Messages in this thread Patch in this message | | | From | Qian Cai <> | Subject | [PATCH] locking/osq_lock: fix a data race in osq_wait_next | Date | Wed, 22 Jan 2020 11:38:57 -0500 |
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KCSAN complains,
write (marked) to 0xffff941ca3b3be00 of 8 bytes by task 670 on cpu 6: osq_lock+0x24c/0x340 __mutex_lock+0x277/0xd20 mutex_lock_nested+0x31/0x40 memcg_create_kmem_cache+0x2e/0x190 memcg_kmem_cache_create_func+0x40/0x80 process_one_work+0x54c/0xbe0 worker_thread+0x80/0x650 kthread+0x1e0/0x200 ret_from_fork+0x27/0x50
read to 0xffff941ca3b3be00 of 8 bytes by task 703 on cpu 44: osq_lock+0x18e/0x340 __mutex_lock+0x277/0xd20 mutex_lock_nested+0x31/0x40 memcg_create_kmem_cache+0x2e/0x190 memcg_kmem_cache_create_func+0x40/0x80 process_one_work+0x54c/0xbe0 worker_thread+0x80/0x650 kthread+0x1e0/0x200 ret_from_fork+0x27/0x50
which points to those lines in osq_wait_next(),
next = xchg(&node->next, NULL); if (next) break;
Since only the read is outside of critical sections, fixed it by adding a READ_ONCE().
Signed-off-by: Qian Cai <cai@lca.pw> --- kernel/locking/osq_lock.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/locking/osq_lock.c b/kernel/locking/osq_lock.c index 6ef600aa0f47..8f565165019a 100644 --- a/kernel/locking/osq_lock.c +++ b/kernel/locking/osq_lock.c @@ -77,7 +77,7 @@ osq_wait_next(struct optimistic_spin_queue *lock, */ if (node->next) { next = xchg(&node->next, NULL); - if (next) + if (READ_ONCE(next)) break; } -- 2.21.0 (Apple Git-122.2)
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