As all the other places, we grab the lock before manipulate the defer list. Current implementation may face a race condition.
For example, the potential race would be:
CPU1 CPU2 mem_cgroup_move_account deferred_split_huge_page list_empty lock list_empty list_add_tail unlock lock # list_empty might not hold anymore list_add_tail unlock
When this sequence happens, the list_add_tail() in mem_cgroup_move_account() corrupt the list since which is already been added to some split_queue in split_huge_page_to_list().
Besides this, David Rientjes points out the split_queue_len would be in a wrong state, which would be a significant issue for shrinkers.
Fixes: 87eaceb3faa5 ("mm: thp: make deferred split shrinker memcg aware")
Signed-off-by: Wei Yang richardw.yang@linux.intel.com Cc: stable@vger.kernel.org [5.4+]
--- v3: * remove all review/ack tag since rewrite the changelog * use deferred_split_huge_page as the example of race * add cc stable 5.4+ tag as suggested by David Rientjes
v2: * move check on compound outside suggested by Alexander * an example of the race condition, suggested by Michal --- mm/memcontrol.c | 18 +++++++++++------- 1 file changed, 11 insertions(+), 7 deletions(-)
diff --git a/mm/memcontrol.c b/mm/memcontrol.c index c5b5f74cfd4d..6450bbe394e2 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -5360,10 +5360,12 @@ static int mem_cgroup_move_account(struct page *page, }
#ifdef CONFIG_TRANSPARENT_HUGEPAGE - if (compound && !list_empty(page_deferred_list(page))) { + if (compound) { spin_lock(&from->deferred_split_queue.split_queue_lock); - list_del_init(page_deferred_list(page)); - from->deferred_split_queue.split_queue_len--; + if (!list_empty(page_deferred_list(page))) { + list_del_init(page_deferred_list(page)); + from->deferred_split_queue.split_queue_len--; + } spin_unlock(&from->deferred_split_queue.split_queue_lock); } #endif @@ -5377,11 +5379,13 @@ static int mem_cgroup_move_account(struct page *page, page->mem_cgroup = to;
#ifdef CONFIG_TRANSPARENT_HUGEPAGE - if (compound && list_empty(page_deferred_list(page))) { + if (compound) { spin_lock(&to->deferred_split_queue.split_queue_lock); - list_add_tail(page_deferred_list(page), - &to->deferred_split_queue.split_queue); - to->deferred_split_queue.split_queue_len++; + if (list_empty(page_deferred_list(page))) { + list_add_tail(page_deferred_list(page), + &to->deferred_split_queue.split_queue); + to->deferred_split_queue.split_queue_len++; + } spin_unlock(&to->deferred_split_queue.split_queue_lock); } #endif