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10:01, 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