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

From: Johannes Berg
Date: Thu Sep 06 2007 - 09:35:59 EST

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.

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);
+
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);
- 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();

- 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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