linux-kernel - Re: [PATCH v2 5/5] ACPI: scan: Fix race related to dropping dependencies

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Date:   Wed, 16 Jun 2021 20:04:58 +0200
From:   Hans de Goede <hdegoede@...hat.com>
To:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Linux ACPI <linux-acpi@...r.kernel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 5/5] ACPI: scan: Fix race related to dropping
 dependencies

Hi,

On 6/16/21 8:00 PM, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> 
> If acpi_add_single_object() runs concurrently with respect to
> acpi_scan_clear_dep() which deletes a dependencies list entry where
> the device being added is the consumer, the device's dep_unmet
> counter may not be updated to reflect that change.
> 
> Namely, if the dependencies list entry is deleted right after
> calling acpi_scan_dep_init() and before calling acpi_device_add(),
> acpi_scan_clear_dep() will not find the device object corresponding
> to the consumer device ACPI handle and it will not update its
> dep_unmet counter to reflect the deletion of the list entry.
> Consequently, the dep_unmet counter of the device will never
> become zero going forward which may prevent it from being
> completely enumerated.
> 
> To address this problem, modify acpi_add_single_object() to run
> acpi_tie_acpi_dev(), to attach the ACPI device object created by it
> to the corresponding ACPI namespace node, under acpi_dep_list_lock
> along with acpi_scan_dep_init() whenever the latter is called.
> 
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> Reviewed-by: Hans de Goede <hdegoede@...hat.com>

FWIW this looks good to me now.

Regards,

Hans


> ---
> 
> -> v2:
>    * Fix memory leak spotted by Hans.
>    * Add the R-by tag from Hans.
> 
> ---
>  drivers/acpi/scan.c |   50 ++++++++++++++++++++++++++++++++------------------
>  1 file changed, 32 insertions(+), 18 deletions(-)
> 
> Index: linux-pm/drivers/acpi/scan.c
> ===================================================================
> --- linux-pm.orig/drivers/acpi/scan.c
> +++ linux-pm/drivers/acpi/scan.c
> @@ -657,16 +652,12 @@ static int acpi_tie_acpi_dev(struct acpi
>  	return 0;
>  }
>  
> -int acpi_device_add(struct acpi_device *device,
> -		    void (*release)(struct device *))
> +int __acpi_device_add(struct acpi_device *device,
> +		      void (*release)(struct device *))
>  {
>  	struct acpi_device_bus_id *acpi_device_bus_id;
>  	int result;
>  
> -	result = acpi_tie_acpi_dev(device);
> -	if (result)
> -		return result;
> -
>  	/*
>  	 * Linkage
>  	 * -------
> @@ -755,6 +746,17 @@ err_unlock:
>  	return result;
>  }
>  
> +int acpi_device_add(struct acpi_device *adev, void (*release)(struct device *))
> +{
> +	int ret;
> +
> +	ret = acpi_tie_acpi_dev(adev);
> +	if (ret)
> +		return ret;
> +
> +	return __acpi_device_add(adev, release);
> +}
> +
>  /* --------------------------------------------------------------------------
>                                   Device Enumeration
>     -------------------------------------------------------------------------- */
> @@ -1681,14 +1683,10 @@ static void acpi_scan_dep_init(struct ac
>  {
>  	struct acpi_dep_data *dep;
>  
> -	mutex_lock(&acpi_dep_list_lock);
> -
>  	list_for_each_entry(dep, &acpi_dep_list, node) {
>  		if (dep->consumer == adev->handle)
>  			adev->dep_unmet++;
>  	}
> -
> -	mutex_unlock(&acpi_dep_list_lock);
>  }
>  
>  void acpi_device_add_finalize(struct acpi_device *device)
> @@ -1707,6 +1705,7 @@ static int acpi_add_single_object(struct
>  				  acpi_handle handle, int type, bool dep_init)
>  {
>  	struct acpi_device *device;
> +	bool release_dep_lock = false;
>  	int result;
>  
>  	device = kzalloc(sizeof(struct acpi_device), GFP_KERNEL);
> @@ -1720,16 +1719,31 @@ static int acpi_add_single_object(struct
>  	 * this must be done before the get power-/wakeup_dev-flags calls.
>  	 */
>  	if (type == ACPI_BUS_TYPE_DEVICE || type == ACPI_BUS_TYPE_PROCESSOR) {
> -		if (dep_init)
> +		if (dep_init) {
> +			mutex_lock(&acpi_dep_list_lock);
> +			/*
> +			 * Hold the lock until the acpi_tie_acpi_dev() call
> +			 * below to prevent concurrent acpi_scan_clear_dep()
> +			 * from deleting a dependency list entry without
> +			 * updating dep_unmet for the device.
> +			 */
> +			release_dep_lock = true;
>  			acpi_scan_dep_init(device);
> -
> +		}
>  		acpi_scan_init_status(device);
>  	}
>  
>  	acpi_bus_get_power_flags(device);
>  	acpi_bus_get_wakeup_device_flags(device);
>  
> -	result = acpi_device_add(device, acpi_device_release);
> +	result = acpi_tie_acpi_dev(device);
> +
> +	if (release_dep_lock)
> +		mutex_unlock(&acpi_dep_list_lock);
> +
> +	if (!result)
> +		result = __acpi_device_add(device, acpi_device_release);
> +
>  	if (result) {
>  		acpi_device_release(&device->dev);
>  		return result;
> 
> 
>