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From: Jens Axboe <[email protected]>
To: Hao Xu <[email protected]>
Cc: [email protected], Pavel Begunkov <[email protected]>,
	Joseph Qi <[email protected]>
Subject: Re: [PATCH 3/4] io-wq: fix worker->refcount when creating worker in work exit
Date: Sat, 11 Sep 2021 16:13:56 -0600	[thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>

On 9/11/21 1:40 PM, Hao Xu wrote:
> 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 <[email protected]>
> ---
>  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);

That kind of refcount manipulation is highly suspect. And in fact it
should not be needed, io_worker_exit() clears ->flags before going on
with worker teardown. Hence you can't hit worker creation from
io_wqe_dec_running().

-- 
Jens Axboe


  reply	other threads:[~2021-09-11 22:13 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-11 19:40 [PATCH 0/4] iowq fix Hao Xu
2021-09-11 19:40 ` [PATCH 1/4] io-wq: tweak return value of io_wqe_create_worker() Hao Xu
2021-09-12 18:10   ` Jens Axboe
2021-09-12 19:02     ` Hao Xu
2021-09-12 21:34       ` Jens Axboe
2021-09-13  6:37         ` Hao Xu
2021-09-11 19:40 ` [PATCH 2/4] io-wq: code clean " Hao Xu
2021-09-12 18:18   ` Jens Axboe
2021-09-13  8:30   ` Hao Xu
2021-09-11 19:40 ` [PATCH 3/4] io-wq: fix worker->refcount when creating worker in work exit Hao Xu
2021-09-11 22:13   ` Jens Axboe [this message]
2021-09-12  9:04     ` Hao Xu
2021-09-12 18:07       ` Jens Axboe
2021-09-11 19:40 ` [PATCH 4/4] io-wq: fix potential race of acct->nr_workers Hao Xu
2021-09-12 18:23   ` Jens Axboe

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