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

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Message-ID: <368c990c30c5bacde15ac4bce5db8389aea3ec9c.camel@intel.com>
Date:   Mon, 15 Nov 2021 22:35:23 +0000
From:   "Winiarska, Iwona" <iwona.winiarska@...el.com>
To:     "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
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        "Williams, Dan J" <dan.j.williams@...el.com>
Subject: Re: [PATCH v3 06/13] peci: Add device detection

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?

Thanks
-Iwona

> 
> thanks,
> 
> greg k-h