[PATCH v2 4/7] blk-mq: Introduce blk_quiesce_queue() and blk_resume_queue()

[Bart Van Assche]

On 10/04/16 21:32, Ming Lei wrote:
> On Wed, Oct 5, 2016 at 12:16 PM, Bart Van Assche
> <bart.vanassche at sandisk.com> wrote:
>> On 10/01/16 15:56, Ming Lei wrote:
>>>
>>> If we just call the rcu/srcu read lock(or the mutex) around .queue_rq(),
>>> the above code needn't to be duplicated any more.
>>
>> Can you have a look at the attached patch? That patch uses an srcu read lock
>> for all queue types, whether or not the BLK_MQ_F_BLOCKING flag has been set.
>
> That is much cleaner now.
>
>> Additionally, I have dropped the QUEUE_FLAG_QUIESCING flag. Just like
>> previous versions, this patch has been tested.
>
> I think the flag of QUEUE_FLAG_QUIESCING is still needed because we
> have to set this flag to prevent new coming .queue_rq() from being run,
> and synchronize_srcu() won't wait for completion of that at all (see
> section of 'Update-Side Primitives' in [1]).
>
> [1] https://lwn.net/Articles/202847/

Hello Ming,

How about using the existing flag BLK_MQ_S_STOPPED instead of 
introducing a new QUEUE_FLAG_QUIESCING flag? From the comment above 
blk_mq_quiesce_queue() in the patch that was attached to my previous 
e-mail: "Additionally, it is not prevented that new queue_rq() calls 
occur unless the queue has been stopped first."

Thanks,

Bart.