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mm: memcg: use READ_ONCE()/WRITE_ONCE() to access stock->cached

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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 <roman.gushchin@linux.dev>
Acked-by: Shakeel Butt <shakeelb@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Yosry Ahmed <yosryahmed@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Roman Gushchin 2023-05-02 09:08:39 -07:00 committed by Andrew Morton
parent 3b8abb3239
commit f785a8f21a
1 changed files with 6 additions and 6 deletions
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12
mm/memcontrol.c
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@ -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;