[PATCH 3/4] io-wq: fix worker->refcount when creating worker in work exit

[Hao Xu <haoxu@linux.alibaba.com>]

We may enter the worker creation path from io_worker_exit(), and
refcount is already zero, which causes definite failure of worker
creation.
io_worker_exit
                              ref = 0
->io_wqe_dec_running
  ->io_queue_worker_create
    ->io_worker_get           failure since ref is 0

Signed-off-by: Hao Xu <haoxu@linux.alibaba.com>
---
 fs/io-wq.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/io-wq.c b/fs/io-wq.c
index 0e1288a549eb..75e79571bdfd 100644
--- a/fs/io-wq.c
+++ b/fs/io-wq.c
@@ -188,7 +188,9 @@ static void io_worker_exit(struct io_worker *worker)
 	list_del_rcu(&worker->all_list);
 	acct->nr_workers--;
 	preempt_disable();
+	refcount_set(&worker->ref, 1);
 	io_wqe_dec_running(worker);
+	refcount_set(&worker->ref, 0);
 	worker->flags = 0;
 	current->flags &= ~PF_IO_WORKER;
 	preempt_enable();
-- 
2.24.4