From: Johan Hovold <johan@kernel.org>
To: Danilo Krummrich <dakr@kernel.org>
Cc: Mario Peter <mario.peter@leica-geosystems.com>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
"Rafael J. Wysocki" <rafael@kernel.org>,
Dmitry Torokhov <dmitry.torokhov@gmail.com>,
Alan Stern <stern@rowland.harvard.edu>,
driver-core@lists.linux.dev, linux-usb@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] driver core: Take parent lock in async device attach
Date: Mon, 12 Oct 2026 17:12:41 +0200 [thread overview]
Message-ID: <asz46b5IgxH8vfBY@hovoldconsulting.com> (raw)
In-Reply-To: <DM2X6XX7EGLN.38C96USJFEV4Y@kernel.org>
On Mon, Oct 12, 2026 at 04:13:16PM +0200, Danilo Krummrich wrote:
> On Mon Oct 12, 2026 at 2:50 PM CEST, Johan Hovold wrote:
> > On Wed, Oct 07, 2026 at 01:15:14PM +0000, Mario Peter wrote:
> >> Take the parent lock in __device_attach_async_helper() as well, like
> >> __driver_attach_async_helper() does, and move
> >> __device_driver_lock/unlock() up for that. With this the warning was
> >> gone in 300 boots on the board and in 6000 iterations in QEMU.
> > Thanks for fixing this, USB interfaces should indeed always be probed
> > with the parent lock held:
>
> I was about to pick this up, but can't this cause a subtle deadlock? What if
> async_schedule_dev() runs synchronously? Wouldn't we then attempt to take the
> parent lock again while e.g. bConfigurationValue_store() already holds it?
Hmm. Good catch. I guess we need to switch to
async_schedule_dev_nocall() and retry with explicit synchronous probe on
errors.
Johan
prev parent reply other threads:[~2026-10-12 15:12 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-10-07 13:15 [PATCH v2] driver core: Take parent lock in async device attach Mario Peter
2026-10-12 12:50 ` Johan Hovold
2026-10-12 14:13 ` Danilo Krummrich
2026-10-12 15:12 ` Johan Hovold [this message]
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