linux-kernel - Re: [PATCH] PCI: hv: Do not wait forever on a device that has disappeared

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Message-ID: <CAHp75Vd9kiyOaSbaK6c4b7ucF23kgP0yQxKpUAGrjHgKfJprXA@mail.gmail.com>
Date:   Wed, 30 May 2018 00:20:57 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Dexuan Cui <decui@...rosoft.com>
Cc:     Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        KY Srinivasan <kys@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        "olaf@...fle.de" <olaf@...fle.de>,
        "apw@...onical.com" <apw@...onical.com>,
        "jasowang@...hat.com" <jasowang@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "driverdev-devel@...uxdriverproject.org" 
        <driverdev-devel@...uxdriverproject.org>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        "vkuznets@...hat.com" <vkuznets@...hat.com>,
        "marcelo.cerri@...onical.com" <marcelo.cerri@...onical.com>
Subject: Re: [PATCH] PCI: hv: Do not wait forever on a device that has disappeared

On Thu, May 24, 2018 at 12:12 AM, Dexuan Cui <decui@...rosoft.com> wrote:
>
> Before the guest finishes the device initialization, the device can be
> removed anytime by the host, and after that the host won't respond to
> the guest's request, so the guest should be prepared to handle this
> case.

> +       while (true) {
> +               if (hdev->channel->rescind) {
> +                       dev_warn_once(&hdev->device, "The device is gone.\n");
> +                       return -ENODEV;
> +               }
> +
> +               if (wait_for_completion_timeout(comp, HZ / 10))
> +                       break;
> +       }

Infinite loops are usually a red flags.

What's wrong with simple:

do {
  ...
} while (wait_...(...) == 0);

?

> +       if (!ret)
> +               ret = wait_for_response(hdev, &comp);

Better to use well established patterns, i.e.

if (ret)
 return ret;

> +               if (!ret)
> +                       ret = wait_for_response(hdev, &comp_pkt.host_event);

Here it looks okay on the first glance, but better to think about it
again and refactor.

-- 
With Best Regards,
Andy Shevchenko