Re: [PATCH v4 1/9] driver core: Don't let a device probe until it's ready

[Danilo Krummrich]

On Mon Apr 6, 2026 at 6:34 PM CEST, Marc Zyngier wrote:
> On Mon, 06 Apr 2026 15:41:08 +0100,
> Doug Anderson <dianders@xxxxxxxxxxxx> wrote:
>> 
>> Hi,
>> 
>> On Sun, Apr 5, 2026 at 11:32 PM Marc Zyngier <maz@xxxxxxxxxx> wrote:
>> >
>> > > +      * blocked those attempts. Now that all of the above initialization has
>> > > +      * happened, unblock probe. If probe happens through another thread
>> > > +      * after this point but before bus_probe_device() runs then it's fine.
>> > > +      * bus_probe_device() -> device_initial_probe() -> __device_attach()
>> > > +      * will notice (under device_lock) that the device is already bound.
>> > > +      */
>> > > +     dev_set_ready_to_probe(dev);
>> >
>> > I think this lacks some ordering properties that we should be allowed
>> > to rely on. In this case, the 'ready_to_probe' flag being set should
>> > that all of the data structures are observable by another CPU.
>> >
>> > Unfortunately, this doesn't seem to be the case, see below.
>> 
>> I agree. I think Danilo was proposing fixing this by just doing:
>> 
>> device_lock(dev);
>> dev_set_ready_to_probe(dev);
>> device_unlock(dev);
>> 
>> While that's a bit of an overkill, it also works I think. Do folks
>> have a preference for what they'd like to see in v5?
>
> It would work, but I find the construct rather obscure, and it implies
> that there is a similar lock taken on the read path. Looking at the
> code for a couple of minutes doesn't lead to an immediate clue that
> such lock is indeed taken on all read paths.

Why do you think this is obscure? As I mentioned in [1], the whole purpose of
dev_set_ready_to_probe() is to protect against a concurrent probe() attempt of
driver_attach() in __driver_probe_device(), while __driver_probe_device() is
protected by the device lock is by design.

[1] https://lore.kernel.org/driver-core/DHM5TCBT6GDE.EFG3IPRP99G7@xxxxxxxxxx/