Re: [PATCH v2] driver core: complete deferred binds when drivers_autoprobe is off

[Alan Stern <stern@rowland.harvard.edu>]

On Fri, Oct 09, 2026 at 01:22:39PM -0500, mosafer wrote:
> On Fri Oct 9, Danilo Krummrich wrote:
> > We've recently had another patch to fix up cases where dev->driver is
> > pre-assigned. Please see [1] and the corresponding thread.
> >
> > IIRC, there was no reasons the remaining users can't just use a proper
> > match() callback instead, so we don't have to worry about those edge
> > cases in the future.
> 
> Thanks for the pointer.
> 
> I had not seen Kien's series; looking at it now, we are attacking the
> same half-claimed state from opposite ends: his patch makes the release
> path tolerant of it (skip klist_remove() when the device is not bound),
> while mine makes the deferred bind that usb_driver_claim_interface()
> promises actually complete when drivers_autoprobe is off, so the
> half-claimed state never arises.  If the direction is to remove the
> pre-assigned dev->driver users entirely via proper match() callbacks,
> I'm happy for that to supersede this fix -- I'd be glad to help with
> the USB side of that conversion, as I now know the claim/bind/teardown
> paths in detail.
> 
> Until such a conversion lands, though, the window is still open in
> current releases (syzbot hits it, and any userspace writing
> drivers_autoprobe races it), and pre-assignment is not only USB:
> drivers/w1/, drivers/phy/tegra/xusb.c and
> drivers/mailbox/zynqmp-ipi-mailbox.c pre-assign dev->driver the same
> way today.
> 
> So please treat this as: whichever of Kien's guard, this bind-side
> fix, or the match() conversion you want as the canonical answer, this
> patch is yours to drop or pick -- but happy to have your steer before
> it evolves further.

IMO, we do not want the system to limp along forever with the device in 
this "half-bound" state.  Claiming an interface should cause the driver 
core to create a real binding at some point in the near future.

This should happen even without automatic probing.  For example, if both 
interfaces are unbound and the user writes one of them to the driver's 
"bind" sysfs attribute, both interfaces should end up bound to the 
driver after only a short delay.

Alan Stern