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authorBreno Leitao <leitao@debian.org>2024-05-01 12:54:20 +0300
committerAndrew Morton <akpm@linux-foundation.org>2024-05-07 20:37:00 +0300
commit1872b3bcd5874b57ed8c89cae0a2882f484c3885 (patch)
treee59a517350d21e6e4614ad2e2a9b0519d7a6cf78 /mm
parent3a5a8d343e1cf96eb9971b17cbd4b832ab19b8e7 (diff)
downloadlinux-1872b3bcd5874b57ed8c89cae0a2882f484c3885.tar.xz
mm: memcg: use READ_ONCE()/WRITE_ONCE() to access stock->nr_pages
A memcg pointer in the per-cpu stock can be accessed by drain_all_stock() and consume_stock() in parallel, causing a potential race, which is believed to e harmless. KCSAN shows this data-race clearly in the splat below: BUG: KCSAN: data-race in drain_all_stock.part.0 / try_charge_memcg write to 0xffff88903f8b0788 of 4 bytes by task 35901 on cpu 2: try_charge_memcg (mm/memcontrol.c:2323 mm/memcontrol.c:2746) __mem_cgroup_charge (mm/memcontrol.c:7287 mm/memcontrol.c:7301) do_anonymous_page (mm/memory.c:1054 mm/memory.c:4375 mm/memory.c:4433) __handle_mm_fault (mm/memory.c:3878 mm/memory.c:5300 mm/memory.c:5441) handle_mm_fault (mm/memory.c:5606) do_user_addr_fault (arch/x86/mm/fault.c:1363) exc_page_fault (./arch/x86/include/asm/irqflags.h:37 ./arch/x86/include/asm/irqflags.h:72 arch/x86/mm/fault.c:1513 arch/x86/mm/fault.c:1563) asm_exc_page_fault (./arch/x86/include/asm/idtentry.h:623) read to 0xffff88903f8b0788 of 4 bytes by task 287 on cpu 27: drain_all_stock.part.0 (mm/memcontrol.c:2433) mem_cgroup_css_offline (mm/memcontrol.c:5398 mm/memcontrol.c:5687) css_killed_work_fn (kernel/cgroup/cgroup.c:5521 kernel/cgroup/cgroup.c:5794) process_one_work (kernel/workqueue.c:3254) worker_thread (kernel/workqueue.c:3329 kernel/workqueue.c:3416) kthread (kernel/kthread.c:388) ret_from_fork (arch/x86/kernel/process.c:147) ret_from_fork_asm (arch/x86/entry/entry_64.S:257) value changed: 0x00000014 -> 0x00000013 This happens because drain_all_stock() is reading stock->nr_pages, while consume_stock() might be updating the same address, causing a potential data-race. Make the shared addresses bulletproof regarding to reads and writes, similarly to what stock->cached_objcg and stock->cached. Annotate all accesses to stock->nr_pages with READ_ONCE()/WRITE_ONCE(). Link: https://lkml.kernel.org/r/20240501095420.679208-1-leitao@debian.org Signed-off-by: Breno Leitao <leitao@debian.org> Acked-by: Shakeel Butt <shakeel.butt@linux.dev> Reviewed-by: Roman Gushchin <roman.gushchin@linux.dev> Acked-by: Michal Hocko <mhocko@suse.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Muchun Song <songmuchun@bytedance.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Diffstat (limited to 'mm')
-rw-r--r--mm/memcontrol.c24
1 files changed, 15 insertions, 9 deletions
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index e6302f42e40f..2103ae77cf8d 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2468,6 +2468,7 @@ static void memcg_account_kmem(struct mem_cgroup *memcg, int nr_pages)
static bool consume_stock(struct mem_cgroup *memcg, unsigned int nr_pages)
{
struct memcg_stock_pcp *stock;
+ unsigned int stock_pages;
unsigned long flags;
bool ret = false;
@@ -2477,8 +2478,9 @@ 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 == READ_ONCE(stock->cached) && stock->nr_pages >= nr_pages) {
- stock->nr_pages -= nr_pages;
+ stock_pages = READ_ONCE(stock->nr_pages);
+ if (memcg == READ_ONCE(stock->cached) && stock_pages >= nr_pages) {
+ WRITE_ONCE(stock->nr_pages, stock_pages - nr_pages);
ret = true;
}
@@ -2492,16 +2494,18 @@ static bool consume_stock(struct mem_cgroup *memcg, unsigned int nr_pages)
*/
static void drain_stock(struct memcg_stock_pcp *stock)
{
+ unsigned int stock_pages = READ_ONCE(stock->nr_pages);
struct mem_cgroup *old = READ_ONCE(stock->cached);
if (!old)
return;
- if (stock->nr_pages) {
- page_counter_uncharge(&old->memory, stock->nr_pages);
+ if (stock_pages) {
+ page_counter_uncharge(&old->memory, stock_pages);
if (do_memsw_account())
- page_counter_uncharge(&old->memsw, stock->nr_pages);
- stock->nr_pages = 0;
+ page_counter_uncharge(&old->memsw, stock_pages);
+
+ WRITE_ONCE(stock->nr_pages, 0);
}
css_put(&old->css);
@@ -2537,6 +2541,7 @@ static void drain_local_stock(struct work_struct *dummy)
static void __refill_stock(struct mem_cgroup *memcg, unsigned int nr_pages)
{
struct memcg_stock_pcp *stock;
+ unsigned int stock_pages;
stock = this_cpu_ptr(&memcg_stock);
if (READ_ONCE(stock->cached) != memcg) { /* reset if necessary */
@@ -2544,9 +2549,10 @@ static void __refill_stock(struct mem_cgroup *memcg, unsigned int nr_pages)
css_get(&memcg->css);
WRITE_ONCE(stock->cached, memcg);
}
- stock->nr_pages += nr_pages;
+ stock_pages = READ_ONCE(stock->nr_pages) + nr_pages;
+ WRITE_ONCE(stock->nr_pages, stock_pages);
- if (stock->nr_pages > MEMCG_CHARGE_BATCH)
+ if (stock_pages > MEMCG_CHARGE_BATCH)
drain_stock(stock);
}
@@ -2585,7 +2591,7 @@ static void drain_all_stock(struct mem_cgroup *root_memcg)
rcu_read_lock();
memcg = READ_ONCE(stock->cached);
- if (memcg && stock->nr_pages &&
+ if (memcg && READ_ONCE(stock->nr_pages) &&
mem_cgroup_is_descendant(memcg, root_memcg))
flush = true;
else if (obj_stock_flush_required(stock, root_memcg))