linux-kernel - Re: [PATCH v10 2/5] driver core: don't always lock parent in shutdown

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Message-ID: <CA+-xHTEk_N6qE5w+hWxXfSMJLQ5tFROMVZnr5h2HUmrwEKVdNQ@mail.gmail.com>
Date: Wed, 2 Jul 2025 10:38:35 -0400
From: David Jeffery <djeffery@...hat.com>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Stuart Hayes <stuart.w.hayes@...il.com>, linux-kernel@...r.kernel.org, 
	"Rafael J . Wysocki" <rafael@...nel.org>, Martin Belanger <Martin.Belanger@...l.com>, 
	"Oliver O'Halloran" <oohall@...il.com>, Daniel Wagner <dwagner@...e.de>, Keith Busch <kbusch@...nel.org>, 
	Lukas Wunner <lukas@...ner.de>, Jeremy Allison <jallison@....com>, Jens Axboe <axboe@...com>, 
	Christoph Hellwig <hch@....de>, Sagi Grimberg <sagi@...mberg.me>, linux-nvme@...ts.infradead.org, 
	Nathan Chancellor <nathan@...nel.org>, Jan Kiszka <jan.kiszka@...mens.com>, 
	Bert Karwatzki <spasswolf@....de>
Subject: Re: [PATCH v10 2/5] driver core: don't always lock parent in shutdown

On Tue, Jul 1, 2025 at 5:03 AM Greg Kroah-Hartman
<gregkh@...uxfoundation.org> wrote:
>
> On Wed, Jun 25, 2025 at 03:18:50PM -0500, Stuart Hayes wrote:
> > Don't lock a parent device unless it is needed in device_shutdown. This
> > is in preparation for making device shutdown asynchronous, when it will
> > be needed to allow children of a common parent to shut down
> > simultaneously.
> >
> > Signed-off-by: Stuart Hayes <stuart.w.hayes@...il.com>
> > Signed-off-by: David Jeffery <djeffery@...hat.com>
> > ---
> >  drivers/base/core.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/base/core.c b/drivers/base/core.c
> > index cbc0099d8ef2..58c772785606 100644
> > --- a/drivers/base/core.c
> > +++ b/drivers/base/core.c
> > @@ -4823,7 +4823,7 @@ void device_shutdown(void)
> >               spin_unlock(&devices_kset->list_lock);
> >
> >               /* hold lock to avoid race with probe/release */
> > -             if (parent)
> > +             if (parent && dev->bus && dev->bus->need_parent_lock)
> >                       device_lock(parent);
>
> What about parents for a device that is not on a bus?  Don't they need
> to be properly locked?

>From my examination of the code and history, I do not believe so.
Locking the parent was added before need_parent_lock was added, and
when the other locations changed to depend on need_parent_lock to lock
both, device_shutdown was left always locking both.

It is simple enough to change the if checks to:

if (parent && (!dev->bus || dev->bus->need_parent_lock))

if you think my understanding is wrong and some bus-less devices have
come to depend on the behavior.

David Jeffery