Re: [PATCH 2/2] blk-mq: simplify queue mapping & schedule with each possisble CPU

[Christian Borntraeger]

On 01/17/2018 11:07 AM, Christian Borntraeger wrote:
> 
> 
> On 01/17/2018 10:57 AM, Ming Lei wrote:
>> Hi Jianchao,
>>
>> On Wed, Jan 17, 2018 at 04:09:11PM +0800, jianchao.wang wrote:
>>> Hi ming 
>>>
>>> Thanks for your kindly response.
>>>
>>> On 01/17/2018 02:22 PM, Ming Lei wrote:
>>>> This warning can't be removed completely, for example, the CPU figured
>>>> in blk_mq_hctx_next_cpu(hctx) can be put on again just after the
>>>> following call returns and before __blk_mq_run_hw_queue() is scheduled
>>>> to run.
>>>>
>>>> 	kblockd_mod_delayed_work_on(blk_mq_hctx_next_cpu(hctx), &hctx->run_work, msecs_to_jiffies(msecs))
>>> We could use cpu_active in __blk_mq_run_hw_queue() to narrow the window.
>>> There is a big gap between cpu_online and cpu_active. rebind_workers is also between them.
>>
>> This warning is harmless, also you can't reproduce it without help of your
>> special patch, I guess, :-) So the window shouldn't be a big deal. 
> 
> FWIW, every WARN_ON is problematic since there are people running with panic_on_warn.

To make it more clear. Every WARN_ON that can happen in real life without actually being
an error is problematic.

> If a condition can happen we should not use WARN_ON but something else.
>