linux-kernel - Re: [PATCH v3 06/13] peci: Add device detection

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Message-ID: <YZNPFGPXfCLfJMq3@kroah.com>
Date:   Tue, 16 Nov 2021 07:26:28 +0100
From:   "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
To:     "Winiarska, Iwona" <iwona.winiarska@...el.com>
Cc:     "corbet@....net" <corbet@....net>,
        "jae.hyun.yoo@...ux.intel.com" <jae.hyun.yoo@...ux.intel.com>,
        "linux-hwmon@...r.kernel.org" <linux-hwmon@...r.kernel.org>,
        "andrew@...id.au" <andrew@...id.au>,
        "Luck, Tony" <tony.luck@...el.com>,
        "Hansen, Dave" <dave.hansen@...el.com>,
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        <pierre-louis.bossart@...ux.intel.com>,
        "andriy.shevchenko@...ux.intel.com" 
        <andriy.shevchenko@...ux.intel.com>,
        "Williams, Dan J" <dan.j.williams@...el.com>
Subject: Re: [PATCH v3 06/13] peci: Add device detection

On Mon, Nov 15, 2021 at 10:35:23PM +0000, Winiarska, Iwona wrote:
> On Mon, 2021-11-15 at 19:49 +0100, Greg Kroah-Hartman wrote:
> > On Mon, Nov 15, 2021 at 07:25:45PM +0100, Iwona Winiarska wrote:
> > > +void peci_device_destroy(struct peci_device *device)
> > > +{
> > > +       bool killed;
> > > +
> > > +       device_lock(&device->dev);
> > > +       killed = kill_device(&device->dev);
> > 
> > Eeek, why call this?
> > 
> > > +       device_unlock(&device->dev);
> > > +
> > > +       if (!killed)
> > > +               return;
> > 
> > What happened if something changed after you unlocked it?
> 
> We either killed it, or the other caller killed it.
> 
> > 
> > Why is kill_device() required at all?  That's a very rare function to
> > call, and one that only one "bus" calls today because it is very
> > special (i.e. crazy and broken...)
> 
> It's used to avoid double-delete in case of races between peci_controller
> unregister and "manually" removing the device using sysfs (pointed out by Dan in
> v2). We're calling peci_device_destroy() in both callsites.
> Other way to solve it would be to just have a peci-specific lock, but
> kill_device seemed to be well suited for the problem at hand.
> Do you suggest to remove it and just go with the lock?

Yes please, remove it and use the lock.

Also, why are you required to have a sysfs file that can remove the
device?  Who wants that?

thanks,

greg k-h