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. -- 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
