Re: BUG: scheduling while atomic: ifconfig/0x00000002/4170

Paul E. McKenney
2007-09-06T15:46:29Z

On Thu, Sep 06, 2007 at 03:36:55PM +0200, Johannes Berg wrote:
> On Thu, 2007-09-06 at 20:36 +0800, Herbert Xu wrote:
>
> > Yeah I think they're all under RTNL too. So you don't need to
> > take the lock here at all since you should already have the RTNL.
>
> Ok, this patch gets rid of the lock. I'd appreciate if you could give it
> a quick look for obvious RCU abuse as I haven't tested it. It also
> doesn't apply against net-2.6.24 because I based it after the patches I
> have queued with John for net-2.6.24.

Looks good to me from an RCU viewpoint. I cannot claim familiarity with
this code. I therefore especially like the indications of where RTNL
is held and not!!!

Some questions below based on a quick scan. And a global question:
should the comments about RTNL being held be replaced by ASSERT_RTNL()?

Thanx, Paul

> johannes
>
> --- netdev-2.6.orig/net/mac80211/ieee80211.c 2007-09-06 15:35:23.324447686 +0200
> +++ netdev-2.6/net/mac80211/ieee80211.c 2007-09-06 15:35:23.394447686 +0200
> @@ -90,8 +90,9 @@ static struct dev_mc_list *ieee80211_get
>
> /* start of iteration, both unassigned */
> if (!mcd->cur && !mcd->sdata) {
> - mcd->sdata = list_entry(local->sub_if_list.next,
> - struct ieee80211_sub_if_data, list);
> + mcd->sdata = list_entry(
> + rcu_dereference(local->interfaces.next),
> + struct ieee80211_sub_if_data, list);
> mcd->cur = mcd->sdata->dev->mc_list;
> }
>
> @@ -100,10 +101,11 @@ static struct dev_mc_list *ieee80211_get
>
> while (!mcd->cur) {
> /* reached end of interface list? */
> - if (mcd->sdata->list.next == &local->sub_if_list)
> + if (rcu_dereference(mcd->sdata->list.next) ==
> + &local->interfaces)
> break;
> /* otherwise try next interface */
> - mcd->sdata = list_entry(mcd->sdata->list.next,
> + mcd->sdata = list_entry(rcu_dereference(mcd->sdata->list.next),
> struct ieee80211_sub_if_data, list);
> mcd->cur = mcd->sdata->dev->mc_list;
> }
> @@ -145,9 +147,10 @@ static void ieee80211_configure_filter(s
>
> /*
> * We can iterate through the device list for the multicast
> - * address list so need to lock it.
> + * address list so need to be in a RCU read-side section,
> + * the RTNL isn't held in this function.
> */
> - read_lock(&local->sub_if_lock);
> + rcu_read_lock();
>
> /* be a bit nasty */
> new_flags |= (1<<31);
> @@ -163,7 +166,7 @@ static void ieee80211_configure_filter(s
> WARN_ON(mcd.cur);
>
> local->filter_flags = new_flags & ~(1<<31);
> - read_unlock(&local->sub_if_lock);
> + rcu_read_unlock();
>
> netif_tx_unlock(local->mdev);
> }
> @@ -176,14 +179,13 @@ static int ieee80211_master_open(struct
> 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;
> }
>
> @@ -192,11 +194,10 @@ static int ieee80211_master_stop(struct
> 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;
> }
> @@ -430,8 +431,8 @@ static int ieee80211_open(struct net_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) &&
> @@ -440,10 +441,8 @@ static int ieee80211_open(struct net_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
> @@ -454,7 +453,6 @@ static int ieee80211_open(struct net_dev
> sdata->u.vlan.ap = nsdata;
> }
> }
> - read_unlock(&local->sub_if_lock);
>
> switch (sdata->type) {
> case IEEE80211_IF_TYPE_WDS:
> @@ -575,14 +573,13 @@ static int ieee80211_stop(struct net_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) {
> @@ -1134,9 +1131,9 @@ void ieee80211_tx_status(struct ieee8021
>
> 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
> @@ -1152,7 +1149,7 @@ void ieee80211_tx_status(struct ieee8021
> continue;
> monitors--;
> if (monitors)
> - skb2 = skb_clone(skb, GFP_KERNEL);
> + skb2 = skb_clone(skb, GFP_ATOMIC);
> else
> skb2 = NULL;
> skb->dev = sdata->dev;
> @@ -1167,7 +1164,7 @@ void ieee80211_tx_status(struct ieee8021
> }
> }
> out:
> - read_unlock(&local->sub_if_lock);
> + rcu_read_unlock();
> if (skb)
> dev_kfree_skb(skb);
> }
> @@ -1255,8 +1252,7 @@ struct ieee80211_hw *ieee80211_alloc_hw(
>
> 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);
> @@ -1275,7 +1271,8 @@ struct ieee80211_hw *ieee80211_alloc_hw(
> 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);
> @@ -1434,7 +1431,6 @@ void ieee80211_unregister_hw(struct ieee
> {
> 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);
> @@ -1448,11 +1444,12 @@ void ieee80211_unregister_hw(struct ieee
> 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();
> --- netdev-2.6.orig/net/mac80211/ieee80211_i.h 2007-09-06 15:35:23.334447686 +0200
> +++ netdev-2.6/net/mac80211/ieee80211_i.h 2007-09-06 15:35:23.404447686 +0200
> @@ -481,9 +481,8 @@ 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;
> --- netdev-2.6.orig/net/mac80211/ieee80211_iface.c 2007-09-06 15:35:23.334447686 +0200
> +++ netdev-2.6/net/mac80211/ieee80211_iface.c 2007-09-06 15:35:23.404447686 +0200
> @@ -79,16 +79,15 @@ int ieee80211_if_add(struct net_device *
> 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);

The _rcu is required because this list isn't protected by RTNL?

> +
> 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_devi
> /* 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);

This code is also protected by RTNL?

> - 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_devic
>
> ASSERT_RTNL();

I -like- this!!! ;-)

> - 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;
> }
>
> --- netdev-2.6.orig/net/mac80211/ieee80211_sta.c 2007-09-06 15:35:23.224447686 +0200
> +++ netdev-2.6/net/mac80211/ieee80211_sta.c 2007-09-06 15:35:23.414447686 +0200
> @@ -2659,8 +2659,8 @@ void ieee80211_scan_completed(struct iee
> 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)
> @@ -2674,7 +2674,7 @@ void ieee80211_scan_completed(struct iee
>
> 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) {
> @@ -2811,8 +2811,8 @@ static int ieee80211_sta_start_scan(stru
>
> 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! */
> @@ -2824,7 +2824,7 @@ static int ieee80211_sta_start_scan(stru
> (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;
> --- netdev-2.6.orig/net/mac80211/rx.c 2007-09-06 15:35:23.214447686 +0200
> +++ netdev-2.6/net/mac80211/rx.c 2007-09-06 15:35:23.414447686 +0200
> @@ -1385,8 +1385,9 @@ void __ieee80211_rx(struct ieee80211_hw
> }
>
> /*
> - * 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();
>
> @@ -1441,8 +1442,7 @@ void __ieee80211_rx(struct ieee80211_hw
>
> 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))
> @@ -1494,7 +1494,6 @@ void __ieee80211_rx(struct ieee80211_hw
> &rx, sta);
> } else
> dev_kfree_skb(skb);
> - read_unlock(&local->sub_if_lock);
>
> end:
> rcu_read_unlock();
> --- netdev-2.6.orig/net/mac80211/tx.c 2007-09-06 15:35:23.074447686 +0200
> +++ netdev-2.6/net/mac80211/tx.c 2007-09-06 15:35:23.424447686 +0200
> @@ -291,8 +291,12 @@ static void purge_old_ps_buffers(struct
> 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)
> @@ -305,7 +309,7 @@ static void purge_old_ps_buffers(struct
> }
> 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) {
>
>
> -
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