On Wed, 2016-11-23 at 15:59 +0800, Chris Chiu wrote:

ieee80211_iface_work() will check if sw scanning is in progress
before handling block ack session. In our case, the RTL8821AE
operate in station mode, when tx session expired, DELBA packet
stuck during sw scanning and so do other data packets.

ieee80211_scan_state_decision() will take lots of time in
SCAN_SUSPEND/SCAN_RESUME state due to !tx_empty or bad_latency.
Then the sw scanning mostly take > 20 seconds to finish or even
worse in our case RTL8821AE have 37 channels for 2G+5G to scan
and tx stalls ~300 seconds. AP side still thinks the connection
is alive because it still receives the QoS NULL packet from STA.
So the link state will never change but actually no data tx/rx
during this long time.

This commit tries to send out packet in SCAN_SUSPEND state so the
sw scanning can complete more efficiently and less affect on Block
Ack session handling. Verified on RTL8821AE for > 30000 pings and
no Tx BA session stuck observed.

The premise seems fairly reasonable, although I'm a little worried that
if so much new traffic is coming in we never finish the scan suspend?
Actually, the queues are still stopped, so it's only management frames
that can come in, so that should be ok?

+	test_and_clear_bit(SCAN_SUSPEND_SCANNING, &local->scanning);

That makes no sense, you're not checking the return value, just clear
the bit without test.
 

Why are you using the non-atomic version here, vs. the atomic one
above?

johannes