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:   Sun, 3 Feb 2019 20:46:40 +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 11:45, Jason Gunthorpe wrote:
> On Tue, Jan 29, 2019 at 10:18:40AM +0800, Wei Hu (Xavier) wrote:
>>
>> 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); 
>>     }
> How many more times do I have to say not to code spin loops like
> this???? Use proper locking!
Hi, Jason
    Ok,  Thanks for your comments.
    And we removed the loop operation here and sent patch v4. Thanks

    Regards
Xavier
> Jason
>
> .
>