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SubjectRe: [PATCH v1 1/2] ACPI: scan: Rearrange memory allocation in acpi_device_add()
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Hi,

On 1/14/21 7:46 PM, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
>
> The upfront allocation of new_bus_id is done to avoid allocating
> memory under acpi_device_lock, but it doesn't really help,
> because (1) it leads to many unnecessary memory allocations for
> _ADR devices, (2) kstrdup_const() is run under that lock anyway and
> (3) it complicates the code.
>
> Rearrange acpi_device_add() to allocate memory for a new struct
> acpi_device_bus_id instance only when necessary, eliminate a redundant
> local variable from it and reduce the number of labels in there.
>
> No intentional functional impact.
>
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> ---
> drivers/acpi/scan.c | 57 +++++++++++++++++++++++-----------------------------
> 1 file changed, 26 insertions(+), 31 deletions(-)
>
> Index: linux-pm/drivers/acpi/scan.c
> ===================================================================
> --- linux-pm.orig/drivers/acpi/scan.c
> +++ linux-pm/drivers/acpi/scan.c
> @@ -621,12 +621,23 @@ void acpi_bus_put_acpi_device(struct acp
> put_device(&adev->dev);
> }
>
> +static struct acpi_device_bus_id *acpi_device_bus_id_match(const char *dev_id)
> +{
> + struct acpi_device_bus_id *acpi_device_bus_id;
> +
> + /* Find suitable bus_id and instance number in acpi_bus_id_list. */
> + list_for_each_entry(acpi_device_bus_id, &acpi_bus_id_list, node) {
> + if (!strcmp(acpi_device_bus_id->bus_id, dev_id))
> + return acpi_device_bus_id;
> + }
> + return NULL;
> +}
> +
> int acpi_device_add(struct acpi_device *device,
> void (*release)(struct device *))
> {
> + struct acpi_device_bus_id *acpi_device_bus_id;
> int result;
> - struct acpi_device_bus_id *acpi_device_bus_id, *new_bus_id;
> - int found = 0;
>
> if (device->handle) {
> acpi_status status;
> @@ -652,38 +663,26 @@ int acpi_device_add(struct acpi_device *
> INIT_LIST_HEAD(&device->del_list);
> mutex_init(&device->physical_node_lock);
>
> - new_bus_id = kzalloc(sizeof(struct acpi_device_bus_id), GFP_KERNEL);
> - if (!new_bus_id) {
> - pr_err(PREFIX "Memory allocation error\n");
> - result = -ENOMEM;
> - goto err_detach;
> - }
> -
> mutex_lock(&acpi_device_lock);
> - /*
> - * Find suitable bus_id and instance number in acpi_bus_id_list
> - * If failed, create one and link it into acpi_bus_id_list
> - */
> - list_for_each_entry(acpi_device_bus_id, &acpi_bus_id_list, node) {
> - if (!strcmp(acpi_device_bus_id->bus_id,
> - acpi_device_hid(device))) {
> - acpi_device_bus_id->instance_no++;
> - found = 1;
> - kfree(new_bus_id);
> - break;
> +
> + acpi_device_bus_id = acpi_device_bus_id_match(acpi_device_hid(device));
> + if (acpi_device_bus_id) {
> + acpi_device_bus_id->instance_no++;
> + } else {
> + acpi_device_bus_id = kzalloc(sizeof(*acpi_device_bus_id),
> + GFP_KERNEL);
> + if (!acpi_device_bus_id) {
> + result = -ENOMEM;
> + goto err_unlock;
> }
> - }
> - if (!found) {
> - acpi_device_bus_id = new_bus_id;
> acpi_device_bus_id->bus_id =
> kstrdup_const(acpi_device_hid(device), GFP_KERNEL);
> if (!acpi_device_bus_id->bus_id) {
> - pr_err(PREFIX "Memory allocation error for bus id\n");
> + kfree(acpi_device_bus_id);
> result = -ENOMEM;
> - goto err_free_new_bus_id;
> + goto err_unlock;
> }

When I have cases like this, where 2 mallocs are necessary I typically do it like this:

const char *bus_id;

...

} else {
acpi_device_bus_id = kzalloc(sizeof(*acpi_device_bus_id),
GFP_KERNEL);
bus_id = kstrdup_const(acpi_device_hid(device), GFP_KERNEL);
if (!acpi_device_bus_id || !bus_id) {
kfree(acpi_device_bus_id);
kfree(bus_id);
result = -ENOMEM;
goto err_unlock;
}
acpi_device_bus_id->bus_id = bus_id;
list_add_tail(&acpi_device_bus_id->node, &acpi_bus_id_list);
}

...

So that there is only one if / 1 error-handling path for both mallocs.
I personally find this a bit cleaner.

Either way, with or without this change, the patch looks good to me:

Reviewed-by: Hans de Goede <hdegoede@redhat.com>

Regards,

Hans


>
> - acpi_device_bus_id->instance_no = 0;
> list_add_tail(&acpi_device_bus_id->node, &acpi_bus_id_list);
> }
> dev_set_name(&device->dev, "%s:%02x", acpi_device_bus_id->bus_id, acpi_device_bus_id->instance_no);
> @@ -718,13 +717,9 @@ int acpi_device_add(struct acpi_device *
> list_del(&device->node);
> list_del(&device->wakeup_list);
>
> - err_free_new_bus_id:
> - if (!found)
> - kfree(new_bus_id);
> -
> + err_unlock:
> mutex_unlock(&acpi_device_lock);
>
> - err_detach:
> acpi_detach_data(device->handle, acpi_scan_drop_device);
> return result;
> }
>
>
>

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