Re: [PATCH] Revert "driver core: enforce device_lock for driver_match_device()"

["Danilo Krummrich" <dakr@kernel.org>]

On Mon Mar 2, 2026 at 1:25 AM CET, Danilo Krummrich wrote:
> This reverts commit dc23806a7c47 ("driver core: enforce device_lock for
> driver_match_device()") and commit 289b14592cef ("driver core: fix
> inverted "locked" suffix of driver_match_device()").
>
> While technically correct, there is a major downside to this approach:
>
> When a device is already present in the system and a driver is
> registered on the same bus, we iterate over all devices registered on
> this bus to see if one of them matches. If we come across an already
> bound one where the corresponding driver crashed while holding the
> device lock (e.g. in probe()) we can't make any progress anymore.
>
> However, drivers are typically the least tested code in the kernel and
> hence it is a case that is likely to happen regularly. Besides hurting
> developer ergonomics, it potentially decreases chances of shutting
> things down cleanly and obtaining logs in production environments as
> well. [1]
>
> This came up in the context of a firewire bug, which only in combination
> with the reverted commit, caused the machine to hang. [2]
>
> Thus, revert commit dc23806a7c47 ("driver core: enforce device_lock for
> driver_match_device()") and add a brief note clarifying that an
> implementer of struct bus_type must not expect match() to be called with
> the device lock held.
>
> Link: https://lore.kernel.org/driver-core/DGRGTIRHA62X.3RY09D9SOK77P@kernel.org/ [1]
> Link: https://lore.kernel.org/all/67f655bb-4d81-4609-b008-68d200255dd2@davidgow.net/ [2]
> Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
> Closes: https://lore.kernel.org/driver-core/CAHk-=wgJ_L1C=HjcYJotg_zrZEmiLFJaoic+PWthjuQrutrfJw@mail.gmail.com/
> Signed-off-by: Danilo Krummrich <dakr@kernel.org>

Follow-up regarding driver_override: https://lore.kernel.org/driver-core/20260302002729.19438-1-dakr@kernel.org/