From: Qian Cai <cai@lca.pw>
To: peterz@infradead.org, mingo@redhat.com
Cc: will@kernel.org, elver@google.com, linux-kernel@vger.kernel.org,
Qian Cai <cai@lca.pw>
Subject: [PATCH -next v2] locking/osq_lock: annotate a data race in osq_lock
Date: Tue, 11 Feb 2020 08:54:15 -0500 [thread overview]
Message-ID: <1581429255-12542-1-git-send-email-cai@lca.pw> (raw)
prev->next could be accessed concurrently as noticed by KCSAN,
write (marked) to 0xffff9d3370dbbe40 of 8 bytes by task 3294 on cpu 107:
osq_lock+0x25f/0x350
osq_wait_next at kernel/locking/osq_lock.c:79
(inlined by) osq_lock at kernel/locking/osq_lock.c:185
rwsem_optimistic_spin
<snip>
read to 0xffff9d3370dbbe40 of 8 bytes by task 3398 on cpu 100:
osq_lock+0x196/0x350
osq_lock at kernel/locking/osq_lock.c:157
rwsem_optimistic_spin
<snip>
Since the write only stores NULL to prev->next and the read tests if
prev->next equals to this_cpu_ptr(&osq_node). Even if the value is
shattered, the code is still working correctly. Thus, mark it as an
intentional data race using the data_race() macro.
Signed-off-by: Qian Cai <cai@lca.pw>
---
v2: insert some code comments.
kernel/locking/osq_lock.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/kernel/locking/osq_lock.c b/kernel/locking/osq_lock.c
index 1f7734949ac8..f733bcd99e8a 100644
--- a/kernel/locking/osq_lock.c
+++ b/kernel/locking/osq_lock.c
@@ -154,7 +154,11 @@ bool osq_lock(struct optimistic_spin_queue *lock)
*/
for (;;) {
- if (prev->next == node &&
+ /*
+ * cpu_relax() below implies a compiler barrier which would
+ * prevent this comparison being optimized away.
+ */
+ if (data_race(prev->next == node) &&
cmpxchg(&prev->next, node, NULL) == node)
break;
--
1.8.3.1
next reply other threads:[~2020-02-11 13:54 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-11 13:54 Qian Cai [this message]
2020-05-08 20:59 ` [PATCH -next v2] locking/osq_lock: annotate a data race in osq_lock Qian Cai
2020-05-09 4:33 ` Paul E. McKenney
2020-05-09 13:01 ` Qian Cai
2020-05-09 16:12 ` Paul E. McKenney
2020-05-09 16:53 ` Qian Cai
2020-05-09 21:36 ` Paul E. McKenney
2020-05-11 15:58 ` Will Deacon
2020-05-11 16:43 ` Paul E. McKenney
2020-05-11 16:52 ` Will Deacon
2020-05-11 17:29 ` Paul E. McKenney
2020-05-11 17:34 ` Will Deacon
2020-05-11 18:07 ` Paul E. McKenney
2020-05-11 16:44 ` Qian Cai
2020-05-11 16:54 ` Will Deacon
2020-05-11 17:10 ` Qian Cai
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