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

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Message-ID: <CACVXFVPnpQ6yHiDaoo_CPG7oSEq+ZzxpmTgQv55-tRRyaavDfA@mail.gmail.com>
Date:	Thu, 27 Sep 2012 07:47:46 +0800
From:	Ming Lei <tom.leiming@...il.com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	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 Thu, Sep 27, 2012 at 4:23 AM, Russell King - ARM Linux
<linux@....linux.org.uk> wrote:
> 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

In fact, driver_attach() always returns zero, so it does __not__ affect
your test.

I knew the failure shouldn't be handled in theory because the probe
failure on one device should not cause failure of driver_register, and
it should be fixed, IMO.

> 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...

Trust me, please go ahead to test and it doesn't affect it...

Thanks,
-- 
Ming Lei
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