[PATCH] mac80211: protect AP VLAN list with local->mtx

[PATCH] mac80211: protect AP VLAN list with local->mtx

[Michal Kazior]

It was impossible to change chanctx of master AP
for AP VLANs because the copy function requires
RTNL which can't be simply taken in mac80211 code
due to possible deadlocks.

This is required for future chanctx reservation
that re-bind vifs to new chanctx. This requires
safe AP VLAN iteration without RTNL.

Now VLANs can be iterated while holding either
RTNL or local->mtx because the list is modified
while holding both of these locks.

Signed-off-by: Michal Kazior <michal.kazior@tieto.com>
---
 net/mac80211/cfg.c         | 5 +++--
 net/mac80211/chan.c        | 2 +-
 net/mac80211/ieee80211_i.h | 4 ++--
 net/mac80211/iface.c       | 9 ++++++++-
 4 files changed, 14 insertions(+), 6 deletions(-)

diff --git a/net/mac80211/cfg.c b/net/mac80211/cfg.c
index aaa59d7..adf66a5 100644
--- a/net/mac80211/cfg.c
+++ b/net/mac80211/cfg.c
@@ -975,10 +975,11 @@ static int ieee80211_start_ap(struct wiphy *wiphy, struct net_device *dev,
 	sdata->radar_required = params->radar_required;
 	err = ieee80211_vif_use_channel(sdata, &params->chandef,
 					IEEE80211_CHANCTX_SHARED);
+	if (!err)
+		ieee80211_vif_copy_chanctx_to_vlans(sdata, false);
 	mutex_unlock(&local->mtx);
 	if (err)
 		return err;
-	ieee80211_vif_copy_chanctx_to_vlans(sdata, false);
 
 	/*
 	 * Apply control port protocol, this allows us to
@@ -1131,8 +1132,8 @@ static int ieee80211_stop_ap(struct wiphy *wiphy, struct net_device *dev)
 	local->total_ps_buffered -= skb_queue_len(&sdata->u.ap.ps.bc_buf);
 	skb_queue_purge(&sdata->u.ap.ps.bc_buf);
 
-	ieee80211_vif_copy_chanctx_to_vlans(sdata, true);
 	mutex_lock(&local->mtx);
+	ieee80211_vif_copy_chanctx_to_vlans(sdata, true);
 	ieee80211_vif_release_channel(sdata);
 	mutex_unlock(&local->mtx);
 
diff --git a/net/mac80211/chan.c b/net/mac80211/chan.c
index 42c6592..fdbb932 100644
--- a/net/mac80211/chan.c
+++ b/net/mac80211/chan.c
@@ -689,7 +689,7 @@ void ieee80211_vif_copy_chanctx_to_vlans(struct ieee80211_sub_if_data *sdata,
 	struct ieee80211_sub_if_data *vlan;
 	struct ieee80211_chanctx_conf *conf;
 
-	ASSERT_RTNL();
+	lockdep_assert_held(&local->mtx);
 
 	if (WARN_ON(sdata->vif.type != NL80211_IFTYPE_AP))
 		return;
diff --git a/net/mac80211/ieee80211_i.h b/net/mac80211/ieee80211_i.h
index 8603dfb..2f662ca 100644
--- a/net/mac80211/ieee80211_i.h
+++ b/net/mac80211/ieee80211_i.h
@@ -260,7 +260,7 @@ struct ieee80211_if_ap {
 
 	/* to be used after channel switch. */
 	struct cfg80211_beacon_data *next_beacon;
-	struct list_head vlans;
+	struct list_head vlans; /* write-protected with RTNL and local->mtx */
 
 	struct ps_data ps;
 	atomic_t num_mcast_sta; /* number of stations receiving multicast */
@@ -276,7 +276,7 @@ struct ieee80211_if_wds {
 };
 
 struct ieee80211_if_vlan {
-	struct list_head list;
+	struct list_head list; /* write-protected with RTNL and local->mtx */
 
 	/* used for all tx if the VLAN is configured to 4-addr mode */
 	struct sta_info __rcu *sta;
diff --git a/net/mac80211/iface.c b/net/mac80211/iface.c
index be198f4..c34095b 100644
--- a/net/mac80211/iface.c
+++ b/net/mac80211/iface.c
@@ -492,7 +492,9 @@ int ieee80211_do_open(struct wireless_dev *wdev, bool coming_up)
 		if (!sdata->bss)
 			return -ENOLINK;
 
+		mutex_lock(&local->mtx);
 		list_add(&sdata->u.vlan.list, &sdata->bss->vlans);
+		mutex_unlock(&local->mtx);
 
 		master = container_of(sdata->bss,
 				      struct ieee80211_sub_if_data, u.ap);
@@ -722,8 +724,11 @@ int ieee80211_do_open(struct wireless_dev *wdev, bool coming_up)
 		drv_stop(local);
  err_del_bss:
 	sdata->bss = NULL;
-	if (sdata->vif.type == NL80211_IFTYPE_AP_VLAN)
+	if (sdata->vif.type == NL80211_IFTYPE_AP_VLAN) {
+		mutex_lock(&local->mtx);
 		list_del(&sdata->u.vlan.list);
+		mutex_unlock(&local->mtx);
+	}
 	/* might already be clear but that doesn't matter */
 	clear_bit(SDATA_STATE_RUNNING, &sdata->state);
 	return res;
@@ -875,7 +880,9 @@ static void ieee80211_do_stop(struct ieee80211_sub_if_data *sdata,
 
 	switch (sdata->vif.type) {
 	case NL80211_IFTYPE_AP_VLAN:
+		mutex_lock(&local->mtx);
 		list_del(&sdata->u.vlan.list);
+		mutex_unlock(&local->mtx);
 		rcu_assign_pointer(sdata->vif.chanctx_conf, NULL);
 		/* no need to tell driver */
 		break;
-- 
1.8.5.3

Re: [PATCH] mac80211: protect AP VLAN list with local->mtx

[Luca Coelho]

On Wed, 2014-03-05 at 13:14 +0100, Michal Kazior wrote:
> It was impossible to change chanctx of master AP
> for AP VLANs because the copy function requires
> RTNL which can't be simply taken in mac80211 code
> due to possible deadlocks.
> 
> This is required for future chanctx reservation
> that re-bind vifs to new chanctx. This requires
> safe AP VLAN iteration without RTNL.
> 
> Now VLANs can be iterated while holding either
> RTNL or local->mtx because the list is modified
> while holding both of these locks.
> 
> Signed-off-by: Michal Kazior <michal.kazior@tieto.com>
> ---

Applied to my mac80211-next-csa.git tree.

--
Luca.

Re: [PATCH] mac80211: protect AP VLAN list with local->mtx

[Johannes Berg]

On Wed, 2014-03-05 at 13:14 +0100, Michal Kazior wrote:
> It was impossible to change chanctx of master AP
> for AP VLANs because the copy function requires
> RTNL which can't be simply taken in mac80211 code
> due to possible deadlocks.
> 
> This is required for future chanctx reservation
> that re-bind vifs to new chanctx. This requires
> safe AP VLAN iteration without RTNL.
> 
> Now VLANs can be iterated while holding either
> RTNL or local->mtx because the list is modified
> while holding both of these locks.

No objection really, but maybe it would make more sense to use
iflist_mtx?

johannes

Re: [PATCH] mac80211: protect AP VLAN list with local->mtx

[Michal Kazior]

On 19 March 2014 15:06, Johannes Berg <johannes@sipsolutions.net> wrote:
> On Wed, 2014-03-05 at 13:14 +0100, Michal Kazior wrote:
>> It was impossible to change chanctx of master AP
>> for AP VLANs because the copy function requires
>> RTNL which can't be simply taken in mac80211 code
>> due to possible deadlocks.
>>
>> This is required for future chanctx reservation
>> that re-bind vifs to new chanctx. This requires
>> safe AP VLAN iteration without RTNL.
>>
>> Now VLANs can be iterated while holding either
>> RTNL or local->mtx because the list is modified
>> while holding both of these locks.
>
> No objection really, but maybe it would make more sense to use
> iflist_mtx?

I used local->mtx because it seemed easier at the time (the lock is
already used on all related codepaths).

Using local->iflist_mtx would add another mutex to for
csa/reservation. I think it shouldn't be hard to do it though. Should
I re-spin? (this will probably need a re-spin of Luca's reservation
patchset and my RFC).


Michał

Re: [PATCH] mac80211: protect AP VLAN list with local->mtx

[Johannes Berg]

On Thu, 2014-03-20 at 08:12 +0100, Michal Kazior wrote:
> On 19 March 2014 15:06, Johannes Berg <johannes@sipsolutions.net> wrote:
> > On Wed, 2014-03-05 at 13:14 +0100, Michal Kazior wrote:
> >> It was impossible to change chanctx of master AP
> >> for AP VLANs because the copy function requires
> >> RTNL which can't be simply taken in mac80211 code
> >> due to possible deadlocks.
> >>
> >> This is required for future chanctx reservation
> >> that re-bind vifs to new chanctx. This requires
> >> safe AP VLAN iteration without RTNL.
> >>
> >> Now VLANs can be iterated while holding either
> >> RTNL or local->mtx because the list is modified
> >> while holding both of these locks.
> >
> > No objection really, but maybe it would make more sense to use
> > iflist_mtx?
> 
> I used local->mtx because it seemed easier at the time (the lock is
> already used on all related codepaths).
> 
> Using local->iflist_mtx would add another mutex to for
> csa/reservation. I think it shouldn't be hard to do it though. Should
> I re-spin? (this will probably need a re-spin of Luca's reservation
> patchset and my RFC).

No, it's fine, I was just curious.

johannes