linux-kernel - Re: [driver-core PATCH v8 2/9] driver core: Establish order of operations for device_add and device

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Message-ID: <00810f93b199c524378b5c963d49bd798c5d9843.camel@linux.intel.com>
Date:   Mon, 10 Dec 2018 14:24:10 -0800
From:   Alexander Duyck <alexander.h.duyck@...ux.intel.com>
To:     Dan Williams <dan.j.williams@...el.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        "Luis R. Rodriguez" <mcgrof@...nel.org>,
        linux-nvdimm <linux-nvdimm@...ts.01.org>,
        Tejun Heo <tj@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux-pm mailing list <linux-pm@...r.kernel.org>,
        jiangshanlai@...il.com, "Rafael J. Wysocki" <rafael@...nel.org>,
        "Brown, Len" <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
        zwisler@...nel.org, Dave Jiang <dave.jiang@...el.com>,
        bvanassche@....org
Subject: Re: [driver-core PATCH v8 2/9] driver core: Establish order of
 operations for device_add and device_del via bitflag

On Mon, 2018-12-10 at 13:23 -0800, Dan Williams wrote:
> On Mon, Dec 10, 2018 at 1:15 PM Dan Williams <dan.j.williams@...el.com> wrote:
> > 
> > On Mon, Dec 10, 2018 at 12:58 PM Alexander Duyck
> > <alexander.h.duyck@...ux.intel.com> wrote:
> 
> [..]
> > > Also the context for the two functions seems to be a bit different. In
> > > the case of __device_attach_driver the device_lock is already held. In
> > > __driver_attach the lock on the device isn't taken until after a match
> > > has been found.
> > 
> > Yes, I was only pattern matching when looking at the context of where
> > dev->dead is checked in __driver_attach() and wondering why it was
> > checked outside of __device_attach_driver()
> 
> ...and now I realize the bigger point of your concern, we need to
> check dev->dead after acquiring the device_lock otherwise the race is
> back. We can defer that consolidation, but the larger concern of
> making it internal to __device_attach_driver() still stands.

I'm still not a fan of moving it into __device_attach_driver. I would
much rather pull out the dev->driver check and instead place that in
__device_attach_async_helper.

The __device_attach function as I said took the device_lock and had
already checked dev->driver. So in the non-async path it shouldn't be
possible for dev->driver to ever be set anyway. In addition
__device_attach_driver is called once for each driver on a given bus,
so dropping the test should reduce driver load time since it is one
less test that has to be performed per driver.