Re: [PATCH 1/2] io-wq: fix bug of creating io-wokers unconditionally

[Hao Xu <haoxu@linux.alibaba.com>]

在 2021/8/9 下午10:18, Jens Axboe 写道:
> On 8/9/21 8:08 AM, Hao Xu wrote:
>> 在 2021/8/9 下午10:01, Jens Axboe 写道:
>>> On 8/8/21 7:54 AM, Hao Xu wrote:
>>>> The former patch to add check between nr_workers and max_workers has a
>>>> bug, which will cause unconditionally creating io-workers. That's
>>>> because the result of the check doesn't affect the call of
>>>> create_io_worker(), fix it by bringing in a boolean value for it.
>>>>
>>>> Fixes: 21698274da5b ("io-wq: fix lack of acct->nr_workers < acct->max_workers judgement")
>>>> Signed-off-by: Hao Xu <haoxu@linux.alibaba.com>
>>>> ---
>>>>    fs/io-wq.c | 19 ++++++++++++++-----
>>>>    1 file changed, 14 insertions(+), 5 deletions(-)
>>>>
>>>> diff --git a/fs/io-wq.c b/fs/io-wq.c
>>>> index 12fc19353bb0..5536b2a008d1 100644
>>>> --- a/fs/io-wq.c
>>>> +++ b/fs/io-wq.c
>>>> @@ -252,14 +252,15 @@ static void io_wqe_wake_worker(struct io_wqe *wqe, struct io_wqe_acct *acct)
>>>>    
>>>>    		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)
>>>> +		if (do_create) {
>>>> +			atomic_inc(&acct->nr_running);
>>>> +			atomic_inc(&wqe->wq->worker_refs);
>>>>    			create_io_worker(wqe->wq, wqe, acct->index);
>>>> +		}
>>>>    	}
>>>
>>> I don't get this hunk - we already know we're creating a worker, what's the
>>> point in moving the incs?
>>>
>> Actually not much difference, I think we don't need to protect
>> nr_running and worker_refs by wqe->lock, so narrow the range of
>> raw_spin_lock_irq - raw_spin_unlock_irq
> 
> Agree, we don't need it, but it's not a fix as such. I'd rather defer that
> one to a separate cleanup for the next release.
I'll send it later.
>