[PATCH] mac80211: fix virtual interface locking

Florian Lohoff noticed a bug in mac80211: when bringing the
master interface down while other virtual interfaces are up
we call dev_close() under a spinlock which is not allowed.
This patch removes the sub_if_lock used by mac80211 in favour
of using an RCU list. All list manipulations are already done
under rtnl so are well protected against each other, and the
read-side locks we took in the RX and TX code are already in
RCU read-side critical sections.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Cc: Florian Lohoff <flo@rfc822.org>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: Michal Piotrowski <michal.k.k.piotrowski@gmail.com>
Cc: Satyam Sharma <satyam@infradead.org>
Signed-off-by: Michael Wu <flamingice@sourmilk.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

diff --git a/net/mac80211/ieee80211.c b/net/mac80211/ieee80211.c
index 4e345f8..ccf8463 100644 (file)
--- a/net/mac80211/ieee80211.c
+++ b/net/mac80211/ieee80211.c
@@ -93,14 +93,13 @@ static int ieee80211_master_open(struct net_device *dev)
        struct ieee80211_sub_if_data *sdata;
        int res = -EOPNOTSUPP;
 
-       read_lock(&local->sub_if_lock);
-       list_for_each_entry(sdata, &local->sub_if_list, list) {
+       /* we hold the RTNL here so can safely walk the list */
+       list_for_each_entry(sdata, &local->interfaces, list) {
                if (sdata->dev != dev && netif_running(sdata->dev)) {
                        res = 0;
                        break;
                }
        }
-       read_unlock(&local->sub_if_lock);
        return res;
 }
 
@@ -109,11 +108,10 @@ static int ieee80211_master_stop(struct net_device *dev)
        struct ieee80211_local *local = wdev_priv(dev->ieee80211_ptr);
        struct ieee80211_sub_if_data *sdata;
 
-       read_lock(&local->sub_if_lock);
-       list_for_each_entry(sdata, &local->sub_if_list, list)
+       /* we hold the RTNL here so can safely walk the list */
+       list_for_each_entry(sdata, &local->interfaces, list)
                if (sdata->dev != dev && netif_running(sdata->dev))
                        dev_close(sdata->dev);
-       read_unlock(&local->sub_if_lock);
 
        return 0;
 }
@@ -315,8 +313,8 @@ static int ieee80211_open(struct net_device *dev)
 
        sdata = IEEE80211_DEV_TO_SUB_IF(dev);
 
-       read_lock(&local->sub_if_lock);
-       list_for_each_entry(nsdata, &local->sub_if_list, list) {
+       /* we hold the RTNL here so can safely walk the list */
+       list_for_each_entry(nsdata, &local->interfaces, list) {
                struct net_device *ndev = nsdata->dev;
 
                if (ndev != dev && ndev != local->mdev && netif_running(ndev) &&
@@ -325,10 +323,8 @@ static int ieee80211_open(struct net_device *dev)
                         * check whether it may have the same address
                         */
                        if (!identical_mac_addr_allowed(sdata->type,
-                                                       nsdata->type)) {
-                               read_unlock(&local->sub_if_lock);
+                                                       nsdata->type))
                                return -ENOTUNIQ;
-                       }
 
                        /*
                         * can only add VLANs to enabled APs
@@ -339,7 +335,6 @@ static int ieee80211_open(struct net_device *dev)
                                sdata->u.vlan.ap = nsdata;
                }
        }
-       read_unlock(&local->sub_if_lock);
 
        switch (sdata->type) {
        case IEEE80211_IF_TYPE_WDS:
@@ -466,14 +461,13 @@ static int ieee80211_stop(struct net_device *dev)
                sdata->u.sta.state = IEEE80211_DISABLED;
                del_timer_sync(&sdata->u.sta.timer);
                /*
-                * Holding the sub_if_lock for writing here blocks
-                * out the receive path and makes sure it's not
-                * currently processing a packet that may get
-                * added to the queue.
+                * When we get here, the interface is marked down.
+                * Call synchronize_rcu() to wait for the RX path
+                * should it be using the interface and enqueuing
+                * frames at this very time on another CPU.
                 */
-               write_lock_bh(&local->sub_if_lock);
+               synchronize_rcu();
                skb_queue_purge(&sdata->u.sta.skb_queue);
-               write_unlock_bh(&local->sub_if_lock);
 
                if (!local->ops->hw_scan &&
                    local->scan_dev == sdata->dev) {
@@ -1033,9 +1027,9 @@ void ieee80211_tx_status(struct ieee80211_hw *hw, struct sk_buff *skb,
 
        rthdr->data_retries = status->retry_count;
 
-       read_lock(&local->sub_if_lock);
+       rcu_read_lock();
        monitors = local->monitors;
-       list_for_each_entry(sdata, &local->sub_if_list, list) {
+       list_for_each_entry_rcu(sdata, &local->interfaces, list) {
                /*
                 * Using the monitors counter is possibly racy, but
                 * if the value is wrong we simply either clone the skb
@@ -1051,7 +1045,7 @@ void ieee80211_tx_status(struct ieee80211_hw *hw, struct sk_buff *skb,
                                continue;
                        monitors--;
                        if (monitors)
-                               skb2 = skb_clone(skb, GFP_KERNEL);
+                               skb2 = skb_clone(skb, GFP_ATOMIC);
                        else
                                skb2 = NULL;
                        skb->dev = sdata->dev;
@@ -1066,7 +1060,7 @@ void ieee80211_tx_status(struct ieee80211_hw *hw, struct sk_buff *skb,
                }
        }
  out:
-       read_unlock(&local->sub_if_lock);
+       rcu_read_unlock();
        if (skb)
                dev_kfree_skb(skb);
 }
@@ -1154,8 +1148,7 @@ struct ieee80211_hw *ieee80211_alloc_hw(size_t priv_data_len,
 
        INIT_LIST_HEAD(&local->modes_list);
 
-       rwlock_init(&local->sub_if_lock);
-       INIT_LIST_HEAD(&local->sub_if_list);
+       INIT_LIST_HEAD(&local->interfaces);
 
        INIT_DELAYED_WORK(&local->scan_work, ieee80211_sta_scan_work);
        ieee80211_rx_bss_list_init(mdev);
@@ -1175,7 +1168,8 @@ struct ieee80211_hw *ieee80211_alloc_hw(size_t priv_data_len,
        sdata->u.ap.force_unicast_rateidx = -1;
        sdata->u.ap.max_ratectrl_rateidx = -1;
        ieee80211_if_sdata_init(sdata);
-       list_add_tail(&sdata->list, &local->sub_if_list);
+       /* no RCU needed since we're still during init phase */
+       list_add_tail(&sdata->list, &local->interfaces);
 
        tasklet_init(&local->tx_pending_tasklet, ieee80211_tx_pending,
                     (unsigned long)local);
@@ -1334,7 +1328,6 @@ void ieee80211_unregister_hw(struct ieee80211_hw *hw)
 {
        struct ieee80211_local *local = hw_to_local(hw);
        struct ieee80211_sub_if_data *sdata, *tmp;
-       struct list_head tmp_list;
        int i;
 
        tasklet_kill(&local->tx_pending_tasklet);
@@ -1348,11 +1341,12 @@ void ieee80211_unregister_hw(struct ieee80211_hw *hw)
        if (local->apdev)
                ieee80211_if_del_mgmt(local);
 
-       write_lock_bh(&local->sub_if_lock);
-       list_replace_init(&local->sub_if_list, &tmp_list);
-       write_unlock_bh(&local->sub_if_lock);
-
-       list_for_each_entry_safe(sdata, tmp, &tmp_list, list)
+       /*
+        * At this point, interface list manipulations are fine
+        * because the driver cannot be handing us frames any
+        * more and the tasklet is killed.
+        */
+       list_for_each_entry_safe(sdata, tmp, &local->interfaces, list)
                __ieee80211_if_del(local, sdata);
 
        rtnl_unlock();

diff --git a/net/mac80211/ieee80211_i.h b/net/mac80211/ieee80211_i.h
index 1a43f3e..a5961f1 100644 (file)
--- a/net/mac80211/ieee80211_i.h
+++ b/net/mac80211/ieee80211_i.h
@@ -475,9 +475,8 @@ struct ieee80211_local {
        ieee80211_rx_handler *rx_handlers;
        ieee80211_tx_handler *tx_handlers;
 
-       rwlock_t sub_if_lock; /* Protects sub_if_list. Cannot be taken under
-                              * sta_bss_lock or sta_lock. */
-       struct list_head sub_if_list;
+       struct list_head interfaces;
+
        int sta_scanning;
        int scan_channel_idx;
        enum { SCAN_SET_CHANNEL, SCAN_SEND_PROBE } scan_state;

diff --git a/net/mac80211/ieee80211_iface.c b/net/mac80211/ieee80211_iface.c
index 4590205..2ba24ef 100644 (file)
--- a/net/mac80211/ieee80211_iface.c
+++ b/net/mac80211/ieee80211_iface.c
@@ -79,16 +79,15 @@ int ieee80211_if_add(struct net_device *dev, const char *name,
        ieee80211_debugfs_add_netdev(sdata);
        ieee80211_if_set_type(ndev, type);
 
-       write_lock_bh(&local->sub_if_lock);
+       /* we're under RTNL so all this is fine */
        if (unlikely(local->reg_state == IEEE80211_DEV_UNREGISTERED)) {
-               write_unlock_bh(&local->sub_if_lock);
                __ieee80211_if_del(local, sdata);
                return -ENODEV;
        }
-       list_add(&sdata->list, &local->sub_if_list);
+       list_add_tail_rcu(&sdata->list, &local->interfaces);
+
        if (new_dev)
                *new_dev = ndev;
-       write_unlock_bh(&local->sub_if_lock);
 
        return 0;
 
@@ -226,22 +225,22 @@ void ieee80211_if_reinit(struct net_device *dev)
                /* Remove all virtual interfaces that use this BSS
                 * as their sdata->bss */
                struct ieee80211_sub_if_data *tsdata, *n;
-               LIST_HEAD(tmp_list);
 
-               write_lock_bh(&local->sub_if_lock);
-               list_for_each_entry_safe(tsdata, n, &local->sub_if_list, list) {
+               list_for_each_entry_safe(tsdata, n, &local->interfaces, list) {
                        if (tsdata != sdata && tsdata->bss == &sdata->u.ap) {
                                printk(KERN_DEBUG "%s: removing virtual "
                                       "interface %s because its BSS interface"
                                       " is being removed\n",
                                       sdata->dev->name, tsdata->dev->name);
-                               list_move_tail(&tsdata->list, &tmp_list);
+                               list_del_rcu(&tsdata->list);
+                               /*
+                                * We have lots of time and can afford
+                                * to sync for each interface
+                                */
+                               synchronize_rcu();
+                               __ieee80211_if_del(local, tsdata);
                        }
                }
-               write_unlock_bh(&local->sub_if_lock);
-
-               list_for_each_entry_safe(tsdata, n, &tmp_list, list)
-                       __ieee80211_if_del(local, tsdata);
 
                kfree(sdata->u.ap.beacon_head);
                kfree(sdata->u.ap.beacon_tail);
@@ -318,18 +317,16 @@ int ieee80211_if_remove(struct net_device *dev, const char *name, int id)
 
        ASSERT_RTNL();
 
-       write_lock_bh(&local->sub_if_lock);
-       list_for_each_entry_safe(sdata, n, &local->sub_if_list, list) {
+       list_for_each_entry_safe(sdata, n, &local->interfaces, list) {
                if ((sdata->type == id || id == -1) &&
                    strcmp(name, sdata->dev->name) == 0 &&
                    sdata->dev != local->mdev) {
-                       list_del(&sdata->list);
-                       write_unlock_bh(&local->sub_if_lock);
+                       list_del_rcu(&sdata->list);
+                       synchronize_rcu();
                        __ieee80211_if_del(local, sdata);
                        return 0;
                }
        }
-       write_unlock_bh(&local->sub_if_lock);
        return -ENODEV;
 }
 

diff --git a/net/mac80211/ieee80211_sta.c b/net/mac80211/ieee80211_sta.c
index 17455c6..651aaba 100644 (file)
--- a/net/mac80211/ieee80211_sta.c
+++ b/net/mac80211/ieee80211_sta.c
@@ -2676,8 +2676,8 @@ void ieee80211_scan_completed(struct ieee80211_hw *hw)
        memset(&wrqu, 0, sizeof(wrqu));
        wireless_send_event(dev, SIOCGIWSCAN, &wrqu, NULL);
 
-       read_lock(&local->sub_if_lock);
-       list_for_each_entry(sdata, &local->sub_if_list, list) {
+       rcu_read_lock();
+       list_for_each_entry_rcu(sdata, &local->interfaces, list) {
 
                /* No need to wake the master device. */
                if (sdata->dev == local->mdev)
@@ -2691,7 +2691,7 @@ void ieee80211_scan_completed(struct ieee80211_hw *hw)
 
                netif_wake_queue(sdata->dev);
        }
-       read_unlock(&local->sub_if_lock);
+       rcu_read_unlock();
 
        sdata = IEEE80211_DEV_TO_SUB_IF(dev);
        if (sdata->type == IEEE80211_IF_TYPE_IBSS) {
@@ -2828,8 +2828,8 @@ static int ieee80211_sta_start_scan(struct net_device *dev,
 
        local->sta_scanning = 1;
 
-       read_lock(&local->sub_if_lock);
-       list_for_each_entry(sdata, &local->sub_if_list, list) {
+       rcu_read_lock();
+       list_for_each_entry_rcu(sdata, &local->interfaces, list) {
 
                /* Don't stop the master interface, otherwise we can't transmit
                 * probes! */
@@ -2841,7 +2841,7 @@ static int ieee80211_sta_start_scan(struct net_device *dev,
                    (sdata->u.sta.flags & IEEE80211_STA_ASSOCIATED))
                        ieee80211_send_nullfunc(local, sdata, 1);
        }
-       read_unlock(&local->sub_if_lock);
+       rcu_read_unlock();
 
        if (ssid) {
                local->scan_ssid_len = ssid_len;

diff --git a/net/mac80211/rx.c b/net/mac80211/rx.c
index 2535d8d..cb44a9d 100644 (file)
--- a/net/mac80211/rx.c
+++ b/net/mac80211/rx.c
@@ -1383,8 +1383,9 @@ void __ieee80211_rx(struct ieee80211_hw *hw, struct sk_buff *skb,
        }
 
        /*
-        * key references are protected using RCU and this requires that
-        * we are in a read-site RCU section during receive processing
+        * key references and virtual interfaces are protected using RCU
+        * and this requires that we are in a read-side RCU section during
+        * receive processing
         */
        rcu_read_lock();
 
@@ -1439,8 +1440,7 @@ void __ieee80211_rx(struct ieee80211_hw *hw, struct sk_buff *skb,
 
        bssid = ieee80211_get_bssid(hdr, skb->len - radiotap_len);
 
-       read_lock(&local->sub_if_lock);
-       list_for_each_entry(sdata, &local->sub_if_list, list) {
+       list_for_each_entry_rcu(sdata, &local->interfaces, list) {
                rx.flags |= IEEE80211_TXRXD_RXRA_MATCH;
 
                if (!netif_running(sdata->dev))
@@ -1493,7 +1493,6 @@ void __ieee80211_rx(struct ieee80211_hw *hw, struct sk_buff *skb,
                                             &rx, sta);
        } else
                dev_kfree_skb(skb);
-       read_unlock(&local->sub_if_lock);
 
  end:
        rcu_read_unlock();

diff --git a/net/mac80211/tx.c b/net/mac80211/tx.c
index 38394c4..244c80d 100644 (file)
--- a/net/mac80211/tx.c
+++ b/net/mac80211/tx.c
@@ -295,8 +295,12 @@ static void purge_old_ps_buffers(struct ieee80211_local *local)
        struct ieee80211_sub_if_data *sdata;
        struct sta_info *sta;
 
-       read_lock(&local->sub_if_lock);
-       list_for_each_entry(sdata, &local->sub_if_list, list) {
+       /*
+        * virtual interfaces are protected by RCU
+        */
+       rcu_read_lock();
+
+       list_for_each_entry_rcu(sdata, &local->interfaces, list) {
                struct ieee80211_if_ap *ap;
                if (sdata->dev == local->mdev ||
                    sdata->type != IEEE80211_IF_TYPE_AP)
@@ -309,7 +313,7 @@ static void purge_old_ps_buffers(struct ieee80211_local *local)
                }
                total += skb_queue_len(&ap->ps_bc_buf);
        }
-       read_unlock(&local->sub_if_lock);
+       rcu_read_unlock();
 
        read_lock_bh(&local->sta_lock);
        list_for_each_entry(sta, &local->sta_list, list) {