From 58905ca5b11a0ff3860f55b789cbbf052f7158a7 Mon Sep 17 00:00:00 2001 From: Johannes Berg Date: Thu, 7 May 2009 14:23:01 +0200 Subject: mac80211: fix scan channel race When a software scan starts, it first sets sw_scanning, but leaves the scan_channel "unset" (it currently actually gets initialised to a default). Now, when something else tries to (re)configure the hardware in the window between these two events (after sw_scanning = true, but before scan_channel is set), the current code switches to the (unset!) scan_channel. This causes trouble, especially when switching bands and sending frames on the wrong channel. To work around this, leave scan_channel initialised to NULL and use it to determine whether or not a switch to a different channel should occur (and also use the same condition to check whether to adjust power for scan or not). Additionally, avoid reconfiguring the hardware completely when recalculating idle resulted in no changes, this was the problem that originally led us to discover the race condition in the first place, which was helpfully bisected by Pavel. This part of the patch should not be necessary with the other fixes, but not calling the ieee80211_hw_config function when we know it to be unnecessary is certainly a correct thing to do. Unfortunately, this patch cannot and does not fix the race condition completely, but due to the way the scan code is structured it makes the particular problem Pavel discovered (race while changing channel at the same time as transmitting frames) go away. To fix it completely, more work especially with locking configuration is needed. Bisected-by: Pavel Roskin Signed-off-by: Johannes Berg Signed-off-by: John W. Linville --- net/mac80211/scan.c | 1 + 1 file changed, 1 insertion(+) (limited to 'net/mac80211/scan.c') diff --git a/net/mac80211/scan.c b/net/mac80211/scan.c index c99ef8d04d3d..e51b99b1473c 100644 --- a/net/mac80211/scan.c +++ b/net/mac80211/scan.c @@ -298,6 +298,7 @@ void ieee80211_scan_completed(struct ieee80211_hw *hw, bool aborted) was_hw_scan = local->hw_scanning; local->hw_scanning = false; local->sw_scanning = false; + local->scan_channel = NULL; /* we only have to protect scan_req and hw/sw scan */ mutex_unlock(&local->scan_mtx); -- cgit v1.2.1