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From: Mohammed Shafi Shajakhan <mohammed@qca.qualcomm.com>
To: "John W. Linville" <linville@tuxdriver.com>,
	Johannes Berg <johannes@sipsolutions.net>
CC: <linux-wireless@vger.kernel.org>,
	Mohammed Shafi Shajakhan <mohammed@qca.qualcomm.com>,
	<stable@vger.kernel.org>, Gary Morain <gmorain@google.com>,
	Paul Stewart <pstew@google.com>,
	Abhijit Pradhan <abhijit@qca.qualcomm.com>,
	Vasanthakumar Thiagarajan <vthiagar@qca.qualcomm.com>,
	Rajkumar Manoharan <rmanohar@qca.qualcomm.com>
Subject: [RFC] mac80211: Fix a rwlock bad magic bug
Date: Thu, 9 Feb 2012 18:34:03 +0530
Message-ID: <1328792643-6734-1-git-send-email-mohammed@qca.qualcomm.com> (sfid-20120209_140428_886744_1B43F76F)
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From: Mohammed Shafi Shajakhan <mohammed@qca.qualcomm.com>

read_lock(&tpt_trig->trig.leddev_list_lock) is accessed via the path
ieee80211_open (->) ieee80211_do_open (->) ieee80211_mod_tpt_led_trig
(->) ieee80211_start_tpt_led_trig (->) tpt_trig_timer before initializing
it.
the intilization of this read/write lock happens via the path
ieee80211_led_init (->) led_trigger_register, but we are doing
'ieee80211_led_init'  after 'ieeee80211_if_add' where we
register netdev_ops.
so we access leddev_list_lock before initializing it and causes the
following bug in chrome laptops with AR928X cards with the following
script

while true
do
sudo modprobe -v ath9k
sleep 3
sudo modprobe -r ath9k
sleep 3
done

	BUG: rwlock bad magic on CPU#1, wpa_supplicant/358, f5b9eccc
	Pid: 358, comm: wpa_supplicant Not tainted 3.0.13 #1
	Call Trace:

	[<8137b9df>] rwlock_bug+0x3d/0x47
	[<81179830>] do_raw_read_lock+0x19/0x29
	[<8137f063>] _raw_read_lock+0xd/0xf
	[<f9081957>] tpt_trig_timer+0xc3/0x145 [mac80211]
	[<f9081f3a>] ieee80211_mod_tpt_led_trig+0x152/0x174 [mac80211]
	[<f9076a3f>] ieee80211_do_open+0x11e/0x42e [mac80211]
	[<f9075390>] ? ieee80211_check_concurrent_iface+0x26/0x13c [mac80211]
	[<f9076d97>] ieee80211_open+0x48/0x4c [mac80211]
	[<812dbed8>] __dev_open+0x82/0xab
	[<812dc0c9>] __dev_change_flags+0x9c/0x113
	[<812dc1ae>] dev_change_flags+0x18/0x44
	[<8132144f>] devinet_ioctl+0x243/0x51a
	[<81321ba9>] inet_ioctl+0x93/0xac
	[<812cc951>] sock_ioctl+0x1c6/0x1ea
	[<812cc78b>] ? might_fault+0x20/0x20
	[<810b1ebb>] do_vfs_ioctl+0x46e/0x4a2
	[<810a6ebb>] ? fget_light+0x2f/0x70
	[<812ce549>] ? sys_recvmsg+0x3e/0x48
	[<810b1f35>] sys_ioctl+0x46/0x69
	[<8137fa77>] sysenter_do_call+0x12/0x2

Cc: <stable@vger.kernel.org>
Cc: Gary Morain <gmorain@google.com>
Cc: Paul Stewart <pstew@google.com>
Cc: Abhijit Pradhan <abhijit@qca.qualcomm.com>
Cc: Vasanthakumar Thiagarajan <vthiagar@qca.qualcomm.com>
Cc: Rajkumar Manoharan <rmanohar@qca.qualcomm.com>
Tested-by: Mohammed Shafi Shajakhan <mohammed@qca.qualcomm.com>
Signed-off-by: Mohammed Shafi Shajakhan <mohammed@qca.qualcomm.com>
---
 net/mac80211/main.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/mac80211/main.c b/net/mac80211/main.c
index 831a5bd..2306d75 100644
--- a/net/mac80211/main.c
+++ b/net/mac80211/main.c
@@ -909,6 +909,8 @@ int ieee80211_register_hw(struct ieee80211_hw *hw)
 		wiphy_debug(local->hw.wiphy, "Failed to initialize wep: %d\n",
 			    result);
 
+	ieee80211_led_init(local);
+
 	rtnl_lock();
 
 	result = ieee80211_init_rate_ctrl_alg(local,
@@ -930,8 +932,6 @@ int ieee80211_register_hw(struct ieee80211_hw *hw)
 
 	rtnl_unlock();
 
-	ieee80211_led_init(local);
-
 	local->network_latency_notifier.notifier_call =
 		ieee80211_max_network_latency;
 	result = pm_qos_add_notifier(PM_QOS_NETWORK_LATENCY,
-- 
1.7.0.4