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

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Message-ID: <KL1P15301MB00062308DD0D900D9A8943FDBF6D0@KL1P15301MB0006.APCP153.PROD.OUTLOOK.COM>
Date:   Tue, 29 May 2018 21:28:27 +0000
From:   Dexuan Cui <decui@...rosoft.com>
To:     Andy Shevchenko <andy.shevchenko@...il.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

> From: Andy Shevchenko <andy.shevchenko@...il.com>
> Sent: Tuesday, May 29, 2018 14:21
> 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);
> 
> ?
Thanks for the suggestion, Andy!
The coding style you suggested looks better to me. :-)

> > +       if (!ret)
> > +               ret = wait_for_response(hdev, &comp);
> 
> Better to use well established patterns, i.e.
> 
> if (ret)
>  return ret;
Agreed.

> 
> > +               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

I'll try to send out a patch to improve the coding style, after I address
Michael Kelley's concern of a race.

Thanks,
-- Dexuan