Re: [PATCH v4 1/4] tty: serdev: Add mutex lock

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Fri, Oct 16, 2026 at 06:00:32PM +0000, Markus Probst wrote:
> Besides more predictable behaviour, this allows for several hardened
> behaviour changes:
> 
> Return -EALREADY in `serdev_device_open` if the device is already open
> instead of causing undefined behaviour.
> 
> Allow calling `serdev_device_close`, even if the device is already
> closed instead of causing a null pointer dereference.
> 
> If the device is left open by the driver after remove, close it and warn
> instead of leaving it in a invalid state.
> 
> Signed-off-by: Markus Probst <markus.probst@posteo.de>
> ---
>  drivers/tty/serdev/core.c           | 10 +++++---
>  drivers/tty/serdev/serdev-ttyport.c | 46 +++++++++++++++++++++++++++++++------
>  include/linux/serdev.h              |  2 +-
>  3 files changed, 47 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/tty/serdev/core.c b/drivers/tty/serdev/core.c
> index 7500efcdfc21..77e8e1d4d2a6 100644
> --- a/drivers/tty/serdev/core.c
> +++ b/drivers/tty/serdev/core.c
> @@ -142,6 +142,11 @@ void serdev_device_remove(struct serdev_device *serdev)
>  	struct serdev_controller *ctrl = serdev->ctrl;
>  
>  	device_unregister(&serdev->dev);
> +
> +	/* Warn if driver did not close the serial device. */
> +	if (ctrl->ops->close && WARN_ON(ctrl->ops->close(ctrl)))

I understand the want to give a big "splat" if this happens, but if it
does somehow, you just crashed the box due to panic-on-warn, which will
result in a CVE being given :)

So, if this ever can happen, we should recover like you do:

> +		pm_runtime_put(&ctrl->dev);

And you can warn about it in the kernel log, but just not with WARN_ON()
please.

thanks,

greg k-h