[PATCH] mac80211: fix deferred hardware scan requests

[Chase Douglas]

From: Johannes Berg <johannes at sipsolutions.net>

Reinette found the reason for the warnings that
happened occasionally when a hw-offloaded scan
finished; her description of the problem:

  mac80211 will defer the handling of scan requests if it is
  busy with management work at the time. The scan requests
  are deferred and run after the work has completed. When
  this occurs there are currently two problems.

  * The scan request for hardware scan is not fully populated
    with the band and channels to scan not initialized.

  * When the scan is queued the state is not correctly updated
    to reflect that a scan is in progress. The problem here is
    that when the driver completes the scan and calls
    ieee80211_scan_completed() a warning will be triggered
    since mac80211 was not aware that a scan was in progress.

The reason is that the queued scan work will start
the hw scan right away when the hw_scan_req struct
has already been allocated. However, in the first
pass it will not have been filled, which happens
at the same time as setting the bits. To fix this,
simply move the allocation after the pending work
test as well, so that the first iteration of the
scan work will call __ieee80211_start_scan() even
in the hardware scan case.

Bug-identified-by: Reinette Chatre <reinette.chatre at intel.com>
Signed-off-by: Johannes Berg <johannes at sipsolutions.net>
Signed-off-by: John W. Linville <linville at tuxdriver.com>
(cherry picked from commit c0ce77b8323c1a0d4eeef97caf16c0ea971222a9)

BugLink: http://bugs.launchpad.net/bugs/528688

Signed-off-by: Chase Douglas <chase.douglas at canonical.com>
---
 net/mac80211/scan.c |   18 ++++++++++--------
 1 files changed, 10 insertions(+), 8 deletions(-)

diff --git a/net/mac80211/scan.c b/net/mac80211/scan.c
index 1a41909..fd6411d 100644
--- a/net/mac80211/scan.c
+++ b/net/mac80211/scan.c
@@ -408,6 +408,16 @@ static int __ieee80211_start_scan(struct ieee80211_sub_if_data *sdata,
 	if (local->scan_req)
 		return -EBUSY;
 
+	if (req != local->int_scan_req &&
+	    sdata->vif.type == NL80211_IFTYPE_STATION &&
+	    !list_empty(&ifmgd->work_list)) {
+		/* actually wait for the work it's doing to finish/time out */
+		set_bit(IEEE80211_STA_REQ_SCAN, &ifmgd->request);
+		local->scan_req = req;
+		local->scan_sdata = sdata;
+		return 0;
+	}
+
 	if (local->ops->hw_scan) {
 		u8 *ies;
 		int ielen;
@@ -428,14 +438,6 @@ static int __ieee80211_start_scan(struct ieee80211_sub_if_data *sdata,
 	local->scan_req = req;
 	local->scan_sdata = sdata;
 
-	if (req != local->int_scan_req &&
-	    sdata->vif.type == NL80211_IFTYPE_STATION &&
-	    !list_empty(&ifmgd->work_list)) {
-		/* actually wait for the work it's doing to finish/time out */
-		set_bit(IEEE80211_STA_REQ_SCAN, &ifmgd->request);
-		return 0;
-	}
-
 	if (local->ops->hw_scan)
 		__set_bit(SCAN_HW_SCANNING, &local->scanning);
 	else
-- 
1.6.3.3