From: Qian Cai cai@lca.pw
mainline inclusion from mainline-v5.9-rc1 commit a1f459354a0f011a7baf52e5f16cd9ca95f1e6f2 category: bugfix bugzilla: 41543 CVE: NA
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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 cai@lca.pw Signed-off-by: Andrew Morton akpm@linux-foundation.org Cc: Marco Elver elver@google.com Cc: Konrad Rzeszutek Wilk konrad.wilk@oracle.com Link: http://lkml.kernel.org/r/1581114679-5488-1-git-send-email-cai@lca.pw Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Liu Shixin liushixin2@huawei.com Reviewed-by: Chen Wandun chenwandun@huawei.com Signed-off-by: Yang Yingliang yangyingliang@huawei.com --- 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 2961b87ccae72..24e76a91902fd 100644 --- a/mm/list_lru.c +++ b/mm/list_lru.c @@ -189,7 +189,7 @@ 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;