The patch titled
Subject: mm: memcg: use READ_ONCE()/WRITE_ONCE() to access stock->nr_pages
has been added to the -mm mm-unstable branch. Its filename is
mm-memcg-use-read_once-write_once-to-access-stock-nr_pages.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-memcg-use-read_once-write_once-to-access-stock-nr_pages.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Breno Leitao <leitao@xxxxxxxxxx>
Subject: mm: memcg: use READ_ONCE()/WRITE_ONCE() to access stock->nr_pages
Date: Wed, 1 May 2024 02:54:20 -0700
A memcg pointer in the per-cpu stock can be accessed by drain_all_stock()
and consume_stock() in parallel, causing a potential race.
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@xxxxxxxxxx
Signed-off-by: Breno Leitao <leitao@xxxxxxxxxx>
Acked-by: Shakeel Butt <shakeel.butt@xxxxxxxxx>
Reviewed-by: Roman Gushchin <roman.gushchin@xxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Muchun Song <songmuchun@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/memcontrol.c | 24 +++++++++++++++---------
1 file changed, 15 insertions(+), 9 deletions(-)
--- a/mm/memcontrol.c~mm-memcg-use-read_once-write_once-to-access-stock-nr_pages
+++ a/mm/memcontrol.c
@@ -2468,6 +2468,7 @@ static void memcg_account_kmem(struct me
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_cgr
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_cgr
*/
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 wor
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_cg
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_c
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))
_
Patches currently in -mm which might be from leitao@xxxxxxxxxx are
memcg-fix-data-race-kcsan-bug-in-rstats.patch
mm-memcg-use-read_once-write_once-to-access-stock-nr_pages.patch
