mm/hmm: unregister mmu_notifier when last HMM client quit
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.
Link: http://lkml.kernel.org/r/20180323005527.758-5-jglisse@redhat.com
Signed-off-by: Jérôme Glisse <jglisse@redhat.com>
Cc: Evgeny Baskakov <ebaskakov@nvidia.com>
Cc: Ralph Campbell <rcampbell@nvidia.com>
Cc: Mark Hairgrove <mhairgrove@nvidia.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/hmm.c b/mm/hmm.c
index 8116727..2d00769 100644
--- a/mm/hmm.c
+++ b/mm/hmm.c
@@ -233,13 +233,24 @@ int hmm_mirror_register(struct hmm_mirror *mirror, struct mm_struct *mm)
if (!mm || !mirror || !mirror->ops)
return -EINVAL;
+again:
mirror->hmm = hmm_register(mm);
if (!mirror->hmm)
return -ENOMEM;
down_write(&mirror->hmm->mirrors_sem);
- list_add(&mirror->list, &mirror->hmm->mirrors);
- up_write(&mirror->hmm->mirrors_sem);
+ if (mirror->hmm->mm == NULL) {
+ /*
+ * A racing hmm_mirror_unregister() is about to destroy the hmm
+ * struct. Try again to allocate a new one.
+ */
+ up_write(&mirror->hmm->mirrors_sem);
+ mirror->hmm = NULL;
+ goto again;
+ } else {
+ list_add(&mirror->list, &mirror->hmm->mirrors);
+ up_write(&mirror->hmm->mirrors_sem);
+ }
return 0;
}
@@ -254,11 +265,32 @@ EXPORT_SYMBOL(hmm_mirror_register);
*/
void hmm_mirror_unregister(struct hmm_mirror *mirror)
{
- struct hmm *hmm = mirror->hmm;
+ bool should_unregister = false;
+ struct mm_struct *mm;
+ struct hmm *hmm;
+ if (mirror->hmm == NULL)
+ return;
+
+ hmm = mirror->hmm;
down_write(&hmm->mirrors_sem);
list_del_init(&mirror->list);
+ should_unregister = list_empty(&hmm->mirrors);
+ mirror->hmm = NULL;
+ mm = hmm->mm;
+ hmm->mm = NULL;
up_write(&hmm->mirrors_sem);
+
+ if (!should_unregister || mm == NULL)
+ return;
+
+ spin_lock(&mm->page_table_lock);
+ if (mm->hmm == hmm)
+ mm->hmm = NULL;
+ spin_unlock(&mm->page_table_lock);
+
+ mmu_notifier_unregister_no_release(&hmm->mmu_notifier, mm);
+ kfree(hmm);
}
EXPORT_SYMBOL(hmm_mirror_unregister);
