cfg80211: avoid holding the RTNL when calling the driver

Currently, _everything_ in cfg80211 holds the RTNL, and if you
have a slow USB device (or a few) you can get some bad lock
contention on that.

Fix that by re-adding a mutex to each wiphy/rdev as we had at
some point, so we have locking for the wireless_dev lists and
all the other things in there, and also so that drivers still
don't have to worry too much about it (they still won't get
parallel calls for a single device).

Then, we can restrict the RTNL to a few cases where we add or
remove interfaces and really need the added protection. Some
of the global list management still also uses the RTNL, since
we need to have it anyway for netdev management, but we only
hold the RTNL for very short periods of time here.

Link: https://lore.kernel.org/r/20210122161942.81df9f5e047a.I4a8e1a60b18863ea8c5e6d3a0faeafb2d45b2f40@changeid
Tested-by: Marek Szyprowski <m.szyprowski@samsung.com> [marvell driver issues]
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

1 files changed, 61 insertions, 30 deletions

diff --git a/net/wireless/reg.c b/net/wireless/reg.c
index 8114bba8556c..452b698f42be 100644
--- a/net/wireless/reg.c
+++ b/net/wireless/reg.c
@@ -142,12 +142,15 @@ static const struct ieee80211_regdomain *get_cfg80211_regdom(void)
 /*
  * Returns the regulatory domain associated with the wiphy.
  *
- * Requires either RTNL or RCU protection
+ * Requires any of RTNL, wiphy mutex or RCU protection.
  */
 const struct ieee80211_regdomain *get_wiphy_regdom(struct wiphy *wiphy)
 {
-	return rcu_dereference_rtnl(wiphy->regd);
+	return rcu_dereference_check(wiphy->regd,
+				     lockdep_is_held(&wiphy->mtx) ||
+				     lockdep_rtnl_is_held());
 }
+EXPORT_SYMBOL(get_wiphy_regdom);
 
 static const char *reg_dfs_region_str(enum nl80211_dfs_regions dfs_region)
 {
@@ -169,7 +172,9 @@ enum nl80211_dfs_regions reg_get_dfs_region(struct wiphy *wiphy)
 	const struct ieee80211_regdomain *regd = NULL;
 	const struct ieee80211_regdomain *wiphy_regd = NULL;
 
+	rcu_read_lock();
 	regd = get_cfg80211_regdom();
+
 	if (!wiphy)
 		goto out;
 
@@ -186,6 +191,8 @@ enum nl80211_dfs_regions reg_get_dfs_region(struct wiphy *wiphy)
 		 reg_dfs_region_str(regd->dfs_region));
 
 out:
+	rcu_read_unlock();
+
 	return regd->dfs_region;
 }
 
@@ -2577,11 +2584,13 @@ void wiphy_apply_custom_regulatory(struct wiphy *wiphy,
 		return;
 
 	rtnl_lock();
+	wiphy_lock(wiphy);
 
 	tmp = get_wiphy_regdom(wiphy);
 	rcu_assign_pointer(wiphy->regd, new_regd);
 	rcu_free_regdom(tmp);
 
+	wiphy_unlock(wiphy);
 	rtnl_unlock();
 }
 EXPORT_SYMBOL(wiphy_apply_custom_regulatory);
@@ -2744,7 +2753,10 @@ reg_process_hint_driver(struct wiphy *wiphy,
 			return REG_REQ_IGNORE;
 
 		tmp = get_wiphy_regdom(wiphy);
+		ASSERT_RTNL();
+		wiphy_lock(wiphy);
 		rcu_assign_pointer(wiphy->regd, regd);
+		wiphy_unlock(wiphy);
 		rcu_free_regdom(tmp);
 	}
 
@@ -3076,41 +3088,52 @@ static void reg_process_pending_beacon_hints(void)
 	spin_unlock_bh(&reg_pending_beacons_lock);
 }
 
-static void reg_process_self_managed_hints(void)
+static void reg_process_self_managed_hint(struct wiphy *wiphy)
 {
-	struct cfg80211_registered_device *rdev;
-	struct wiphy *wiphy;
+	struct cfg80211_registered_device *rdev = wiphy_to_rdev(wiphy);
 	const struct ieee80211_regdomain *tmp;
 	const struct ieee80211_regdomain *regd;
 	enum nl80211_band band;
 	struct regulatory_request request = {};
 
-	list_for_each_entry(rdev, &cfg80211_rdev_list, list) {
-		wiphy = &rdev->wiphy;
+	ASSERT_RTNL();
+	lockdep_assert_wiphy(wiphy);
 
-		spin_lock(&reg_requests_lock);
-		regd = rdev->requested_regd;
-		rdev->requested_regd = NULL;
-		spin_unlock(&reg_requests_lock);
+	spin_lock(&reg_requests_lock);
+	regd = rdev->requested_regd;
+	rdev->requested_regd = NULL;
+	spin_unlock(&reg_requests_lock);
 
-		if (regd == NULL)
-			continue;
+	if (!regd)
+		return;
 
-		tmp = get_wiphy_regdom(wiphy);
-		rcu_assign_pointer(wiphy->regd, regd);
-		rcu_free_regdom(tmp);
+	tmp = get_wiphy_regdom(wiphy);
+	rcu_assign_pointer(wiphy->regd, regd);
+	rcu_free_regdom(tmp);
+
+	for (band = 0; band < NUM_NL80211_BANDS; band++)
+		handle_band_custom(wiphy, wiphy->bands[band], regd);
 
-		for (band = 0; band < NUM_NL80211_BANDS; band++)
-			handle_band_custom(wiphy, wiphy->bands[band], regd);
+	reg_process_ht_flags(wiphy);
 
-		reg_process_ht_flags(wiphy);
+	request.wiphy_idx = get_wiphy_idx(wiphy);
+	request.alpha2[0] = regd->alpha2[0];
+	request.alpha2[1] = regd->alpha2[1];
+	request.initiator = NL80211_REGDOM_SET_BY_DRIVER;
 
-		request.wiphy_idx = get_wiphy_idx(wiphy);
-		request.alpha2[0] = regd->alpha2[0];
-		request.alpha2[1] = regd->alpha2[1];
-		request.initiator = NL80211_REGDOM_SET_BY_DRIVER;
+	nl80211_send_wiphy_reg_change_event(&request);
+}
 
-		nl80211_send_wiphy_reg_change_event(&request);
+static void reg_process_self_managed_hints(void)
+{
+	struct cfg80211_registered_device *rdev;
+
+	ASSERT_RTNL();
+
+	list_for_each_entry(rdev, &cfg80211_rdev_list, list) {
+		wiphy_lock(&rdev->wiphy);
+		reg_process_self_managed_hint(&rdev->wiphy);
+		wiphy_unlock(&rdev->wiphy);
 	}
 
 	reg_check_channels();
@@ -3789,14 +3812,21 @@ static int reg_set_rd_driver(const struct ieee80211_regdomain *rd,
 		return -ENODEV;
 
 	if (!driver_request->intersect) {
-		if (request_wiphy->regd)
+		ASSERT_RTNL();
+		wiphy_lock(request_wiphy);
+		if (request_wiphy->regd) {
+			wiphy_unlock(request_wiphy);
 			return -EALREADY;
+		}
 
 		regd = reg_copy_regd(rd);
-		if (IS_ERR(regd))
+		if (IS_ERR(regd)) {
+			wiphy_unlock(request_wiphy);
 			return PTR_ERR(regd);
+		}
 
 		rcu_assign_pointer(request_wiphy->regd, regd);
+		wiphy_unlock(request_wiphy);
 		reset_regdomains(false, rd);
 		return 0;
 	}
@@ -3978,8 +4008,8 @@ int regulatory_set_wiphy_regd(struct wiphy *wiphy,
 }
 EXPORT_SYMBOL(regulatory_set_wiphy_regd);
 
-int regulatory_set_wiphy_regd_sync_rtnl(struct wiphy *wiphy,
-					struct ieee80211_regdomain *rd)
+int regulatory_set_wiphy_regd_sync(struct wiphy *wiphy,
+				   struct ieee80211_regdomain *rd)
 {
 	int ret;
 
@@ -3990,10 +4020,11 @@ int regulatory_set_wiphy_regd_sync_rtnl(struct wiphy *wiphy,
 		return ret;
 
 	/* process the request immediately */
-	reg_process_self_managed_hints();
+	reg_process_self_managed_hint(wiphy);
+	reg_check_channels();
 	return 0;
 }
-EXPORT_SYMBOL(regulatory_set_wiphy_regd_sync_rtnl);
+EXPORT_SYMBOL(regulatory_set_wiphy_regd_sync);
 
 void wiphy_regulatory_register(struct wiphy *wiphy)
 {