On Wed, Apr 18, 2018 at 05:14:36PM -0700, Florian Fainelli wrote:
> On 04/18/2018 05:00 PM, Andrew Lunn wrote:
> > mdiobus_register will search for any mdiobus board info registered for
> > the bus being registered. If found, it will probe devices on the bus.
> > That device, if for example it is an ethernet switch, may then try to
> > register an mdio bus. Thus we need to allow recursive calls to
> > mdiobus_register.
> >
> > Holding the mdio_board_lock will cause a deadlock during this
> > recursion. Release the lock and use list_for_each_entry_safe.
> >
> > Signed-off-by: Andrew Lunn <and...@lunn.ch>
> > ---
> > drivers/net/phy/mdio-boardinfo.c | 5 ++++-
> > 1 file changed, 4 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/net/phy/mdio-boardinfo.c
> > b/drivers/net/phy/mdio-boardinfo.c
> > index 1861f387820d..863496fa5d13 100644
> > --- a/drivers/net/phy/mdio-boardinfo.c
> > +++ b/drivers/net/phy/mdio-boardinfo.c
> > @@ -30,17 +30,20 @@ void mdiobus_setup_mdiodev_from_board_info(struct
> > mii_bus *bus,
> > struct mdio_board_info *bi))
> > {
> > struct mdio_board_entry *be;
> > + struct mdio_board_entry *tmp;
> > struct mdio_board_info *bi;
> > int ret;
> >
> > mutex_lock(&mdio_board_lock);
>
> Don't you need to drop that lock here?
>
> > - list_for_each_entry(be, &mdio_board_list, list) {
> > + list_for_each_entry_safe(be, tmp, &mdio_board_list, list) {
> > bi = &be->board_info;
> >
> > if (strcmp(bus->id, bi->bus_id))
> > continue;
> >
> > + mutex_unlock(&mdio_board_lock);
> > ret = cb(bus, bi);
> > + mutex_lock(&mdio_board_lock);
> > if (ret)
> > continue;
> >
>
> And conversely drop the unlock from the end of this function?
No. The recursion happens inside the ret = cb(bus, bi). We need the
lock to be available during that. The lock itself is protecting the
list, so we need to hold the lock while using the list.
> Also, would you rather target "net" for this change since this appears
> to be a bug fix?
As far as i know, there is no in tree driver which can trigger
this. It requires the use of a switch instantiated using mdio_board
info, and the switch then needs to add another mdio bus in its probe
function. The only in tree code doing anything like this is dsa_loop,
and it does not register an mdio bus.
However, later this cycle i plan to add support for Zodiac's SCU3, and
it does trigger this deadlock. So net-next is sufficient for my.
Andrew
