linux-kernel - Re: [PATCH v2 2/2] driver core: bus: Correct API bus_rescan

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Message-ID: <2f6d0ffa-89fa-436d-b6f2-f213d9dda8ba@icloud.com>
Date: Wed, 16 Oct 2024 08:16:59 +0800
From: Zijun Hu <zijun_hu@...oud.com>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: linux-kernel@...r.kernel.org, Zijun Hu <quic_zijuhu@...cinc.com>,
 "Rafael J. Wysocki" <rafael@...nel.org>
Subject: Re: [PATCH v2 2/2] driver core: bus: Correct API bus_rescan_devices()
 behavior

On 2024/9/13 07:45, Zijun Hu wrote:
> From: Zijun Hu <quic_zijuhu@...cinc.com>
> 
> API bus_rescan_devices() should ideally scan drivers for a bus's
> devices as many as possible, but it will really stop scanning for
> remaining devices even if a device encounters inconsequential errors
> such as -EPROBE_DEFER, -ENODEV and -EBUSY, fixed by ignoring such
> inconsequential errors and continue to scan drivers for next device.
> 
> By the way, in order to eliminate risk:

The only change for this commit is to make the API scan drivers for more
devices for these inconsequential errors, so it should be low risk.

>  - the API's return value is not changed by recording the first
>    error code during scanning which is returned.
>  - API device_reprobe()'s existing logic is not changed as well.
> 
> Signed-off-by: Zijun Hu <quic_zijuhu@...cinc.com>
> ---
>  drivers/base/bus.c | 38 +++++++++++++++++++++++++-------------
>  1 file changed, 25 insertions(+), 13 deletions(-)
> 
> diff --git a/drivers/base/bus.c b/drivers/base/bus.c
> index 4b5958c5ee7d..fa68acd55bf8 100644
> --- a/drivers/base/bus.c
> +++ b/drivers/base/bus.c
> @@ -58,9 +58,6 @@ static int __must_check bus_rescan_single_device(struct device *dev)
>  	return ret;
>  }
>  
> -static int __must_check bus_rescan_devices_helper(struct device *dev,
> -						void *data);
> -
>  /**
>   * bus_to_subsys - Turn a struct bus_type into a struct subsys_private
>   *
> @@ -797,15 +794,23 @@ static int __must_check bus_rescan_devices_helper(struct device *dev,
>  						  void *data)
>  {
>  	int ret = 0;
> +	int *first_error = data;
>  
> -	if (!dev->driver) {

Also remove this check dev->driver because it is redundant since
__device_attach() also has such check but under device_lock()'s protection.

> -		if (dev->parent && dev->bus->need_parent_lock)
> -			device_lock(dev->parent);
> -		ret = device_attach(dev);
> -		if (dev->parent && dev->bus->need_parent_lock)
> -			device_unlock(dev->parent);
> -	}
> -	return ret < 0 ? ret : 0;
> +	ret = bus_rescan_single_device(dev);
> +
> +	if (ret >= 0)
> +		return 0;
> +
> +	if (!*first_error)
> +		*first_error = ret;
> +	/*
> +	 * Ignore these inconsequential errors and continue to
> +	 * scan drivers for next device.
> +	 */
> +	if (ret == -EPROBE_DEFER || ret == -ENODEV || ret == -EBUSY)
> +		return 0;

which types of error should stop me from scanning drivers for next device ?

is it suitable to ignore all errors here ?

> +
> +	return ret;
>  }
>  
>  /**
> @@ -818,7 +823,10 @@ static int __must_check bus_rescan_devices_helper(struct device *dev,
>   */
>  int bus_rescan_devices(const struct bus_type *bus)
>  {
> -	return bus_for_each_dev(bus, NULL, NULL, bus_rescan_devices_helper);
> +	int err = 0;
> +

in order to keep return value as-is, the first error code is
recorded then returned.

> +	bus_for_each_dev(bus, NULL, &err, bus_rescan_devices_helper);
> +	return err;
>  }
>  EXPORT_SYMBOL_GPL(bus_rescan_devices);
>  
> @@ -833,9 +841,13 @@ EXPORT_SYMBOL_GPL(bus_rescan_devices);
>   */
>  int device_reprobe(struct device *dev)
>  {
> +	int ret;
> +
>  	if (dev->driver)
>  		device_driver_detach(dev);
> -	return bus_rescan_devices_helper(dev, NULL);
> +
> +	ret = bus_rescan_single_device(dev);
> +	return ret < 0 ? ret : 0;
>  }
>  EXPORT_SYMBOL_GPL(device_reprobe);
>  
>