgrab() as soon as a hmm is created, and mmdrop() it
once the hmm refcount goes to zero.

Since mmdrop() (ie a 0 kref on struct mm) is now impossible with a !NULL
mm->hmm delete the hmm_hmm_destroy().

Signed-off-by: Jason Gunthorpe <[email protected]>
Reviewed-by: Jérôme Glisse <[email protected]>
Reviewed-by: John Hubbard <[email protected]>
Reviewed-by: Ralph Campbell <[email protected]>
Reviewed-by: Ira Weiny <[email protected]>
Reviewed-by: Christoph Hellwig <[email protected]>
Tested-by: Philip Yang <[email protected]>

0 files changed, 0 insertions, 0 deletions