From: John Linville <linville@redhat.com>
Date: Wed, 2 Dec 2009 15:39:26 -0500
Subject: [net] wireless: avoid deadlock when enabling rfkill
Message-id: <20091202153926.GA30909@redhat.com>
Patchwork-id: 21652
O-Subject: [RHEL5.5 PATCH] wireless: avoid deadlock when enabling rfkill
Bugzilla: 542593
RH-Acked-by: David S. Miller <davem@redhat.com>

The wireless update from 2.6.32 has a deadlock when enabling rfkill.
I introduced this in the backport while trying to avoid another
issue. :-(

This patch more-or-less restores the original code (w/o my busted
work-around), but moves a work item to a private workqueue.

BZ542593

 net/wireless/core.c |   27 ++++++++++++++++++---------
 1 files changed, 18 insertions(+), 9 deletions(-)

Tested by me and Stanislaw with positive results.

Signed-off-by: Don Zickus <dzickus@redhat.com>

diff --git a/net/wireless/core.c b/net/wireless/core.c
index 6a6119a..911909d 100644
--- a/net/wireless/core.c
+++ b/net/wireless/core.c
@@ -29,6 +29,9 @@ MODULE_AUTHOR("Johannes Berg");
 MODULE_LICENSE("GPL");
 MODULE_DESCRIPTION("wireless configuration support");
 
+/* Global workqueue for cleanup_work */
+static struct workqueue_struct *workqueue;
+
 /* RCU might be appropriate here since we usually
  * only read the list, and that can happen quite
  * often because we need to do it for each command */
@@ -631,7 +634,6 @@ void wiphy_rfkill_set_hw_state(struct wiphy *wiphy, bool blocked)
 }
 EXPORT_SYMBOL(wiphy_rfkill_set_hw_state);
 
-#if 0 /* Not in RHEL5... */
 static void wdev_cleanup_work(void *w)
 {
 	struct wireless_dev *wdev = w;
@@ -656,7 +658,6 @@ static void wdev_cleanup_work(void *w)
 
 	dev_put(wdev->netdev);
 }
-#endif
 
 static int cfg80211_netdev_notifier_call(struct notifier_block * nb,
 					 unsigned long state,
@@ -681,9 +682,7 @@ static int cfg80211_netdev_notifier_call(struct notifier_block * nb,
 		 * are added with nl80211.
 		 */
 		mutex_init(&wdev->mtx);
-#if 0 /* Not in RHEL5... */
 		INIT_WORK(&wdev->cleanup_work, wdev_cleanup_work, wdev);
-#endif
 		INIT_LIST_HEAD(&wdev->event_list);
 		spin_lock_init(&wdev->event_lock);
 		mutex_lock(&rdev->devlist_mtx);
@@ -743,14 +742,11 @@ static int cfg80211_netdev_notifier_call(struct notifier_block * nb,
 		}
 		break;
 	case NETDEV_DOWN:
-#if 0 /* Not in RHEL5... (This and the NETDEV_UP bits cause hangs. -- JWL) */
 		dev_hold(dev);
+#if 0 /* Not in RHEL5... */
 		schedule_work(&wdev->cleanup_work);
 #else
-		mutex_lock(&rdev->devlist_mtx);
-		rdev->opencount--;
-		mutex_unlock(&rdev->devlist_mtx);
-		wake_up(&rdev->dev_wait);
+		queue_work(workqueue, &wdev->cleanup_work);
 #endif
 		break;
 	case NETDEV_UP:
@@ -767,6 +763,14 @@ static int cfg80211_netdev_notifier_call(struct notifier_block * nb,
 			mutex_unlock(&rdev->devlist_mtx);
 			dev_put(dev);
 		}
+#else
+		/*
+		 * Due to lack of infrastructure in RHEL5, simply insist
+		 * that cleanup_work (now on it's own workqueue) has
+		 * finished before we proceed.
+		 */
+		if (test_bit(0, &wdev->cleanup_work.pending))
+			flush_workqueue(workqueue);
 #endif
 #ifdef CONFIG_WIRELESS_EXT
 		cfg80211_lock_rdev(rdev);
@@ -875,6 +879,10 @@ static int __init cfg80211_init(void)
 	if (err)
 		goto out_fail_reg;
 
+	workqueue = create_singlethread_workqueue("cfg80211");
+	if (!workqueue)
+		goto out_fail_reg;
+
 	return 0;
 
 out_fail_reg:
@@ -894,6 +902,7 @@ subsys_initcall(cfg80211_init);
 
 static void cfg80211_exit(void)
 {
+	destroy_workqueue(workqueue);
 	debugfs_remove(ieee80211_debugfs_dir);
 	nl80211_exit();
 	unregister_netdevice_notifier(&cfg80211_netdev_notifier);