[PATCH v2] nvmet: Don't queue fatal error work if csts.cfs is set

[Sagi Grimberg]

>>  void nvmet_ctrl_fatal_error(struct nvmet_ctrl *ctrl)
>>  {
>> -	ctrl->csts |= NVME_CSTS_CFS;
>> -	INIT_WORK(&ctrl->fatal_err_work, nvmet_fatal_error_handler);
>> -	schedule_work(&ctrl->fatal_err_work);
>> +	mutex_lock(&ctrl->lock);
>> +	if (!(ctrl->csts & NVME_CSTS_CFS)) {
>> +		ctrl->csts |= NVME_CSTS_CFS;
>> +		INIT_WORK(&ctrl->fatal_err_work,
>> nvmet_fatal_error_handler);
>> +		schedule_work(&ctrl->fatal_err_work);
>> +	}
>> +	mutex_unlock(&ctrl->lock);
>
> Surrounding the mutex_lock()/unlock() around the if() is definitely
> safer and a more conservative, but I would think it would be OK to
> stick the mutex_lock/unlock() within the if() statement (mutex_lock()
> as the first line after the if() check, mutex_unlock() as the last line
> of the if()), as trying to acquire a lock before checking the condition
> to see if CFS needs to be set is sub-optimal.

I don't think this is worth optimizing, it is error flow after all..