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

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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: Hao Xu <haoxu@linux.alibaba.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Hao Xu 2021-09-12 03:40:52 +08:00 committed by Jens Axboe
parent 7a842fb589
commit 767a65e9f3
1 changed files with 1 additions and 2 deletions
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3
fs/io-wq.c
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@ -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;