From: Jérôme Glisse <[email protected]>
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.
Changed since v1:
- close race window between a last mirror unregistering and a new
mirror registering, which could have lead to use after free()
kind of bug
Signed-off-by: Jérôme Glisse <[email protected]>
Cc: Evgeny Baskakov <[email protected]>
Cc: Ralph Campbell <[email protected]>
Cc: Mark Hairgrove <[email protected]>
Cc: John Hubbard <[email protected]>
---
mm/hmm.c | 35 +++++++++++++++++++++++++++++++++--
1 file changed, 33 insertions(+), 2 deletions(-)
diff --git a/mm/hmm.c b/mm/hmm.c
index 6088fa6ed137..f75aa8df6e97 100644
--- a/mm/hmm.c
+++ b/mm/hmm.c
@@ -222,13 +222,24 @@ 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;
}
@@ -244,10 +255,30 @@ 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;
+
+ if (list_empty(&mirror->list))
+ return;
down_write(&hmm->mirrors_sem);
list_del_init(&mirror->list);
+ should_unregister = list_empty(&hmm->mirrors);
+ 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);
--
2.14.3
