Commit 3d4e4fac authored by Hao Xu's avatar Hao Xu Committed by Jens Axboe
Browse files

io-wq: fix no lock protection of acct->nr_worker 



There is an acct->nr_worker visit without lock protection. Think about
the case: two callers call io_wqe_wake_worker(), one is the original
context and the other one is an io-worker(by calling
io_wqe_enqueue(wqe, linked)), on two cpus paralelly, this may cause
nr_worker to be larger than max_worker.
Let's fix it by adding lock for it, and let's do nr_workers++ before
create_io_worker. There may be a edge cause that the first caller fails
to create an io-worker, but the second caller doesn't know it and then
quit creating io-worker as well:

say nr_worker = max_worker - 1
        cpu 0                        cpu 1
   io_wqe_wake_worker()          io_wqe_wake_worker()
      nr_worker < max_worker
      nr_worker++
      create_io_worker()         nr_worker == max_worker
         failed                  return
      return

But the chance of this case is very slim.

Fixes: 685fe7fe ("io-wq: eliminate the need for a manager thread")
Signed-off-by: default avatarHao Xu <haoxu@linux.alibaba.com>
[axboe: fix unconditional create_io_worker() call]
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 83d6c393

fs/io-wq.c

+17 −6
Original line number Diff line number Diff line
@@ -247,9 +247,18 @@ static void io_wqe_wake_worker(struct io_wqe *wqe, struct io_wqe_acct *acct) 
	ret = io_wqe_activate_free_worker(wqe);

	rcu_read_unlock();



	if (!ret && acct->nr_workers < acct->max_workers) {

	if (!ret) {

		bool do_create = false;



		raw_spin_lock_irq(&wqe->lock);

		if (acct->nr_workers < acct->max_workers) {

			atomic_inc(&acct->nr_running);

			atomic_inc(&wqe->wq->worker_refs);

			acct->nr_workers++;

			do_create = true;

		}

		raw_spin_unlock_irq(&wqe->lock);

		if (do_create)

			create_io_worker(wqe->wq, wqe, acct->index);

	}

}
@@ -635,6 +644,9 @@ static void create_io_worker(struct io_wq *wq, struct io_wqe *wqe, int index) 
		kfree(worker);

fail:

		atomic_dec(&acct->nr_running);

		raw_spin_lock_irq(&wqe->lock);

		acct->nr_workers--;

		raw_spin_unlock_irq(&wqe->lock);

		io_worker_ref_put(wq);

		return;

	}
@@ -650,9 +662,8 @@ static void create_io_worker(struct io_wq *wq, struct io_wqe *wqe, int index) 
	worker->flags |= IO_WORKER_F_FREE;

	if (index == IO_WQ_ACCT_BOUND)

		worker->flags |= IO_WORKER_F_BOUND;

	if (!acct->nr_workers && (worker->flags & IO_WORKER_F_BOUND))

	if ((acct->nr_workers == 1) && (worker->flags & IO_WORKER_F_BOUND))

		worker->flags |= IO_WORKER_F_FIXED;

	acct->nr_workers++;

	raw_spin_unlock_irq(&wqe->lock);

	wake_up_new_task(tsk);

}