On Wed, Jan 09, 2008 at 09:54:56AM -0800, Jay Vosburgh wrote: > Andy Gospodarek <[EMAIL PROTECTED]> wrote: > [...] > >My initial concern was that a slave device could disappear out from > >under us, but it seems like this certainly isn't the case since all > >calls to bond_release are protected by rtnl-locks, so I think you are > >correct that we are safe. I'll test this on my setup here and let you > >know if I see any problems. > > Yep, all entries into enslave or remove come in with RTNL, so if > we have RTNL there then slaves can't vanish. > > On further inspection, I don't think it's safe to simply drop > the locks in bond_set_multicast_list, I'm seeing a couple of cases that > could be troublesome: > > bond_set_promiscuity and bond_set_allmulti both reference > curr_active_slave, which isn't protected from change by RTNL, so that > could conflict with a change_active_slave calling bond_mc_swap (which is > also holding the wrong locks for dev_set_promisc/allmulti). > > It also looks like there are paths (igmp6 for one) into > dev_mc_add that just hold a bunch of regular locks, and not RTNL, so > those wouldn't be safe from having slaves vanish due to concurrent > deslavement.
Eeeek! I didn't realize that rtnl wasn't held for all those calls. If that's the case we can't drop all the locks. > Looks like read_lock_bh for bond-lock and curr_slave_lock is > needed in bond_set_multicast_list, and some dropping of locks is needed > inside bond_set_promisc/allmulti. Methinks that without any locks, > bond_mc_add/delete could race with either a change of active slave or a > de-enslavement of the active slave. Agreed. And despite Herbert's opinion that this isn't the correct fix, I think this will work fine. This is one of the cases where we can take a write_lock(bond->lock) in softirq context, so we need to drop that (or make sure all the read_lock's are read_lock_bh's). The latter isn't really an option since having a majority of the bonding code run in softirq context was what we are trying to avoid with the workqueue conversion. > I'm wondering if this is worth trying to make perfect for 2.6.24 > (and maybe making things worse), and, instead, just do this: > > diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c > index 77d004d..8b9e33a 100644 > --- a/drivers/net/bonding/bond_main.c > +++ b/drivers/net/bonding/bond_main.c > @@ -3937,7 +3937,7 @@ static void bond_set_multicast_list(struct net_device > *bond_dev) > struct bonding *bond = bond_dev->priv; > struct dev_mc_list *dmi; > > - write_lock_bh(&bond->lock); > + read_lock_bh(&bond->lock); > > /* > * Do promisc before checking multicast_mode > @@ -3979,7 +3979,7 @@ static void bond_set_multicast_list(struct net_device > *bond_dev) > bond_mc_list_destroy(bond); > bond_mc_list_copy(bond_dev->mc_list, bond, GFP_ATOMIC); > > - write_unlock_bh(&bond->lock); > + read_unlock_bh(&bond->lock); > } > > /* > > > This should silence the lockdep (if I'm understanding what > everybody's saying), and keep the change set to a minimum. This might The lockdep problem is easy to trigger. The lockdep code does a good job of noticing problems quickly regardless of how easy the deadlocks are to create. > not even be worth pushing for 2.6.24; I'm not exactly sure how difficult > the lockdep problem would be to trigger. > I'd like to see it go in there (for correct-ness) and to avoid hearing about these lockdep issues for the next few months until it makes it into 2.4.25. > The other stuff I mention above can be dealt with later; they're > very low-probability races that would be pretty difficult to hit even on > purpose. > > Thoughts? > > -J > > --- > -Jay Vosburgh, IBM Linux Technology Center, [EMAIL PROTECTED] > -- > To unsubscribe from this list: send the line "unsubscribe netdev" in > the body of a message to [EMAIL PROTECTED] > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
