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Date: Mon, 18 Jan 2021 16:26:05 +0100
From: Hans de Goede <hdegoede@...hat.com>
To: "Rafael J. Wysocki" <rafael@...nel.org>
Cc: "Rafael J. Wysocki" <rjw@...ysocki.net>,
Linux ACPI <linux-acpi@...r.kernel.org>,
LKML <linux-kernel@...r.kernel.org>,
Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Subject: Re: [PATCH v1 1/2] ACPI: scan: Rearrange memory allocation in
acpi_device_add()
Hi,
On 1/18/21 4:16 PM, Rafael J. Wysocki wrote:
> On Sat, Jan 16, 2021 at 1:37 PM Hans de Goede <hdegoede@...hat.com> wrote:
>>
>> Hi,
>>
>> On 1/14/21 7:46 PM, Rafael J. Wysocki wrote:
>>> From: Rafael J. Wysocki <rafael.j.wysocki@...el.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@...el.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.
>
> Yes, that looks better.
>
> Let me do it this way, but I won't resend the patch if you don't mind.
Not resending is fine.
Regards,
Hans
>
>> Either way, with or without this change, the patch looks good to me:
>>
>> Reviewed-by: Hans de Goede <hdegoede@...hat.com>
>
> Thanks!
>
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