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Date: Mon, 18 Jan 2021 16:16:16 +0100
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Hans de Goede <hdegoede@...hat.com>
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()
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.
> 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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