[PATCH 04/15] mm/hmm: unregister mmu_notifier when last HMM client quit

[jglisse]

From: Jérôme Glisse <jgli...@redhat.com>

This code was lost in translation at one point. This properly call
mmu_notifier_unregister_no_release() once last user is gone. This
fix the zombie mm_struct as without this patch we do not drop the
refcount we have on it.

Signed-off-by: Jérôme Glisse <jgli...@redhat.com>
Cc: Evgeny Baskakov <ebaska...@nvidia.com>
Cc: Ralph Campbell <rcampb...@nvidia.com>
Cc: Mark Hairgrove <mhairgr...@nvidia.com>
Cc: John Hubbard <jhubb...@nvidia.com>
---
 mm/hmm.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/mm/hmm.c b/mm/hmm.c
index 6088fa6ed137..667944630dc9 100644
--- a/mm/hmm.c
+++ b/mm/hmm.c
@@ -244,10 +244,29 @@ EXPORT_SYMBOL(hmm_mirror_register);
 void hmm_mirror_unregister(struct hmm_mirror *mirror)
 {
        struct hmm *hmm = mirror->hmm;
+       struct mm_struct *mm = NULL;
+       bool unregister = false;
 
        down_write(&hmm->mirrors_sem);
        list_del_init(&mirror->list);
+       unregister = list_empty(&hmm->mirrors);
        up_write(&hmm->mirrors_sem);
+
+       if (!unregister)
+               return;
+
+       spin_lock(&hmm->mm->page_table_lock);
+       if (hmm->mm->hmm == hmm) {
+               mm = hmm->mm;
+               mm->hmm = NULL;
+       }
+       spin_unlock(&hmm->mm->page_table_lock);
+
+       if (mm == NULL)
+               return;
+
+       mmu_notifier_unregister_no_release(&hmm->mmu_notifier, mm);
+       kfree(hmm);
 }
 EXPORT_SYMBOL(hmm_mirror_unregister);
 
-- 
2.14.3