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Subject[RFC PATCH] mm: thp: grab the lock before manipulation defer list
Date
As all the other places, we grab the lock before manipulate the defer list.
Current implementation may face a race condition.

Fixes: 87eaceb3faa5 ("mm: thp: make deferred split shrinker memcg aware")

Signed-off-by: Wei Yang <richardw.yang@linux.intel.com>

---
I notice the difference during code reading and just confused about the
difference. No specific test is done since limited knowledge about cgroup.

Maybe I miss something important?
---
mm/memcontrol.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index bc01423277c5..62b7ec34ef1a 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -5368,12 +5368,12 @@ static int mem_cgroup_move_account(struct page *page,
}

#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+ spin_lock(&from->deferred_split_queue.split_queue_lock);
if (compound && !list_empty(page_deferred_list(page))) {
- spin_lock(&from->deferred_split_queue.split_queue_lock);
list_del_init(page_deferred_list(page));
from->deferred_split_queue.split_queue_len--;
- spin_unlock(&from->deferred_split_queue.split_queue_lock);
}
+ spin_unlock(&from->deferred_split_queue.split_queue_lock);
#endif
/*
* It is safe to change page->mem_cgroup here because the page
@@ -5385,13 +5385,13 @@ static int mem_cgroup_move_account(struct page *page,
page->mem_cgroup = to;

#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+ spin_lock(&to->deferred_split_queue.split_queue_lock);
if (compound && list_empty(page_deferred_list(page))) {
- 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++;
- spin_unlock(&to->deferred_split_queue.split_queue_lock);
}
+ spin_unlock(&to->deferred_split_queue.split_queue_lock);
#endif

spin_unlock_irqrestore(&from->move_lock, flags);
--
2.17.1
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