From: Qian Cai <cai@lca.pw>
To: akpm@linux-foundation.org
Cc: elver@google.com, linux-mm@kvack.org,
linux-kernel@vger.kernel.org, Qian Cai <cai@lca.pw>
Subject: [PATCH] mm/vmscan: fix data races at kswapd_classzone_idx
Date: Tue, 25 Feb 2020 11:55:26 -0500 [thread overview]
Message-ID: <1582649726-15474-1-git-send-email-cai@lca.pw> (raw)
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). 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
Signed-off-by: Qian Cai <cai@lca.pw>
---
mm/vmscan.c | 9 ++++-----
1 file changed, 4 insertions(+), 5 deletions(-)
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 876370565455..400950734e5a 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -3961,11 +3961,10 @@ void wakeup_kswapd(struct zone *zone, gfp_t gfp_flags, int order,
return;
pgdat = zone->zone_pgdat;
- 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);
+ if (READ_ONCE(pgdat->kswapd_classzone_idx) == MAX_NR_ZONES ||
+ READ_ONCE(pgdat->kswapd_classzone_idx) < classzone_idx)
+ WRITE_ONCE(pgdat->kswapd_classzone_idx, classzone_idx);
+
pgdat->kswapd_order = max(pgdat->kswapd_order, order);
if (!waitqueue_active(&pgdat->kswapd_wait))
return;
--
1.8.3.1
next reply other threads:[~2020-02-25 16:55 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-25 16:55 Qian Cai [this message]
2020-02-26 1:29 ` [PATCH] mm/vmscan: fix data races at kswapd_classzone_idx Matthew Wilcox
2020-02-26 1:48 ` Qian Cai
2020-02-26 2:11 ` Andrew Morton
2020-02-26 2:26 ` Qian Cai
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