On Mon, 2012-07-09 at 11:48 +0300, Arik Nemtsov wrote: > On Mon, Jul 9, 2012 at 10:59 AM, Johannes Berg > <johannes@xxxxxxxxxxxxxxxx> wrote: > > On Sun, 2012-07-08 at 19:27 +0300, Arik Nemtsov wrote: > >> On Sat, Jul 7, 2012 at 12:05 AM, Johannes Berg > >> <johannes@xxxxxxxxxxxxxxxx> wrote: > >> > From: Johannes Berg <johannes.berg@xxxxxxxxx> > >> > > >> > Making the scan_sdata pointer usable with RCU makes > >> > it possible to dereference it in the RX path to see > >> > if a received frame actually matches the interface > >> > that is scanning. This is just preparations, making > >> > the pointer __rcu. > >> > >> I noticed no synchronize_rcu() in the start/stop scan calls. Good/bad idea? > > > > Well, start() certainly wouldn't need it since you'd only get NULL :-) > > > > stop() in theory could use it, but it doesn't actually matter because as > > long as the interface still exists the pointer is valid. We don't free > > the interface in scan stop, so we don't need to make sure that the > > pointer is cleared before we continue. And in the case that we *do* in > > fact clear the interface (when it's going down) we have synchronize_rcu > > already in those code paths due to say the interface list with RCU > > protection. > > I meant protecting these (in patch 2/3): > > - local->sched_scanning, > + rcu_dereference_protected(local->sched_scan_sdata, > + lockdep_is_held(&local->mtx)), > > The check is obviously racy here, but it was racy before as well I guess. > I'm not sure why something line test_bit(SCHED_SCANNING) wasn't used > in these places. I don't think I understand what you're trying to say ... why is this racy? We hold the mutex that we always hold when we assign the pointer. johannes -- To unsubscribe from this list: send the line "unsubscribe linux-wireless" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
