On Mon, Jan 18, 2021 at 11:03 PM Saravana Kannan <sarava...@google.com> wrote:
>
> On Fri, Jan 15, 2021 at 10:30 AM Rafael J. Wysocki <r...@rjwysocki.net> wrote:
> >
> > From: Rafael J. Wysocki <rafael.j.wyso...@intel.com>
> >
> > If the device passed as the target (second argument) to
> > device_is_dependent() is not completely registered (that is, it has
> > been initialized, but not added yet), but the parent pointer of it
> > is set, it may be missing from the list of the parent's children
> > and device_for_each_child() called by device_is_dependent() cannot
> > be relied on to catch that dependency.
> >
> > For this reason, modify device_is_dependent() to check the ancestors
> > of the target device by following its parent pointer in addition to
> > the device_for_each_child() walk.
> >
> > Fixes: 9ed9895370ae ("driver core: Functional dependencies tracking
> > support")
> > Signed-off-by: Rafael J. Wysocki <rafael.j.wyso...@intel.com>
> > Reported-by: Stephan Gerhold <step...@gerhold.net>
> > Tested-by: Stephan Gerhold <step...@gerhold.net>
> > ---
> >
> > -> v2:
> > * Improve the changelog.
> > * Add a comment to explain the reason for the extra check.
> > * Add tags.
> >
> > No code changes.
> >
> > ---
> > drivers/base/core.c | 17 ++++++++++++++++-
> > 1 file changed, 16 insertions(+), 1 deletion(-)
> >
> > Index: linux-pm/drivers/base/core.c
> > ===================================================================
> > --- linux-pm.orig/drivers/base/core.c
> > +++ linux-pm/drivers/base/core.c
> > @@ -208,6 +208,16 @@ int device_links_read_lock_held(void)
> > #endif
> > #endif /* !CONFIG_SRCU */
> >
> > +static bool device_is_ancestor(struct device *dev, struct device *target)
> > +{
> > + while (target->parent) {
> > + target = target->parent;
> > + if (dev == target)
> > + return true;
> > + }
> > + return false;
> > +}
> > +
> > /**
> > * device_is_dependent - Check if one device depends on another one
> > * @dev: Device to check dependencies for.
> > @@ -221,7 +231,12 @@ int device_is_dependent(struct device *d
> > struct device_link *link;
> > int ret;
> >
> > - if (dev == target)
> > + /*
> > + * The "ancestors" check is needed to catch the case when the target
> > + * device has not been completely initialized yet and it is still
> > + * missing from the list of children of its parent device.
> > + */
> > + if (dev == target || device_is_ancestor(dev, target))
> > return 1;
> >
> > ret = device_for_each_child(dev, target, device_is_dependent);
> >
>
> Reviewed-by: Saravana Kannan <sarava...@google.com>
>
> fw_devlink_relax_cycle() needs a similar fix. Want me to handle that
> as a separate patch to driver-core-next? Or do you want to combine
> that in this patch?
I would prefer that to be a different patch because of the Fixes: tag.
Also fw_devlink_relax_cycle() is in linux-next only for now, so it is
better to avoid mixing a mainline fix with updating that one.
