struct list_lru_one l.nr_items could be accessed concurrently as noticed
by KCSAN,
BUG: KCSAN: data-race in list_lru_count_one / list_lru_isolate_move
write to 0xffffa102789c4510 of 8 bytes by task 823 on cpu 39:
list_lru_isolate_move+0xf9/0x130
list_lru_isolate_move at mm/list_lru.c:180
inode_lru_isolate+0x12b/0x2a0
__list_lru_walk_one+0x122/0x3d0
list_lru_walk_one+0x75/0xa0
prune_icache_sb+0x8b/0xc0
super_cache_scan+0x1b8/0x250
do_shrink_slab+0x256/0x6d0
shrink_slab+0x41b/0x4a0
shrink_node+0x35c/0xd80
balance_pgdat+0x652/0xd90
kswapd+0x396/0x8d0
kthread+0x1e0/0x200
ret_from_fork+0x27/0x50
read to 0xffffa102789c4510 of 8 bytes by task 6345 on cpu 56:
list_lru_count_one+0x116/0x2f0
list_lru_count_one at mm/list_lru.c:193
super_cache_count+0xe8/0x170
do_shrink_slab+0x95/0x6d0
shrink_slab+0x41b/0x4a0
shrink_node+0x35c/0xd80
do_try_to_free_pages+0x1f7/0xa10
try_to_free_pages+0x26c/0x5e0
__alloc_pages_slowpath+0x458/0x1290
__alloc_pages_nodemask+0x3bb/0x450
alloc_pages_vma+0x8a/0x2c0
do_anonymous_page+0x170/0x700
__handle_mm_fault+0xc9f/0xd00
handle_mm_fault+0xfc/0x2f0
do_page_fault+0x263/0x6f9
page_fault+0x34/0x40
Reported by Kernel Concurrency Sanitizer on:
CPU: 56 PID: 6345 Comm: oom01 Tainted: G W L 5.5.0-next-20200205+ #4
Hardware name: HPE ProLiant DL385 Gen10/ProLiant DL385 Gen10, BIOS A40 07/10/2019
A shattered l.nr_items could affect the shrinker behaviour due to a data
race. Fix it by adding READ_ONCE() for the read. Since the writes are
aligned and up to word-size, assume those are safe from data races to
avoid readability issues of writing WRITE_ONCE(var, var + val).
Signed-off-by: Qian Cai <[email protected]>
---
mm/list_lru.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/mm/list_lru.c b/mm/list_lru.c
index 0f1f6b06b7f3..249468d06b9c 100644
--- a/mm/list_lru.c
+++ b/mm/list_lru.c
@@ -190,7 +190,7 @@ unsigned long list_lru_count_one(struct list_lru *lru,
rcu_read_lock();
l = list_lru_from_memcg_idx(nlru, memcg_cache_id(memcg));
- count = l->nr_items;
+ count = READ_ONCE(l->nr_items);
rcu_read_unlock();
return count;
--
1.8.3.1