On 04/11/2013 02:19 AM, Johannes Berg wrote:
On Tue, 2013-04-09 at 10:54 -0700, Ben Greear wrote:
+struct sta_info *sta_info_get_by_vif(struct ieee80211_local *local,
+ const u8 *vif_addr, const u8 * sta_addr) {
+ struct sta_info *sta;
+
+ sta = rcu_dereference_check(local->sta_vhash[STA_HASH(vif_addr)],
+ lockdep_is_held(&local->sta_mtx));
+ while (sta) {
+ if (ether_addr_equal(sta->sdata->vif.addr, vif_addr) &&
+ ether_addr_equal(sta->sta.addr, sta_addr))
+ break;
+ sta = rcu_dereference_check(sta->vnext,
+ lockdep_is_held(&local->sta_mtx));
Almost all of your rcu_dereference_check() invocations should be
rcu_dereference_protected(). See include/linux/rcupdate.h :)
Now this, I'm not so sure of. That rcu_dereference_protected seems to
be only used for the 'update-side' use. I was under the impression
that when the mac80211 rx logic is called we are only protected by rcu,
not the update mutex.
Ah, yes, I was reading this the wrong way, sorry. Here the _check() is
correct of course -- you want to be either under RCU protection or hold
the sta_mtx.
I also struggle to understand RCU properly...so maybe I'm just
wrong about all that...
The other methods to get sta_info around that code use the _check() variant,
by the way...
Yeah ... :)
Another question: Have you thought about hashing the virtual interfaces
instead of the stations, and then hashing the stations inside each
virtual interface? That would make it a bit of a two-level thing:
A1 (in the frame) -> virtual interface
A2 (frame) -> station
But it would address the TX side efficiently without "some_sta" since
you know the virtual interface there already, and could potentially have
less impact on the code? On TX it'd actually even be more efficient if
you have more than 1 station per interface (right now you don't though)
This idea suddenly looks a lot more interesting. The ieee80211_tx_status method needs
to find the remote station & sdata, but in the AP case, the station hash works best,
and in my many-sta-vif case, the VIF hash works best. I don't see any way to guess
which hash to use in this case.
But, if we first hashed to find sdata, and then had a vif hash in the sdata
object, the lookup should be fast for cases where the hash function works
well.
I'll give this a try...
Thanks,
Ben
--
Ben Greear <greearb@xxxxxxxxxxxxxxx>
Candela Technologies Inc http://www.candelatech.com
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