[RFC] mac80211: Fix possible race between sta_unblock and network softirq

* [RFC] mac80211: Fix possible race between sta_unblock and network softirq
@ 2012-01-16 15:42 Helmut Schaa
  2012-01-16 16:51 ` Johannes Berg
  0 siblings, 1 reply; 5+ messages in thread
From: Helmut Schaa @ 2012-01-16 15:42 UTC (permalink / raw)
  To: linux-wireless; +Cc: johannes, Helmut Schaa


Signed-off-by: Helmut Schaa <helmut.schaa@googlemail.com>
---

I'm currently writing some code for rt2800 that requires the driver
to stop sending to a specific station for a short period of time
(until all AMPDUs are finished to work around a hw issue that affects
rate sampling with minstrel_ht). I decided to give
ieee80211_sta_block_awake a try, however, the machine sometimes locked
up while running some performance tests but due to a hw watchdog I
wasn't able to get any sort of backtrace :(

So, while doing some review of the ieee80211_sta_block_awake I came
across this and wondered if softirqs should be disabled when delivering
the buffered frames in sta_unblock.

Using this patch I cannot reproduce the lockup anymore.

So, is there any special reason this single code path in sta_unblock
doesn't disable softirqs?

Thanks,
Helmut

 net/mac80211/sta_info.c |    6 ++++--
 1 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/net/mac80211/sta_info.c b/net/mac80211/sta_info.c
index 24d321f..5b4ab21 100644
--- a/net/mac80211/sta_info.c
+++ b/net/mac80211/sta_info.c
@@ -238,9 +238,11 @@ static void sta_unblock(struct work_struct *wk)
 	if (sta->dead)
 		return;
 
-	if (!test_sta_flag(sta, WLAN_STA_PS_STA))
+	if (!test_sta_flag(sta, WLAN_STA_PS_STA)) {
+		local_bh_disable();
 		ieee80211_sta_ps_deliver_wakeup(sta);
-	else if (test_and_clear_sta_flag(sta, WLAN_STA_PSPOLL)) {
+		local_bh_enable();
+	} else if (test_and_clear_sta_flag(sta, WLAN_STA_PSPOLL)) {
 		clear_sta_flag(sta, WLAN_STA_PS_DRIVER);
 
 		local_bh_disable();
-- 
1.7.7


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