iwlwifi: do not cancel delayed work inside spin_lock_irqsave

Calling cancel_delayed_work() from inside
spin_lock_irqsave, introduces a potential deadlock.

As explained by Johannes Berg <johannes@sipsolutions.net>

A - lock
T - timer

phase                   CPU 1           CPU 2
---------------------------------------------

some place that calls
cancel_timer_sync()
(which is the | code)
                                        lock-irq(A)
|                                       "lock-irq"(T)
|                                       "unlock"(T)
|                                       wait(T)
                                        unlock(A)

timer softirq
                        "lock"(T)
                        run(T)
                        "unlock"(T)

irq handler
          lock(A)
          unlock(A)

Now all that again, interleaved, leading to deadlock:

                                        lock-irq(A)
                        "lock"(T)
                         run(T)
IRQ during or maybe
before run(T) -->        lock(A)
                                        "lock-irq"(T)
                                        wait(T)

We fix this by moving the call to cancel_delayed_work() into workqueue.
There are cases where the work may not actually be queued or running
at the time we are trying to cancel it, but cancel_delayed_work() is
able to deal with this.

Also cleanup iwl_set_mode related to this call. This function
(iwl_set_mode) is only called when bringing interface up and there will
thus not be any scanning done. No need to try to cancel scanning.

Fixes http://bugzilla.kernel.org/show_bug.cgi?id=13224, which was also
reported at http://marc.info/?l=linux-wireless&m=124081921903223&w=2 .
Tested-by: NMiles Lane <miles.lane@gmail.com>
Signed-off-by: NReinette Chatre <reinette.chatre@intel.com>
Acked-by: NZhu Yi <yi.zhu@intel.com>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>

drivers/net/wireless/iwlwifi/iwl-agn.c

@@ -669,13 +669,6 @@ static int iwl_set_mode(struct iwl_priv *priv, int mode)
 	if (!iwl_is_ready_rf(priv))
 		return -EAGAIN;
 
-	cancel_delayed_work(&priv->scan_check);
-	if (iwl_scan_cancel_timeout(priv, 100)) {
-		IWL_WARN(priv, "Aborted scan still in progress after 100ms\n");
-		IWL_DEBUG_MAC80211(priv, "leaving - scan abort failed.\n");
-		return -EAGAIN;
-	}
-
 	iwl_commit_rxon(priv);
 
 	return 0;

drivers/net/wireless/iwlwifi/iwl-scan.c

@@ -227,9 +227,6 @@ static void iwl_rx_scan_complete_notif(struct iwl_priv *priv,
 	/* The HW is no longer scanning */
 	clear_bit(STATUS_SCAN_HW, &priv->status);
 
-	/* The scan completion notification came in, so kill that timer... */
-	cancel_delayed_work(&priv->scan_check);
-
 	IWL_DEBUG_INFO(priv, "Scan pass on %sGHz took %dms\n",
 		       (priv->scan_bands & BIT(IEEE80211_BAND_2GHZ)) ?
 						"2.4" : "5.2",
@@ -712,6 +709,8 @@ static void iwl_bg_request_scan(struct work_struct *data)
 
 	mutex_lock(&priv->mutex);
 
+	cancel_delayed_work(&priv->scan_check);
+
 	if (!iwl_is_ready(priv)) {
 		IWL_WARN(priv, "request scan called when driver not ready.\n");
 		goto done;
@@ -925,6 +924,8 @@ void iwl_bg_scan_completed(struct work_struct *work)
 
 	IWL_DEBUG_SCAN(priv, "SCAN complete scan\n");
 
+	cancel_delayed_work(&priv->scan_check);
+
 	ieee80211_scan_completed(priv->hw, false);
 
 	if (test_bit(STATUS_EXIT_PENDING, &priv->status))

drivers/net/wireless/iwlwifi/iwl3945-base.c

@@ -782,13 +782,6 @@ static int iwl3945_set_mode(struct iwl_priv *priv, int mode)
 	if (!iwl_is_ready_rf(priv))
 		return -EAGAIN;
 
-	cancel_delayed_work(&priv->scan_check);
-	if (iwl_scan_cancel_timeout(priv, 100)) {
-		IWL_WARN(priv, "Aborted scan still in progress after 100ms\n");
-		IWL_DEBUG_MAC80211(priv, "leaving - scan abort failed.\n");
-		return -EAGAIN;
-	}
-
 	iwl3945_commit_rxon(priv);
 
 	return 0;
@@ -3298,6 +3291,8 @@ static void iwl3945_bg_request_scan(struct work_struct *data)
 
 	mutex_lock(&priv->mutex);
 
+	cancel_delayed_work(&priv->scan_check);
+
 	if (!iwl_is_ready(priv)) {
 		IWL_WARN(priv, "request scan called when driver not ready.\n");
 		goto done;