Re: [PATCH 2/3] ACPI: Get acpi_device's parent from the parent field

Rafael J. Wysocki
2021-11-03T17:48:44Z

On Wed, Nov 3, 2021 at 6:02 PM Andy Shevchenko
<andriy.shevchenko@intel.com> wrote:
>
> On Wed, Nov 03, 2021 at 03:34:05PM +0200, Sakari Ailus wrote:
> > Printk modifier %pfw is used to print the full path of the device name.
> > This is obtained device by device until a device no longer has a parent.
> >
> > On ACPI getting the parent fwnode is done by calling acpi_get_parent()
> > which tries to down() a semaphore. But local IRQs are now disabled in
> > vprintk_store() before the mutex is acquired. This is obviously a problem.
> >
> > Luckily struct acpi_device has a parent field already.

Which I'm going to eliminate, because it is redundant.

The dev object embedded in struct acpi_device has a parent field
pointing to the same object and that one is used by the driver core.

> > Use that field to get the parent instead of relying on acpi_get_parent().
>
> I think the best if Rafael can confirm that we may use it like this.
> If he approved, nothing would stop me to give you
> Reviewed-by: Andy Shevchenko <andriy.shevchenko@intel.com>

In fact, I would prefer the parent field of the dev object embedded in
struct acpi_device to be used and for completeness it should be tested
against NULL unless you know that the parent is not going away ATM.

> > Fixes: 002eb6ad0751 ("printk: track/limit recursion")
> > Cc: stable@vger.kernel.org # v5.15 and up
> > Depends-on: ("ACPI: Make acpi_fwnode_handle safer")
> > Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
> > ---
> > drivers/acpi/property.c | 12 ++++--------
> > 1 file changed, 4 insertions(+), 8 deletions(-)
> >
> > diff --git a/drivers/acpi/property.c b/drivers/acpi/property.c
> > index e312ebaed8db4..7403ee2816eb8 100644
> > --- a/drivers/acpi/property.c
> > +++ b/drivers/acpi/property.c
> > @@ -1089,16 +1089,12 @@ struct fwnode_handle *acpi_node_get_parent(const struct fwnode_handle *fwnode)
> > if (is_acpi_data_node(fwnode)) {
> > /* All data nodes have parent pointer so just return that */
> > return to_acpi_data_node(fwnode)->parent;
> > - } else if (is_acpi_device_node(fwnode)) {
> > - acpi_handle handle, parent_handle;
> > + }
> >
> > - handle = to_acpi_device_node(fwnode)->handle;
> > - if (ACPI_SUCCESS(acpi_get_parent(handle, &parent_handle))) {
> > - struct acpi_device *adev;
> > + if (is_acpi_device_node(fwnode)) {
> > + struct acpi_device *device = to_acpi_device_node(fwnode);

Call this variable adev please.

> >
> > - if (!acpi_bus_get_device(parent_handle, &adev))
> > - return acpi_fwnode_handle(adev);
> > - }
> > + return acpi_fwnode_handle(device->parent);

And then

adev = to_acpi_device(&device->dev.parent);
if (adev)
return acpi_fwnode_handle(adev);

> > }
> >
> > return NULL;
> > --
> > 2.30.2
> >
> >
>
> --
> With Best Regards,
> Andy Shevchenko
>
>