Re: [PATCH v3 1/3] Revert "drivers: core: synchronize really_probe() and dev_uevent()"

[Aditya Garg <gargaditya08@live.com>]

> On 11 Mar 2025, at 10:54 AM, Dmitry Torokhov <dmitry.torokhov@gmail.com> wrote:
> 
> This reverts commit c0a40097f0bc81deafc15f9195d1fb54595cd6d0.
> 
> Probing a device can take arbitrary long time. In the field we observed
> that, for example, probing a bad micro-SD cards in an external USB card
> reader (or maybe cards were good but cables were flaky) sometimes takes
> longer than 2 minutes due to multiple retries at various levels of the
> stack. We can not block uevent_show() method for that long because udev
> is reading that attribute very often and that blocks udev and interferes
> with booting of the system.
> 
> The change that introduced locking was concerned with dev_uevent()
> racing with unbinding the driver. However we can handle it without
> locking (which will be done in subsequent patch).
> 
> There was also claim that synchronization with probe() is needed to
> properly load USB drivers, however this is a red herring: the change
> adding the lock was introduced in May of last year and USB loading and
> probing worked properly for many years before that.
> 
> Revert the harmful locking.
> 
> Cc: stable@vger.kernel.org
> Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
> ---

Hi

For sometime users of the appletbdrm driver used for Touch Bar support on T2 Macs (https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/gpu/drm/tiny/appletbdrm.c?h=v7.0-rc4) have been facing a regression that caused the Touch Bar to no longer work on resume. A person tried to bisect and this commit was found to be the reason.

The person has tried to explain the whole situation in this GitHub issue: https://github.com/t2linux/wiki/issues/635#issuecomment-4092907335

And this seems to be the most plausible explanation: https://github.com/t2linux/wiki/issues/635#issuecomment-4071720148

Thanks
Aditya