mac80211: keep lock when calling __ieee80211_scan_completed()

We are taking local->mtx inside __ieee80211_scan_completed(), but just
before call to that function we drop the lock. Dropping/taking lock is not
good, because can lead to hard to understand race conditions.

Patch split scan_completed() code into two functions, first must be called
with local->mtx taken and second without it.

Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com>
Acked-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

1 files changed, 39 insertions, 36 deletions

diff --git a/net/mac80211/scan.c b/net/mac80211/scan.c
index 830c02bc398a..6964a4598176 100644
--- a/net/mac80211/scan.c
+++ b/net/mac80211/scan.c
@@ -249,12 +249,12 @@ static bool ieee80211_prep_hw_scan(struct ieee80211_local *local)
         return true;
 }
 
-static void __ieee80211_scan_completed(struct ieee80211_hw *hw, bool aborted)
+static bool __ieee80211_scan_completed(struct ieee80211_hw *hw, bool aborted,
+                                       bool was_hw_scan)
 {
         struct ieee80211_local *local = hw_to_local(hw);
-        bool was_hw_scan;
 
-        mutex_lock(&local->mtx);
+        lockdep_assert_held(&local->mtx);
 
         /*
          * It's ok to abort a not-yet-running scan (that
@@ -265,17 +265,13 @@ static void __ieee80211_scan_completed(struct ieee80211_hw *hw, bool aborted)
         if (WARN_ON(!local->scanning && !aborted))
                 aborted = true;
 
-        if (WARN_ON(!local->scan_req)) {
-                mutex_unlock(&local->mtx);
-                return;
-        }
+        if (WARN_ON(!local->scan_req))
+                return false;
 
-        was_hw_scan = test_bit(SCAN_HW_SCANNING, &local->scanning);
         if (was_hw_scan && !aborted && ieee80211_prep_hw_scan(local)) {
                 ieee80211_queue_delayed_work(&local->hw,
                                              &local->scan_work, 0);
-                mutex_unlock(&local->mtx);
-                return;
+                return false;
         }
 
         kfree(local->hw_scan_req);
@@ -289,23 +285,25 @@ static void __ieee80211_scan_completed(struct ieee80211_hw *hw, bool aborted)
         local->scanning = 0;
         local->scan_channel = NULL;
 
-        /* we only have to protect scan_req and hw/sw scan */
-        mutex_unlock(&local->mtx);
-
-        ieee80211_hw_config(local, IEEE80211_CONF_CHANGE_CHANNEL);
-        if (was_hw_scan)
-                goto done;
-
-        ieee80211_configure_filter(local);
+        return true;
+}
 
-        drv_sw_scan_complete(local);
+static void __ieee80211_scan_completed_finish(struct ieee80211_hw *hw,
+                                              bool was_hw_scan)
+{
+        struct ieee80211_local *local = hw_to_local(hw);
 
-        ieee80211_offchannel_return(local, true);
+        ieee80211_hw_config(local, IEEE80211_CONF_CHANGE_CHANNEL);
+        if (!was_hw_scan) {
+                ieee80211_configure_filter(local);
+                drv_sw_scan_complete(local);
+                ieee80211_offchannel_return(local, true);
+        }
 
- done:
         mutex_lock(&local->mtx);
         ieee80211_recalc_idle(local);
         mutex_unlock(&local->mtx);
+
         ieee80211_mlme_notify_scan_completed(local);
         ieee80211_ibss_notify_scan_completed(local);
         ieee80211_mesh_notify_scan_completed(local);
@@ -366,6 +364,8 @@ static int __ieee80211_start_scan(struct ieee80211_sub_if_data *sdata,
         struct ieee80211_local *local = sdata->local;
         int rc;
 
+        lockdep_assert_held(&local->mtx);
+
         if (local->scan_req)
                 return -EBUSY;
 
@@ -447,8 +447,8 @@ ieee80211_scan_get_channel_time(struct ieee80211_channel *chan)
         return IEEE80211_PROBE_DELAY + IEEE80211_CHANNEL_TIME;
 }
 
-static int ieee80211_scan_state_decision(struct ieee80211_local *local,
-                                         unsigned long *next_delay)
+static void ieee80211_scan_state_decision(struct ieee80211_local *local,
+                                          unsigned long *next_delay)
 {
         bool associated = false;
         bool tx_empty = true;
@@ -458,12 +458,6 @@ static int ieee80211_scan_state_decision(struct ieee80211_local *local,
         struct ieee80211_sub_if_data *sdata;
         struct ieee80211_channel *next_chan;
 
-        /* if no more bands/channels left, complete scan and advance to the idle state */
-        if (local->scan_channel_idx >= local->scan_req->n_channels) {
-                __ieee80211_scan_completed(&local->hw, false);
-                return 1;
-        }
-
         /*
          * check if at least one STA interface is associated,
          * check if at least one STA interface has pending tx frames
@@ -535,7 +529,6 @@ static int ieee80211_scan_state_decision(struct ieee80211_local *local,
         }
 
         *next_delay = 0;
-        return 0;
 }
 
 static void ieee80211_scan_state_leave_oper_channel(struct ieee80211_local *local,
@@ -651,7 +644,7 @@ void ieee80211_scan_work(struct work_struct *work)
                 container_of(work, struct ieee80211_local, scan_work.work);
         struct ieee80211_sub_if_data *sdata = local->scan_sdata;
         unsigned long next_delay = 0;
-        bool aborted;
+        bool aborted, hw_scan, finish;
 
         mutex_lock(&local->mtx);
 
@@ -704,8 +697,12 @@ void ieee80211_scan_work(struct work_struct *work)
         do {
                 switch (local->next_scan_state) {
                 case SCAN_DECISION:
-                        if (ieee80211_scan_state_decision(local, &next_delay))
-                                return;
+                        /* if no more bands/channels left, complete scan */
+                        if (local->scan_channel_idx >= local->scan_req->n_channels) {
+                                aborted = false;
+                                goto out_complete;
+                        }
+                        ieee80211_scan_state_decision(local, &next_delay);
                         break;
                 case SCAN_SET_CHANNEL:
                         ieee80211_scan_state_set_channel(local, &next_delay);
@@ -726,8 +723,11 @@ void ieee80211_scan_work(struct work_struct *work)
         return;
 
 out_complete:
+        hw_scan = test_bit(SCAN_HW_SCANNING, &local->scanning);
+        finish = __ieee80211_scan_completed(&local->hw, aborted, hw_scan);
         mutex_unlock(&local->mtx);
-        __ieee80211_scan_completed(&local->hw, aborted);
+        if (finish)
+                __ieee80211_scan_completed_finish(&local->hw, hw_scan);
         return;
 
 out:
@@ -796,6 +796,7 @@ int ieee80211_request_internal_scan(struct ieee80211_sub_if_data *sdata,
 void ieee80211_scan_cancel(struct ieee80211_local *local)
 {
         bool abortscan;
+        bool finish = false;
 
         cancel_delayed_work_sync(&local->scan_work);
 
@@ -806,8 +807,10 @@ void ieee80211_scan_cancel(struct ieee80211_local *local)
         mutex_lock(&local->mtx);
         abortscan = test_bit(SCAN_SW_SCANNING, &local->scanning) ||
                     (!local->scanning && local->scan_req);
+        if (abortscan)
+                finish = __ieee80211_scan_completed(&local->hw, true, false);
         mutex_unlock(&local->mtx);
 
-        if (abortscan)
-                __ieee80211_scan_completed(&local->hw, true);
+        if (finish)
+                __ieee80211_scan_completed_finish(&local->hw, false);
 }