On Wed, Jun 16, 2021 at 4:48 PM Hans de Goede <hdegoede@xxxxxxxxxx> wrote:
>
> Hi,
>
> On 6/16/21 4:23 PM, Rafael J. Wysocki wrote:
> > From: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
> >
> > In general, acpi_bus_attach() can only be run safely under
> > acpi_scan_lock, but that lock cannot be acquired under
> > acpi_dep_list_lock, so make acpi_scan_clear_dep() schedule deferred
> > execution of acpi_bus_attach() under acpi_scan_lock instead of
> > calling it directly.
> >
> > This also fixes a possible race between acpi_scan_clear_dep() and
> > device removal that might cause a device object that went away to
> > be accessed, because acpi_scan_clear_dep() is changed to acquire
> > a reference on the consumer device object.
> >
> > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
> > ---
> > drivers/acpi/scan.c | 50 +++++++++++++++++++++++++++++++++++++++++++++-----
> > 1 file changed, 45 insertions(+), 5 deletions(-)
> >
> > Index: linux-pm/drivers/acpi/scan.c
> > ===================================================================
> > --- linux-pm.orig/drivers/acpi/scan.c
> > +++ linux-pm/drivers/acpi/scan.c
> > @@ -2115,16 +2115,56 @@ static int acpi_dev_get_first_consumer_d
> > return 0;
> > }
> >
> > -static int acpi_scan_clear_dep(struct acpi_dep_data *dep, void *data)
> > -{
> > +struct acpi_scan_clear_dep_work {
> > + struct work_struct work;
> > struct acpi_device *adev;
> > +};
> > +
> > +static void acpi_scan_clear_dep_fn(struct work_struct *work)
> > +{
> > + struct acpi_scan_clear_dep_work *cdw;
> > +
> > + cdw = container_of(work, struct acpi_scan_clear_dep_work, work);
> >
> > - acpi_bus_get_device(dep->consumer, &adev);
> > + acpi_scan_lock_acquire();
> > + acpi_bus_attach(cdw->adev, true);
> > + acpi_scan_lock_release();
> > +
> > + acpi_dev_put(cdw->adev);
> > + kfree(cdw);
> > +}
> > +
> > +static bool acpi_scan_clear_dep_queue(struct acpi_device *adev)
> > +{
> > + struct acpi_scan_clear_dep_work *cdw;
> > +
> > + if (adev->dep_unmet)
> > + return false;
> > +
> > + cdw = kmalloc(sizeof(*cdw), GFP_KERNEL);
> > + if (!cdw)
> > + return false;
> > +
> > + cdw->adev = adev;
> > + INIT_WORK(&cdw->work, acpi_scan_clear_dep_fn);
> > + /*
> > + * Since the work function may block on the lock until the entire
> > + * initial enumeration of devices is complete, put it into the unbound
> > + * workqueue.
> > + */
> > + queue_work(system_unbound_wq, &cdw->work);
>
> Hmm, I'm a bit worried about this. Even with the system_unbound_wq
> some code may expect at least some progress being made with processing
> works during the initial enumeration. OTOH this does run pretty early on.
>
> Still I wonder if it would not be better to create + use our own workqueue
> for this ?
>
> I guess we can always do this if we run into issues later...
Exactly my thought.
> With that said / otherwise the patch looks good to me:
>
> Reviewed-by: Hans de Goede <hdegoede@xxxxxxxxxx>
Thanks!
