linux-kernel - Re: [char-misc-next v2] mei: bus: fix device leak

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Message-ID: <2025063042-usual-acutely-0d3b@gregkh>
Date: Mon, 30 Jun 2025 14:54:57 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: "Usyskin, Alexander" <alexander.usyskin@...el.com>
Cc: "Abliyev, Reuven" <reuven.abliyev@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [char-misc-next v2] mei: bus: fix device leak

On Mon, Jun 30, 2025 at 11:27:14AM +0000, Usyskin, Alexander wrote:
> > Subject: Re: [char-misc-next v2] mei: bus: fix device leak
> > 
> > On Mon, Jun 30, 2025 at 10:52:08AM +0000, Usyskin, Alexander wrote:
> > > > Subject: Re: [char-misc-next v2] mei: bus: fix device leak
> > > >
> > > > On Tue, Jun 24, 2025 at 02:05:20PM +0300, Alexander Usyskin wrote:
> > > > > The bus rescan function creates bus devices for all clients.
> > > > > The fixup routine is executed on all devices, unneeded
> > > > > devices are removed and fully initialized once set
> > > > > is_added flag to 1.
> > > >
> > > > I don't understand why the mei bus is so special that it has to have
> > > > this type of flag, when no other bus has that for its devices.  The bus
> > > > code should know if the device has been properly added or not, if not,
> > > > then no release function can be called and the structure isn't even
> > > > viable to be used or touched at all.
> > > >
> > > > So why is this needed?
> > >
> > > It seems that is_added can be replaced by device_is_registered().
> > 
> > Again, why do you need to track that?
> > 
> > But yes, that should work, although using it is usually a sign that
> > something is a bit broken in the design.
> > 
> 
> Mei bus uses device_initialize() and device_add() pair.
> After device_initialize() there are different hooks and filters called,
> that may lead to dropping the device or adding with device_add().
> Thus, we should track if device_add() is called when destroying the device.
> Not sure if this can be re-architected to use device_register().

You don't need to use device_register() but perhaps stop it with the
"rescan the bus and attempt to add all devices again" logic that is in
mei_cl_bus_rescan()?  There's no need to call device_add() on a device
and then way later attempt to initialize it, right?

Just find any new devices that you don't already have on your list of
registered devices, and then only add/initialize them, should be a lot
simpler logic overall than what the code is currently doing.

greg k-h