linux-kernel - Re: [PATCH V2 rdma-next 2/3] RDMA/hns: Fix the chip hanging caused by sending mailbox&CMQ during reset

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Date:   Tue, 29 Jan 2019 10:18:40 +0800
From:   "Wei Hu (Xavier)" <xavier.huwei@...wei.com>
To:     Jason Gunthorpe <jgg@...pe.ca>
CC:     <dledford@...hat.com>, <linux-rdma@...r.kernel.org>,
        <lijun_nudt@....com>, <oulijun@...wei.com>,
        <liudongdong3@...wei.com>, <linuxarm@...wei.com>,
        <linux-kernel@...r.kernel.org>, <xavier_huwei@....com>
Subject: Re: [PATCH V2 rdma-next 2/3] RDMA/hns: Fix the chip hanging caused by
 sending mailbox&CMQ during reset



On 2019/1/29 2:27, Jason Gunthorpe wrote:
> On Sat, Jan 26, 2019 at 09:47:42AM +0800, Wei Hu (Xavier) wrote:
>>
>> On 2019/1/26 5:50, Jason Gunthorpe wrote:
>>> On Fri, Jan 25, 2019 at 10:15:40AM +0800, Wei Hu (Xavier) wrote:
>>>> On 2019/1/25 2:31, Jason Gunthorpe wrote:
>>>>> On Thu, Jan 24, 2019 at 11:13:29AM +0800, Wei Hu (Xavier) wrote:
>>>>>> On 2019/1/24 6:40, Jason Gunthorpe wrote:
>>>>>>> On Sat, Jan 19, 2019 at 11:36:06AM +0800, Wei Hu (Xavier) wrote:
>>>>>>>
>>>>>>>> +static int hns_roce_v2_cmd_hw_resetting(struct hns_roce_dev *hr_dev,
>>>>>>>> +					unsigned long instance_stage,
>>>>>>>> +					unsigned long reset_stage)
>>>>>>>> +{
>>>>>>>> +	struct hns_roce_v2_priv *priv = (struct hns_roce_v2_priv *)hr_dev->priv;
>>>>>>>> +	struct hnae3_handle *handle = priv->handle;
>>>>>>>> +	const struct hnae3_ae_ops *ops = handle->ae_algo->ops;
>>>>>>>> +	unsigned long end;
>>>>>>>> +
>>>>>>>> +	/* When hardware reset is detected, we should stop sending mailbox&cmq
>>>>>>>> +	 * to hardware, and wait until hardware reset finished. If now
>>>>>>>> +	 * in .init_instance() function, we should exit with error. If now at
>>>>>>>> +	 * HNAE3_INIT_CLIENT stage of soft reset process, we should exit with
>>>>>>>> +	 * error, and then HNAE3_INIT_CLIENT related process can rollback the
>>>>>>>> +	 * operation like notifing hardware to free resources, HNAE3_INIT_CLIENT
>>>>>>>> +	 * related process will exit with error to notify NIC driver to
>>>>>>>> +	 * reschedule soft reset process once again.
>>>>>>>> +	 */
>>>>>>>> +	end = msecs_to_jiffies(HNS_ROCE_V2_HW_RST_TIMEOUT) + jiffies;
>>>>>>>> +	while (ops->get_hw_reset_stat(handle) && time_before(jiffies, end))
>>>>>>>> +		udelay(1);
>>>>>>> I thought you were getting rid of these loops?
>>>>>> Hi, Jason
>>>>>>
>>>>>>     Upper applications maybe notify driver to issue mailbox or CMD
>>>>>>     commands to hardware, some commands used to cancel resources,
>>>>>>     destory bt/destory cq/unreg mr/destory qp etc. when such
>>>>>>     commands are executed successfully, the hardware engine will
>>>>>>     no longer access some memory registered by the driver.
>>>>>>
>>>>>>     When reset occurs, it is possible for upper applications notify driver
>>>>>>     to issue mailbox or CMD commands, we need to wait until hardware
>>>>>>     reset finished to ensure that hardware no longer accesses related
>>>>>> memory.
>>>>> You should not wait for things using loops like the above.
>>>> Hi, Jason
>>>>
>>>>     Are your comments foucsing on udelay? If not, thanks for your detail
>>>> information.
>>>>     In hns3 RoCE driver, some CMQ/mailbox operation are called inside
>>>> the lock,
>>>>     we can't use msleep in the lock, otherwise it will cause deadlock.
>>>>     When reset occurs, RDMA service cannot be provided normally, I think
>>>> in this
>>>>     case using udelay will not have a great impact.
>>> You should not use any kind of sleep call in a loop like this.
>> Hi, Jason
>>
>>     OK, I got your opinion and will modify it in v3 patch as below:   
>>
>>     end = msecs_to_jiffies(HNS_ROCE_V2_HW_RST_TIMEOUT) + jiffies;
>>     while (time_before(jiffies, end))
>>         if (!ops->get_hw_reset_stat(handle))
>>             break;           
> You shouldn't be looping like this at all, a busy loop is worse, don't
> try and open code spinlocks.
Hi, Jason
   
        OK,  we will modify some places calling CMQ/mailbox operation,
        replace spinlock with mutex, and add msleep here:

    end = msecs_to_jiffies(HNS_ROCE_V2_HW_RST_TIMEOUT) + jiffies;
    while (time_before(jiffies, end)) {
        if (!ops->get_hw_reset_stat(handle))
            break;
	msleep(20); 
    }

    Thanks for your comments. 

    Regards
Xavier
> Jason
>
> .
>