linux-kernel - Re: [BUG] Deferred probing in driver model is racy, resulting in lost probes

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Message-ID: <20120926202321.GD30938@n2100.arm.linux.org.uk>
Date:	Wed, 26 Sep 2012 21:23:21 +0100
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	Ming Lei <tom.leiming@...il.com>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Grant Likely <grant.likely@...retlab.ca>,
	Arnd Bergmann <arnd@...db.de>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>
Subject: Re: [BUG] Deferred probing in driver model is racy, resulting in
	lost probes

On Wed, Sep 26, 2012 at 01:08:33PM -0700, Greg Kroah-Hartman wrote:
> On Sun, Sep 16, 2012 at 09:24:43PM +0800, Ming Lei wrote:
> > diff --git a/drivers/base/bus.c b/drivers/base/bus.c
> > index 181ed26..17d7437 100644
> > --- a/drivers/base/bus.c
> > +++ b/drivers/base/bus.c
> > @@ -714,12 +714,12 @@ int bus_add_driver(struct device_driver *drv)
> >  	if (error)
> >  		goto out_unregister;
> > 
> > +	klist_add_tail(&priv->knode_bus, &bus->p->klist_drivers);
> >  	if (drv->bus->p->drivers_autoprobe) {
> >  		error = driver_attach(drv);
> >  		if (error)
> >  			goto out_unregister;
> >  	}
> > -	klist_add_tail(&priv->knode_bus, &bus->p->klist_drivers);
> >  	module_add_driver(drv->owner, drv);
> > 
> >  	error = driver_create_file(drv, &driver_attr_uevent);
> > 
> > 
> > 
> 
> Did the above patch ever prove to solve the issue or not?

To be honest, I've not bothered to test the above patch, and now when I
look at it, I notice it's broken - in that on error it will corrupt the
driver list.  Take a look at the error path.

priv is drv->p.  We add priv->knode_bus to the driver list.  If
driver_attach() returns an error, then we go to out_unregister, which
does:

out_unregister:
        kobject_put(&priv->kobj);
        kfree(drv->p);
        drv->p = NULL;

thereby freeing the node we just added to the driver list without first
removing it.

I suspect it will fix the problem, but let's get the patch to be correct
before it gets tested...
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