Re: [PATCH 1/4] io-wq: tweak return value of io_wqe_create_worker()

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

在 2021/9/13 上午2:10, Jens Axboe 写道:
> On 9/11/21 1:40 PM, Hao Xu wrote:
>> The return value of io_wqe_create_worker() should be false if we cannot
>> create a new worker according to the name of this function.
>>
>> Signed-off-by: Hao Xu <haoxu@linux.alibaba.com>
>> ---
>>   fs/io-wq.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/fs/io-wq.c b/fs/io-wq.c
>> index 382efca4812b..1b102494e970 100644
>> --- a/fs/io-wq.c
>> +++ b/fs/io-wq.c
>> @@ -267,7 +267,7 @@ static bool io_wqe_create_worker(struct io_wqe *wqe, struct io_wqe_acct *acct)
>>   		return create_io_worker(wqe->wq, wqe, acct->index);
>>   	}
>>   
>> -	return true;
>> +	return false;
>>   }
> 
> I think this is just a bit confusing. It's not an error case, we just
> didn't need to create a worker. So don't return failure, or the caller
> will think that we failed while we did not.
hmm, I think it is an error case----'we failed to create a new worker
since nr_worker == max_worker'. nr_worker == max_worker doesn't mean
'no need', we may meet situation describled in 4/4: max_worker is 1,
currently 1 worker is running, and we return true here:

           did_create = io_wqe_create_worker(wqe, acct);

              //*******nr_workers changes******//

           if (unlikely(!did_create)) {
                   raw_spin_lock(&wqe->lock);
                   /* fatal condition, failed to create the first worker */
                   if (!acct->nr_workers) {
                           raw_spin_unlock(&wqe->lock);
                           goto run_cancel;
                   }
                   raw_spin_unlock(&wqe->lock);
           }

we will miss the next check, but we have to do the check, since
number of workers may decrease to 0 in //******// place.

or maybe we can see the return value as 'do we create a new worker or
not', and the next code do safe check if it is false.
>