The commit 3e32cb2e0a12 ("mm: memcontrol: lockless page counters") could
had memcg->memsw->watermark been accessed concurrently as reported by
KCSAN,
Reported by Kernel Concurrency Sanitizer on:
BUG: KCSAN: data-race in page_counter_try_charge / page_counter_try_charge
read to 0xffff8fb18c4cd190 of 8 bytes by task 1081 on cpu 59:
page_counter_try_charge+0x4d/0x150 mm/page_counter.c:138
try_charge+0x131/0xd50 mm/memcontrol.c:2405
__memcg_kmem_charge_memcg+0x58/0x140
__memcg_kmem_charge+0xcc/0x280
__alloc_pages_nodemask+0x1e1/0x450
alloc_pages_current+0xa6/0x120
pte_alloc_one+0x17/0xd0
__pte_alloc+0x3a/0x1f0
copy_p4d_range+0xc36/0x1990
copy_page_range+0x21d/0x360
dup_mmap+0x5f5/0x7a0
dup_mm+0xa2/0x240
copy_process+0x1b3f/0x3460
_do_fork+0xaa/0xa20
__x64_sys_clone+0x13b/0x170
do_syscall_64+0x91/0xb47
entry_SYSCALL_64_after_hwframe+0x49/0xbe
write to 0xffff8fb18c4cd190 of 8 bytes by task 1153 on cpu 120:
page_counter_try_charge+0x5b/0x150 mm/page_counter.c:139
try_charge+0x131/0xd50 mm/memcontrol.c:2405
mem_cgroup_try_charge+0x159/0x460
mem_cgroup_try_charge_delay+0x3d/0xa0
wp_page_copy+0x14d/0x930
do_wp_page+0x107/0x7b0
__handle_mm_fault+0xce6/0xd40
handle_mm_fault+0xfc/0x2f0
do_page_fault+0x263/0x6f9
page_fault+0x34/0x40
Since watermark could be compared or set to garbage due to load or
store tearing which would change the code logic, fix it by adding a pair
of READ_ONCE() and WRITE_ONCE() in those places.
Fixes: 3e32cb2e0a12 ("mm: memcontrol: lockless page counters")
Signed-off-by: Qian Cai <cai@xxxxxx>
---
mm/page_counter.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)
diff --git a/mm/page_counter.c b/mm/page_counter.c
index de31470655f6..a17841150906 100644
--- a/mm/page_counter.c
+++ b/mm/page_counter.c
@@ -82,8 +82,8 @@ void page_counter_charge(struct page_counter *counter, unsigned long nr_pages)
* This is indeed racy, but we can live with some
* inaccuracy in the watermark.
*/
- if (new > c->watermark)
- c->watermark = new;
+ if (new > READ_ONCE(c->watermark))
+ WRITE_ONCE(c->watermark, new);
}
}
@@ -135,8 +135,8 @@ bool page_counter_try_charge(struct page_counter *counter,
* Just like with failcnt, we can live with some
* inaccuracy in the watermark.
*/
- if (new > c->watermark)
- c->watermark = new;
+ if (new > READ_ONCE(c->watermark))
+ WRITE_ONCE(c->watermark, new);
}
return true;
--
2.21.0 (Apple Git-122.2)
