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:   Mon, 28 Jan 2019 20:45:05 -0700
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     "Wei Hu (Xavier)" <xavier.huwei@...wei.com>
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 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!

Jason