From: Hao Xu <haoxu@linux.alibaba.com>
To: Jens Axboe <axboe@kernel.dk>
Cc: io-uring@vger.kernel.org, Pavel Begunkov <asml.silence@gmail.com>,
Joseph Qi <joseph.qi@linux.alibaba.com>
Subject: Re: [PATCH 3/4] io-wq: fix worker->refcount when creating worker in work exit
Date: Sun, 12 Sep 2021 17:04:15 +0800 [thread overview]
Message-ID: <e84feefc-7c71-a55c-1463-e74d800162d9@linux.alibaba.com> (raw)
In-Reply-To: <e9ca65e1-46d7-de2d-e897-8cb3393c88f2@kernel.dk>
在 2021/9/12 上午6:13, Jens Axboe 写道:
> 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 <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);
>
> 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().
Doesn't see the relationship between worker->flags and the creation.
But yes, the creation path does io_worker_get() which causes failure
if it's from io_worker_exit(), Now I understand it is more like a
feature, isn't it? Anyway, the issue in 4/4 seems still there.
Regards,
Hao
>
next prev parent reply other threads:[~2021-09-12 9:04 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
2021-09-12 9:04 ` Hao Xu [this message]
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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