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:   Thu, 24 Jan 2019 11:31:20 -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 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.

Jason