The patch titled
Subject: mm: ksm: do not block on page lock when searching stable tree fix
has been removed from the -mm tree. Its filename was
mm-ksm-do-not-block-on-page-lock-when-searching-stable-tree-fix.patch
This patch was dropped because it was folded into mm-ksm-do-not-block-on-page-lock-when-searching-stable-tree.patch
------------------------------------------------------
From: Hugh Dickins <hughd@xxxxxxxxxx>
Subject: mm: ksm: do not block on page lock when searching stable tree fix
I hit the kernel BUG at mm/ksm.c:809! quite easily under KSM swapping
load. That's the BUG_ON(age > 1) in remove_rmap_item_from_tree().
There is a comment above it, but explaining in more detail: KSM saves
effort by not fully maintaining the unstable tree like a proper RB
tree throughout, but at the start of each pass forgetting the old tree
and rebuilding anew from scratch. But that means that whenever it looks
like we need to remove an item from the unstable tree, we have to check
whether it has already been linked into the new tree this time around
(hence rb_erase needed), or it's just a free-floating leftover from the
previous tree.
"age" 0 or 1 says which: but if it's more than 1, then something has
gone wrong: cmp_and_merge_page() was forgetting to remove the item
in the new EBUSY case.
Link: http://lkml.kernel.org/r/alpine.LSU.2.11.1902182122280.6914@eggly.anvils
Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Yang Shi <yang.shi@xxxxxxxxxxxxxxxxx>
Cc: John Hubbard <jhubbard@xxxxxxxxxx>
Cc: Kirill Tkhai <ktkhai@xxxxxxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/ksm.c | 7 +++----
1 file changed, 3 insertions(+), 4 deletions(-)
--- a/mm/ksm.c~mm-ksm-do-not-block-on-page-lock-when-searching-stable-tree-fix
+++ a/mm/ksm.c
@@ -2082,10 +2082,6 @@ static void cmp_and_merge_page(struct pa
/* We first start with searching the page inside the stable tree */
kpage = stable_tree_search(page);
-
- if (PTR_ERR(kpage) == -EBUSY)
- return;
-
if (kpage == page && rmap_item->head == stable_node) {
put_page(kpage);
return;
@@ -2094,6 +2090,9 @@ static void cmp_and_merge_page(struct pa
remove_rmap_item_from_tree(rmap_item);
if (kpage) {
+ if (PTR_ERR(kpage) == -EBUSY)
+ return;
+
err = try_to_merge_with_ksm_page(rmap_item, page, kpage);
if (!err) {
/*
_
Patches currently in -mm which might be from hughd@xxxxxxxxxx are
mm-ksm-do-not-block-on-page-lock-when-searching-stable-tree.patch
