From: Qian Cai cai@lca.pw
[ Upstream commit 5644e1fbbfe15ad06785502bbfe5751223e5841d ]
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
Signed-off-by: Qian Cai cai@lca.pw Signed-off-by: Andrew Morton akpm@linux-foundation.org Reviewed-by: Andrew Morton akpm@linux-foundation.org Cc: Marco Elver elver@google.com Cc: Matthew Wilcox willy@infradead.org Link: http://lkml.kernel.org/r/1582749472-5171-1-git-send-email-cai@lca.pw Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Sasha Levin sashal@kernel.org --- mm/vmscan.c | 45 ++++++++++++++++++++++++++------------------- 1 file changed, 26 insertions(+), 19 deletions(-)
diff --git a/mm/vmscan.c b/mm/vmscan.c index 7fde5f904c8d3..d0404d8b37254 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -3160,8 +3160,9 @@ static bool allow_direct_reclaim(pg_data_t *pgdat)
/* 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); }
@@ -3793,9 +3794,9 @@ 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, @@ -3839,8 +3840,11 @@ static void kswapd_try_to_sleep(pg_data_t *pgdat, int alloc_order, int reclaim_o * 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); @@ -3917,12 +3921,12 @@ 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: @@ -3930,10 +3934,10 @@ 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()) @@ -3977,20 +3981,23 @@ void wakeup_kswapd(struct zone *zone, gfp_t gfp_flags, int order, 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;