mm, rmap: Add yet more comments to page_get_anon_vma/page_lock_anon_vma
Inspired by an analysis from Hugh on why again all this doesn't explode
in our face.
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/rmap.c b/mm/rmap.c
index 6bada99..0eb463e 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -352,6 +352,11 @@
* The page might have been remapped to a different anon_vma or the anon_vma
* returned may already be freed (and even reused).
*
+ * In case it was remapped to a different anon_vma, the new anon_vma will be a
+ * child of the old anon_vma, and the anon_vma lifetime rules will therefore
+ * ensure that any anon_vma obtained from the page will still be valid for as
+ * long as we observe page_mapped() [ hence all those page_mapped() tests ].
+ *
* All users of this function must be very careful when walking the anon_vma
* chain and verify that the page in question is indeed mapped in it
* [ something equivalent to page_mapped_in_vma() ].
@@ -421,7 +426,7 @@
/*
* If the page is still mapped, then this anon_vma is still
* its anon_vma, and holding the mutex ensures that it will
- * not go away, see __put_anon_vma().
+ * not go away, see anon_vma_free().
*/
if (!page_mapped(page)) {
mutex_unlock(&root_anon_vma->mutex);