mm/hmm: fix race between hmm_mirror_unregister() and mmu_notifier callback
In hmm_mirror_unregister(), mm->hmm is set to NULL and then
mmu_notifier_unregister_no_release() is called. That creates a small
window where mmu_notifier can call mmu_notifier_ops with mm->hmm equal to
NULL. Fix this by first unregistering mmu notifier callbacks and then
setting mm->hmm to NULL.
Similarly in hmm_register(), set mm->hmm before registering mmu_notifier
callbacks so callback functions always see mm->hmm set.
Link: http://lkml.kernel.org/r/20181019160442.18723-4-jglisse@redhat.com
Signed-off-by: Ralph Campbell <rcampbell@nvidia.com>
Signed-off-by: Jérôme Glisse <jglisse@redhat.com>
Reviewed-by: John Hubbard <jhubbard@nvidia.com>
Reviewed-by: Jérôme Glisse <jglisse@redhat.com>
Reviewed-by: Balbir Singh <bsingharora@gmail.com>
Cc: <stable@vger.kernel.org>
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 de9840f..63ca3b5 100644
--- a/mm/hmm.c
+++ b/mm/hmm.c
@@ -91,16 +91,6 @@ static struct hmm *hmm_register(struct mm_struct *mm)
spin_lock_init(&hmm->lock);
hmm->mm = mm;
- /*
- * We should only get here if hold the mmap_sem in write mode ie on
- * registration of first mirror through hmm_mirror_register()
- */
- hmm->mmu_notifier.ops = &hmm_mmu_notifier_ops;
- if (__mmu_notifier_register(&hmm->mmu_notifier, mm)) {
- kfree(hmm);
- return NULL;
- }
-
spin_lock(&mm->page_table_lock);
if (!mm->hmm)
mm->hmm = hmm;
@@ -108,12 +98,27 @@ static struct hmm *hmm_register(struct mm_struct *mm)
cleanup = true;
spin_unlock(&mm->page_table_lock);
- if (cleanup) {
- mmu_notifier_unregister(&hmm->mmu_notifier, mm);
- kfree(hmm);
- }
+ if (cleanup)
+ goto error;
+
+ /*
+ * We should only get here if hold the mmap_sem in write mode ie on
+ * registration of first mirror through hmm_mirror_register()
+ */
+ hmm->mmu_notifier.ops = &hmm_mmu_notifier_ops;
+ if (__mmu_notifier_register(&hmm->mmu_notifier, mm))
+ goto error_mm;
return mm->hmm;
+
+error_mm:
+ spin_lock(&mm->page_table_lock);
+ if (mm->hmm == hmm)
+ mm->hmm = NULL;
+ spin_unlock(&mm->page_table_lock);
+error:
+ kfree(hmm);
+ return NULL;
}
void hmm_mm_destroy(struct mm_struct *mm)
@@ -278,12 +283,13 @@ void hmm_mirror_unregister(struct hmm_mirror *mirror)
if (!should_unregister || mm == NULL)
return;
+ mmu_notifier_unregister_no_release(&hmm->mmu_notifier, mm);
+
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);
