From f785a8f21a9cc46fced9f53c51a6f2dc647ed484 Mon Sep 17 00:00:00 2001 From: Roman Gushchin Date: Tue, 2 May 2023 09:08:39 -0700 Subject: [PATCH] mm: memcg: use READ_ONCE()/WRITE_ONCE() to access stock->cached A memcg pointer in the percpu stock can be accessed by drain_all_stock() from another cpu in a lockless way. In theory it might lead to an issue, similar to the one which has been discovered with stock->cached_objcg, where the pointer was zeroed between the check for being NULL and dereferencing. In this case the issue is unlikely a real problem, but to make it bulletproof and similar to stock->cached_objcg, let's annotate all accesses to stock->cached with READ_ONCE()/WTRITE_ONCE(). Link: https://lkml.kernel.org/r/20230502160839.361544-2-roman.gushchin@linux.dev Signed-off-by: Roman Gushchin Acked-by: Shakeel Butt Cc: Dmitry Vyukov Cc: Yosry Ahmed Signed-off-by: Andrew Morton --- mm/memcontrol.c | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index c823c35c2ed4..1e364ad495a3 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -2275,7 +2275,7 @@ static bool consume_stock(struct mem_cgroup *memcg, unsigned int nr_pages) local_lock_irqsave(&memcg_stock.stock_lock, flags); stock = this_cpu_ptr(&memcg_stock); - if (memcg == stock->cached && stock->nr_pages >= nr_pages) { + if (memcg == READ_ONCE(stock->cached) && stock->nr_pages >= nr_pages) { stock->nr_pages -= nr_pages; ret = true; } @@ -2290,7 +2290,7 @@ static bool consume_stock(struct mem_cgroup *memcg, unsigned int nr_pages) */ static void drain_stock(struct memcg_stock_pcp *stock) { - struct mem_cgroup *old = stock->cached; + struct mem_cgroup *old = READ_ONCE(stock->cached); if (!old) return; @@ -2303,7 +2303,7 @@ static void drain_stock(struct memcg_stock_pcp *stock) } css_put(&old->css); - stock->cached = NULL; + WRITE_ONCE(stock->cached, NULL); } static void drain_local_stock(struct work_struct *dummy) @@ -2338,10 +2338,10 @@ static void __refill_stock(struct mem_cgroup *memcg, unsigned int nr_pages) struct memcg_stock_pcp *stock; stock = this_cpu_ptr(&memcg_stock); - if (stock->cached != memcg) { /* reset if necessary */ + if (READ_ONCE(stock->cached) != memcg) { /* reset if necessary */ drain_stock(stock); css_get(&memcg->css); - stock->cached = memcg; + WRITE_ONCE(stock->cached, memcg); } stock->nr_pages += nr_pages; @@ -2383,7 +2383,7 @@ static void drain_all_stock(struct mem_cgroup *root_memcg) bool flush = false; rcu_read_lock(); - memcg = stock->cached; + memcg = READ_ONCE(stock->cached); if (memcg && stock->nr_pages && mem_cgroup_is_descendant(memcg, root_memcg)) flush = true; -- 2.11.0