Date:   Tue, 16 Nov 2021 07:26:28 +0100
From:   "gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>
To:     "Winiarska, Iwona" <iwona.winiarska@intel.com>
Cc:     "corbet@lwn.net" <corbet@lwn.net>,
        "jae.hyun.yoo@linux.intel.com" <jae.hyun.yoo@linux.intel.com>,
        "linux-hwmon@vger.kernel.org" <linux-hwmon@vger.kernel.org>,
        "andrew@aj.id.au" <andrew@aj.id.au>,
        "Luck, Tony" <tony.luck@intel.com>,
        "Hansen, Dave" <dave.hansen@intel.com>,
        "d.mueller@elsoft.ch" <d.mueller@elsoft.ch>,
        "jdelvare@suse.com" <jdelvare@suse.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "olof@lixom.net" <olof@lixom.net>,
        "rdunlap@infradead.org" <rdunlap@infradead.org>,
        "devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
        "linux-aspeed@lists.ozlabs.org" <linux-aspeed@lists.ozlabs.org>,
        "linux-doc@vger.kernel.org" <linux-doc@vger.kernel.org>,
        "arnd@arndb.de" <arnd@arndb.de>,
        "linux@roeck-us.net" <linux@roeck-us.net>,
        "zweiss@equinix.com" <zweiss@equinix.com>,
        "robh+dt@kernel.org" <robh+dt@kernel.org>,
        "openbmc@lists.ozlabs.org" <openbmc@lists.ozlabs.org>,
        "bp@alien8.de" <bp@alien8.de>, "joel@jms.id.au" <joel@jms.id.au>,
        "linux-arm-kernel@lists.infradead.org" 
        <linux-arm-kernel@lists.infradead.org>,
        "pierre-louis.bossart@linux.intel.com" 
        <pierre-louis.bossart@linux.intel.com>,
        "andriy.shevchenko@linux.intel.com" 
        <andriy.shevchenko@linux.intel.com>,
        "Williams, Dan J" <dan.j.williams@intel.com>
Subject: Re: [PATCH v3 06/13] peci: Add device detection
Message-ID: <YZNPFGPXfCLfJMq3@kroah.com>
References: <20211115182552.3830849-1-iwona.winiarska@intel.com>
 <20211115182552.3830849-7-iwona.winiarska@intel.com>
 <YZKr1Rqfx6Cmw+Ok@kroah.com>
 <368c990c30c5bacde15ac4bce5db8389aea3ec9c.camel@intel.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=iso-8859-1
Content-Disposition: inline
Content-Transfer-Encoding: 8bit
In-Reply-To: <368c990c30c5bacde15ac4bce5db8389aea3ec9c.camel@intel.com>
Precedence: bulk

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