From: Qian Cai <cai@xxxxxx>
Subject: mm/vmscan.c: fix data races using kswapd_classzone_idx
pgdat->kswapd_classzone_idx could be accessed concurrently in
wakeup_kswapd(). Plain writes and reads without any lock protection
result in data races. Fix them by adding a pair of READ|WRITE_ONCE() as
well as saving a branch (compilers might well optimize the original code
in an unintentional way anyway). While at it, also take care of
pgdat->kswapd_order and non-kswapd threads in allow_direct_reclaim(). The
data races were reported by KCSAN,
BUG: KCSAN: data-race in wakeup_kswapd / wakeup_kswapd
write to 0xffff9f427ffff2dc of 4 bytes by task 7454 on cpu 13:
wakeup_kswapd+0xf1/0x400
wakeup_kswapd at mm/vmscan.c:3967
wake_all_kswapds+0x59/0xc0
wake_all_kswapds at mm/page_alloc.c:4241
__alloc_pages_slowpath+0xdcc/0x1290
__alloc_pages_slowpath at mm/page_alloc.c:4512
__alloc_pages_nodemask+0x3bb/0x450
alloc_pages_vma+0x8a/0x2c0
do_anonymous_page+0x16e/0x6f0
__handle_mm_fault+0xcd5/0xd40
handle_mm_fault+0xfc/0x2f0
do_page_fault+0x263/0x6f9
page_fault+0x34/0x40
1 lock held by mtest01/7454:
#0: ffff9f425afe8808 (&mm->mmap_sem#2){++++}, at:
do_page_fault+0x143/0x6f9
do_user_addr_fault at arch/x86/mm/fault.c:1405
(inlined by) do_page_fault at arch/x86/mm/fault.c:1539
irq event stamp: 6944085
count_memcg_event_mm+0x1a6/0x270
count_memcg_event_mm+0x119/0x270
__do_softirq+0x34c/0x57c
irq_exit+0xa2/0xc0
read to 0xffff9f427ffff2dc of 4 bytes by task 7472 on cpu 38:
wakeup_kswapd+0xc8/0x400
wake_all_kswapds+0x59/0xc0
__alloc_pages_slowpath+0xdcc/0x1290
__alloc_pages_nodemask+0x3bb/0x450
alloc_pages_vma+0x8a/0x2c0
do_anonymous_page+0x16e/0x6f0
__handle_mm_fault+0xcd5/0xd40
handle_mm_fault+0xfc/0x2f0
do_page_fault+0x263/0x6f9
page_fault+0x34/0x40
1 lock held by mtest01/7472:
#0: ffff9f425a9ac148 (&mm->mmap_sem#2){++++}, at:
do_page_fault+0x143/0x6f9
irq event stamp: 6793561
count_memcg_event_mm+0x1a6/0x270
count_memcg_event_mm+0x119/0x270
__do_softirq+0x34c/0x57c
irq_exit+0xa2/0xc0
BUG: KCSAN: data-race in kswapd / wakeup_kswapd
write to 0xffff90973ffff2dc of 4 bytes by task 820 on cpu 6:
kswapd+0x27c/0x8d0
kthread+0x1e0/0x200
ret_from_fork+0x27/0x50
read to 0xffff90973ffff2dc of 4 bytes by task 6299 on cpu 0:
wakeup_kswapd+0xf3/0x450
wake_all_kswapds+0x59/0xc0
__alloc_pages_slowpath+0xdcc/0x1290
__alloc_pages_nodemask+0x3bb/0x450
alloc_pages_vma+0x8a/0x2c0
do_anonymous_page+0x170/0x700
__handle_mm_fault+0xc9f/0xd00
handle_mm_fault+0xfc/0x2f0
do_page_fault+0x263/0x6f9
page_fault+0x34/0x40
Link: http://lkml.kernel.org/r/1582749472-5171-1-git-send-email-cai@xxxxxx
Signed-off-by: Qian Cai <cai@xxxxxx>
Reviewed-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Marco Elver <elver@xxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/vmscan.c | 45 ++++++++++++++++++++++++++-------------------
1 file changed, 26 insertions(+), 19 deletions(-)
--- a/mm/vmscan.c~mm-vmscan-fix-data-races-at-kswapd_classzone_idx
+++ a/mm/vmscan.c
@@ -3136,8 +3136,9 @@ static bool allow_direct_reclaim(pg_data
/* kswapd must be awake if processes are being throttled */
if (!wmark_ok && waitqueue_active(&pgdat->kswapd_wait)) {
- pgdat->kswapd_classzone_idx = min(pgdat->kswapd_classzone_idx,
- (enum zone_type)ZONE_NORMAL);
+ if (READ_ONCE(pgdat->kswapd_classzone_idx) > ZONE_NORMAL)
+ WRITE_ONCE(pgdat->kswapd_classzone_idx, ZONE_NORMAL);
+
wake_up_interruptible(&pgdat->kswapd_wait);
}
@@ -3769,9 +3770,9 @@ out:
static enum zone_type kswapd_classzone_idx(pg_data_t *pgdat,
enum zone_type prev_classzone_idx)
{
- if (pgdat->kswapd_classzone_idx == MAX_NR_ZONES)
- return prev_classzone_idx;
- return pgdat->kswapd_classzone_idx;
+ enum zone_type curr_idx = READ_ONCE(pgdat->kswapd_classzone_idx);
+
+ return curr_idx == MAX_NR_ZONES ? prev_classzone_idx : curr_idx;
}
static void kswapd_try_to_sleep(pg_data_t *pgdat, int alloc_order, int reclaim_order,
@@ -3815,8 +3816,11 @@ static void kswapd_try_to_sleep(pg_data_
* the previous request that slept prematurely.
*/
if (remaining) {
- pgdat->kswapd_classzone_idx = kswapd_classzone_idx(pgdat, classzone_idx);
- pgdat->kswapd_order = max(pgdat->kswapd_order, reclaim_order);
+ WRITE_ONCE(pgdat->kswapd_classzone_idx,
+ kswapd_classzone_idx(pgdat, classzone_idx));
+
+ if (READ_ONCE(pgdat->kswapd_order) < reclaim_order)
+ WRITE_ONCE(pgdat->kswapd_order, reclaim_order);
}
finish_wait(&pgdat->kswapd_wait, &wait);
@@ -3893,12 +3897,12 @@ static int kswapd(void *p)
tsk->flags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD;
set_freezable();
- pgdat->kswapd_order = 0;
- pgdat->kswapd_classzone_idx = MAX_NR_ZONES;
+ WRITE_ONCE(pgdat->kswapd_order, 0);
+ WRITE_ONCE(pgdat->kswapd_classzone_idx, MAX_NR_ZONES);
for ( ; ; ) {
bool ret;
- alloc_order = reclaim_order = pgdat->kswapd_order;
+ alloc_order = reclaim_order = READ_ONCE(pgdat->kswapd_order);
classzone_idx = kswapd_classzone_idx(pgdat, classzone_idx);
kswapd_try_sleep:
@@ -3906,10 +3910,10 @@ kswapd_try_sleep:
classzone_idx);
/* Read the new order and classzone_idx */
- alloc_order = reclaim_order = pgdat->kswapd_order;
+ alloc_order = reclaim_order = READ_ONCE(pgdat->kswapd_order);
classzone_idx = kswapd_classzone_idx(pgdat, classzone_idx);
- pgdat->kswapd_order = 0;
- pgdat->kswapd_classzone_idx = MAX_NR_ZONES;
+ WRITE_ONCE(pgdat->kswapd_order, 0);
+ WRITE_ONCE(pgdat->kswapd_classzone_idx, MAX_NR_ZONES);
ret = try_to_freeze();
if (kthread_should_stop())
@@ -3953,20 +3957,23 @@ void wakeup_kswapd(struct zone *zone, gf
enum zone_type classzone_idx)
{
pg_data_t *pgdat;
+ enum zone_type curr_idx;
if (!managed_zone(zone))
return;
if (!cpuset_zone_allowed(zone, gfp_flags))
return;
+
pgdat = zone->zone_pgdat;
+ curr_idx = READ_ONCE(pgdat->kswapd_classzone_idx);
+
+ if (curr_idx == MAX_NR_ZONES || curr_idx < classzone_idx)
+ WRITE_ONCE(pgdat->kswapd_classzone_idx, classzone_idx);
+
+ if (READ_ONCE(pgdat->kswapd_order) < order)
+ WRITE_ONCE(pgdat->kswapd_order, order);
- if (pgdat->kswapd_classzone_idx == MAX_NR_ZONES)
- pgdat->kswapd_classzone_idx = classzone_idx;
- else
- pgdat->kswapd_classzone_idx = max(pgdat->kswapd_classzone_idx,
- classzone_idx);
- pgdat->kswapd_order = max(pgdat->kswapd_order, order);
if (!waitqueue_active(&pgdat->kswapd_wait))
return;
_
