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: Miles Lane <miles.lane@gmail.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Acked-by: Zhu Yi <yi.zhu@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

1 files changed, 2 insertions, 7 deletions

diff --git a/drivers/net/wireless/iwlwifi/iwl3945-base.c b/drivers/net/wireless/iwlwifi/iwl3945-base.c
index 4cce66133500..ff4d0e41d7c4 100644
--- a/drivers/net/wireless/iwlwifi/iwl3945-base.c
+++ b/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;