linux-kernel - Re: [PATCH rdma-rc 1/3] RDMA/hns: Fix the Oops during rmmod or insmod ko when reset occurs

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Date:   Mon, 14 Jan 2019 15:06:55 -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,
        liuyixian@...wei.com, zhangxiping3@...wei.com, linuxarm@...wei.com,
        linux-kernel@...r.kernel.org, xavier_huwei@....com
Subject: Re: [PATCH rdma-rc 1/3] RDMA/hns: Fix the Oops during rmmod or
 insmod ko when reset occurs

On Sat, Jan 12, 2019 at 03:55:31PM +0800, Wei Hu (Xavier) wrote:
> 
> 
> On 2019/1/12 5:34, Jason Gunthorpe wrote:
> > On Thu, Jan 10, 2019 at 09:57:41PM +0800, Wei Hu (Xavier) wrote:
> >> +	/* Check the status of the current software reset process, if in
> >> +	 * software reset process, wait until software reset process finished,
> >> +	 * in order to ensure that reset process and this function will not call
> >> +	 * __hns_roce_hw_v2_uninit_instance at the same time.
> >> +	 * If a timeout occurs, it indicates that the network subsystem has
> >> +	 * encountered a serious error and cannot be recovered from the reset
> >> +	 * processing.
> >> +	 */
> >> +	if (ops->ae_dev_resetting(handle)) {
> >> +		dev_warn(dev, "Device is busy in resetting state. waiting.\n");
> >> +		end = msecs_to_jiffies(HNS_ROCE_V2_RST_PRC_MAX_TIME) + jiffies;
> >> +		while (ops->ae_dev_resetting(handle) &&
> >> +		       time_before(jiffies, end))
> >> +			msleep(20);
> > Really? Does this have to be so ugly? Why isn't there just a simple
> > lock someplace that is held during reset?
> >
> > I'm skeptical that all this strange looking stuff is properly locked
> > and concurrency safe.
> Hi, Jason
> 
> The hns3 NIC driver notifies the hns RoCE driver to perform
> reset related processing by calling the .reset_notify() interface
> registered by the RoCE driver.
> 
> There is a constraint on the hip08 chip, the NIC driver needs to
> stop the flow before hardware startup reset, otherwise the chip
> may hang up.
> 
> We've also thought about using locks, but found using locks can
> lead to more serious problems because of that restriction of the
> chip.
> If using locks here, reset processing may wait for uninstallation
> to complete, this may lead that NIC driver fails to stop the flow
> in time in the reset process, thus causing the chip to hang up.

If you are sleeping then I'm sure a lock can be used instead, how
would it be any different?

Jason