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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Message-ID: <20190128182759.GA25106@ziepe.ca>
Date:   Mon, 28 Jan 2019 11:27:59 -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 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.

Jason