Commit 767a65e9 authored by Hao Xu's avatar Hao Xu Committed by Jens Axboe
Browse files

io-wq: fix potential race of acct->nr_workers 



Given max_worker is 1, and we currently have 1 running and it is
exiting. There may be race like:
 io_wqe_enqueue                   worker1
                               no work there and timeout
                               unlock(wqe->lock)
 ->insert work
                               -->io_worker_exit
 lock(wqe->lock)
 ->if(!nr_workers) //it's still 1
 unlock(wqe->lock)
    goto run_cancel
                                  lock(wqe->lock)
                                  nr_workers--
                                  ->dec_running
                                    ->worker creation fails
                                  unlock(wqe->lock)

We enqueued one work but there is no workers, causes hung.

Signed-off-by: default avatarHao Xu <haoxu@linux.alibaba.com>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 7a842fb5

fs/io-wq.c

+1 −2
Original line number Diff line number Diff line
@@ -176,7 +176,6 @@ static void io_worker_ref_put(struct io_wq *wq) 
static void io_worker_exit(struct io_worker *worker)

{

	struct io_wqe *wqe = worker->wqe;

	struct io_wqe_acct *acct = io_wqe_get_acct(worker);



	if (refcount_dec_and_test(&worker->ref))

		complete(&worker->ref_done);
@@ -186,7 +185,6 @@ static void io_worker_exit(struct io_worker *worker) 
	if (worker->flags & IO_WORKER_F_FREE)

		hlist_nulls_del_rcu(&worker->nulls_node);

	list_del_rcu(&worker->all_list);

	acct->nr_workers--;

	preempt_disable();

	io_wqe_dec_running(worker);

	worker->flags = 0;
@@ -569,6 +567,7 @@ static int io_wqe_worker(void *data) 
		}

		/* timed out, exit unless we're the last worker */

		if (last_timeout && acct->nr_workers > 1) {

			acct->nr_workers--;

			raw_spin_unlock(&wqe->lock);

			__set_current_state(TASK_RUNNING);

			break;