linux-kernel - Re: [PATCH 1/3] driver core: bus: introduce can

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Date: Mon, 5 Feb 2024 09:48:39 +0100
From: Christian König <ckoenig.leichtzumerken@...il.com>
To: Hamza Mahfooz <hamza.mahfooz@....com>, linux-kernel@...r.kernel.org
Cc: stable@...r.kernel.org, Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 "Rafael J. Wysocki" <rafael@...nel.org>,
 Alex Deucher <alexander.deucher@....com>,
 Christian König <christian.koenig@....com>,
 "Pan, Xinhui" <Xinhui.Pan@....com>, David Airlie <airlied@...il.com>,
 Daniel Vetter <daniel@...ll.ch>, Bjorn Helgaas <bhelgaas@...gle.com>,
 Mario Limonciello <mario.limonciello@....com>,
 Lijo Lazar <lijo.lazar@....com>,
 Srinivasan Shanmugam <srinivasan.shanmugam@....com>, Le Ma <le.ma@....com>,
 André Almeida <andrealmeid@...lia.com>,
 James Zhu <James.Zhu@....com>, Aurabindo Pillai <aurabindo.pillai@....com>,
 Joerg Roedel <jroedel@...e.de>, Iwona Winiarska <iwona.winiarska@...el.com>,
 Robin Murphy <robin.murphy@....com>, amd-gfx@...ts.freedesktop.org,
 dri-devel@...ts.freedesktop.org, linux-pci@...r.kernel.org
Subject: Re: [PATCH 1/3] driver core: bus: introduce can_remove()

Am 02.02.24 um 23:25 schrieb Hamza Mahfooz:
> Currently, drivers have no mechanism to block requests to unbind
> devices. However, this can cause resource leaks and leave the device in
> an inconsistent state, such that rebinding the device may cause a hang
> or otherwise prevent the device from being rebound. So, introduce
> the can_remove() callback to allow drivers to indicate if it isn't
> appropriate to remove a device at the given time.

Well that is nonsense. When you physically remove a device (e.g. unplug 
it) then there is nothing in software you can do to prevent that.

Regards,
Christian.

>
> Cc: stable@...r.kernel.org
> Signed-off-by: Hamza Mahfooz <hamza.mahfooz@....com>
> ---
>   drivers/base/bus.c         | 4 ++++
>   include/linux/device/bus.h | 2 ++
>   2 files changed, 6 insertions(+)
>
> diff --git a/drivers/base/bus.c b/drivers/base/bus.c
> index daee55c9b2d9..7c259b01ea99 100644
> --- a/drivers/base/bus.c
> +++ b/drivers/base/bus.c
> @@ -239,6 +239,10 @@ static ssize_t unbind_store(struct device_driver *drv, const char *buf,
>   
>   	dev = bus_find_device_by_name(bus, NULL, buf);
>   	if (dev && dev->driver == drv) {
> +		if (dev->bus && dev->bus->can_remove &&
> +		    !dev->bus->can_remove(dev))
> +			return -EBUSY;
> +
>   		device_driver_detach(dev);
>   		err = count;
>   	}
> diff --git a/include/linux/device/bus.h b/include/linux/device/bus.h
> index 5ef4ec1c36c3..c9d4af0ed3b8 100644
> --- a/include/linux/device/bus.h
> +++ b/include/linux/device/bus.h
> @@ -46,6 +46,7 @@ struct fwnode_handle;
>    *		be called at late_initcall_sync level. If the device has
>    *		consumers that are never bound to a driver, this function
>    *		will never get called until they do.
> + * @can_remove: Called before attempting to remove a device from this bus.
>    * @remove:	Called when a device removed from this bus.
>    * @shutdown:	Called at shut-down time to quiesce the device.
>    *
> @@ -85,6 +86,7 @@ struct bus_type {
>   	int (*uevent)(const struct device *dev, struct kobj_uevent_env *env);
>   	int (*probe)(struct device *dev);
>   	void (*sync_state)(struct device *dev);
> +	bool (*can_remove)(struct device *dev);
>   	void (*remove)(struct device *dev);
>   	void (*shutdown)(struct device *dev);
>