Hi Tejun,
2015-09-27 2:32 GMT+09:00 Tejun Heo <t...@kernel.org>:
> Hello,
>
> On Sun, Sep 27, 2015 at 02:09:24AM +0900, Akinobu Mita wrote:
>> @@ -420,7 +420,9 @@ static void blk_mq_sysfs_init(struct request_queue *q)
>> /* see blk_register_queue() */
>> void blk_mq_finish_init(struct request_queue *q)
>> {
>> + mutex_lock(&q->mq_freeze_lock);
>> percpu_ref_switch_to_percpu(&q->mq_usage_counter);
>> + mutex_unlock(&q->mq_freeze_lock);
>
> This looks weird to me. What can it race against at this point?
The possible scenario is described in commit log (1. ~ 7.). In summary,
blk_mq_finish_init() and blk_mq_freeze_queue_start() can be executed
at the same time, so this is required to serialize the execution of
percpu_ref_switch_to_percpu() by blk_mq_finish_init() and
percpu_ref_kill() by blk_mq_freeze_queue_start().
>> @@ -115,11 +115,15 @@ void blk_mq_freeze_queue_start(struct request_queue *q)
>> {
>> int freeze_depth;
>>
>> + mutex_lock(&q->mq_freeze_lock);
>> +
>> freeze_depth = atomic_inc_return(&q->mq_freeze_depth);
>
> It doesn't have to be an atomic anymore, right?
Yes, you are right. I would like to make it in another patch in order to
simplify each change.
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