ath9k-htc: fix lockdep warning and kernel warning after unplugging ar9271 usb device

This patch fixes two warnings below after unplugging ar9271 usb device:
	-one is a kernel warning[1]
	-another is a lockdep warning[2]

The root reason is that __skb_queue_purge can't be executed in hardirq
context, so the patch forks ath9k_skb_queue_purge(ath9k version of _skb_queue_purge),
which frees skb with dev_kfree_skb_any which can be run in hardirq
context safely, then prevent the lockdep warning and kernel warning after
unplugging ar9271 usb device.

[1] kernel warning
[  602.894005] ------------[ cut here ]------------
[  602.894005] WARNING: at net/core/skbuff.c:398 skb_release_head_state+0x71/0x87()
[  602.894005] Hardware name: 6475EK2
[  602.894005] Modules linked in: ath9k_htc ath9k ath9k_common ath9k_hw ath bridge stp llc sunrpc ipv6 cpufreq_ondemand acpi_cpufreq freq_table kvm_intel kvm arc4 ecb mac80211 snd_hda_codec_conexant snd_hda_intel snd_hda_codec snd_hwdep thinkpad_acpi snd_pcm snd_timer hwmon iTCO_wdt snd e1000e pcspkr i2c_i801 usbhid iTCO_vendor_support wmi cfg80211 yenta_socket rsrc_nonstatic pata_acpi snd_page_alloc soundcore uhci_hcd ohci_hcd ehci_hcd usbcore i915 drm_kms_helper drm i2c_algo_bit i2c_core video output [last unloaded: ath]
[  602.894005] Pid: 2506, comm: ping Tainted: G        W  2.6.34-rc3-wl #20
[  602.894005] Call Trace:
[  602.894005]  <IRQ>  [<ffffffff8104a41c>] warn_slowpath_common+0x7c/0x94
[  602.894005]  [<ffffffffa022f398>] ? __skb_queue_purge+0x43/0x4a [ath9k_htc]
[  602.894005]  [<ffffffff8104a448>] warn_slowpath_null+0x14/0x16
[  602.894005]  [<ffffffff813269c1>] skb_release_head_state+0x71/0x87
[  602.894005]  [<ffffffff8132829a>] __kfree_skb+0x16/0x81
[  602.894005]  [<ffffffff813283b2>] kfree_skb+0x7e/0x86
[  602.894005]  [<ffffffffa022f398>] __skb_queue_purge+0x43/0x4a [ath9k_htc]
[  602.894005]  [<ffffffffa022f560>] __hif_usb_tx+0x1c1/0x21b [ath9k_htc]
[  602.894005]  [<ffffffffa022f73c>] hif_usb_tx_cb+0x12f/0x154 [ath9k_htc]
[  602.894005]  [<ffffffffa00d2fbe>] usb_hcd_giveback_urb+0x91/0xc5 [usbcore]
[  602.894005]  [<ffffffffa00f6c34>] ehci_urb_done+0x7a/0x8b [ehci_hcd]
[  602.894005]  [<ffffffffa00f6f33>] qh_completions+0x2ee/0x376 [ehci_hcd]
[  602.894005]  [<ffffffffa00f8ba5>] ehci_work+0x95/0x76e [ehci_hcd]
[  602.894005]  [<ffffffffa00fa5ae>] ? ehci_irq+0x2f/0x1d4 [ehci_hcd]
[  602.894005]  [<ffffffffa00fa725>] ehci_irq+0x1a6/0x1d4 [ehci_hcd]
[  602.894005]  [<ffffffff810a6d18>] ? __rcu_process_callbacks+0x7a/0x2df
[  602.894005]  [<ffffffff810a47a4>] ? handle_fasteoi_irq+0x22/0xd2
[  602.894005]  [<ffffffffa00d268d>] usb_hcd_irq+0x4a/0xa7 [usbcore]
[  602.894005]  [<ffffffff810a2853>] handle_IRQ_event+0x77/0x14f
[  602.894005]  [<ffffffff813285ce>] ? skb_release_data+0xc9/0xce
[  602.894005]  [<ffffffff810a4814>] handle_fasteoi_irq+0x92/0xd2
[  602.894005]  [<ffffffff8100c4fb>] handle_irq+0x88/0x91
[  602.894005]  [<ffffffff8100baed>] do_IRQ+0x63/0xc9
[  602.894005]  [<ffffffff81354245>] ? ip_flush_pending_frames+0x4d/0x5c
[  602.894005]  [<ffffffff813ba993>] ret_from_intr+0x0/0x16
[  602.894005]  <EOI>  [<ffffffff811095fe>] ? __delete_object+0x5a/0xb1
[  602.894005]  [<ffffffff813ba5f5>] ? _raw_write_unlock_irqrestore+0x47/0x7e
[  602.894005]  [<ffffffff813ba5fa>] ? _raw_write_unlock_irqrestore+0x4c/0x7e
[  602.894005]  [<ffffffff811095fe>] __delete_object+0x5a/0xb1
[  602.894005]  [<ffffffff81109814>] delete_object_full+0x25/0x31
[  602.894005]  [<ffffffff813a60c0>] kmemleak_free+0x26/0x45
[  602.894005]  [<ffffffff810ff517>] kfree+0xaa/0x149
[  602.894005]  [<ffffffff81323fb7>] ? sock_def_write_space+0x84/0x89
[  602.894005]  [<ffffffff81354245>] ? ip_flush_pending_frames+0x4d/0x5c
[  602.894005]  [<ffffffff813285ce>] skb_release_data+0xc9/0xce
[  602.894005]  [<ffffffff813282a2>] __kfree_skb+0x1e/0x81
[  602.894005]  [<ffffffff813283b2>] kfree_skb+0x7e/0x86
[  602.894005]  [<ffffffff81354245>] ip_flush_pending_frames+0x4d/0x5c
[  602.894005]  [<ffffffff81370c1f>] raw_sendmsg+0x653/0x709
[  602.894005]  [<ffffffff81379e31>] inet_sendmsg+0x54/0x5d
[  602.894005]  [<ffffffff813207a2>] ? sock_recvmsg+0xc6/0xdf
[  602.894005]  [<ffffffff813208c1>] sock_sendmsg+0xc0/0xd9
[  602.894005]  [<ffffffff810e13b4>] ? might_fault+0x68/0xb8
[  602.894005]  [<ffffffff810e13fd>] ? might_fault+0xb1/0xb8
[  602.894005]  [<ffffffff8132a1c3>] ? copy_from_user+0x2f/0x31
[  602.894005]  [<ffffffff8132a5b3>] ? verify_iovec+0x54/0x91
[  602.894005]  [<ffffffff81320d41>] sys_sendmsg+0x1da/0x241
[  602.894005]  [<ffffffff8103d327>] ? finish_task_switch+0x0/0xc9
[  602.894005]  [<ffffffff8103d327>] ? finish_task_switch+0x0/0xc9
[  602.894005]  [<ffffffff8107642e>] ? trace_hardirqs_on_caller+0x16/0x150
[  602.894005]  [<ffffffff813ba27d>] ? _raw_spin_unlock_irq+0x56/0x63
[  602.894005]  [<ffffffff8103d3cb>] ? finish_task_switch+0xa4/0xc9
[  602.894005]  [<ffffffff8103d327>] ? finish_task_switch+0x0/0xc9
[  602.894005]  [<ffffffff810357fe>] ? need_resched+0x23/0x2d
[  602.894005]  [<ffffffff8107642e>] ? trace_hardirqs_on_caller+0x16/0x150
[  602.894005]  [<ffffffff813b9750>] ? trace_hardirqs_on_thunk+0x3a/0x3f
[  602.894005]  [<ffffffff81009c02>] system_call_fastpath+0x16/0x1b
[  602.894005] ---[ end trace 91ba2d8dc7826839 ]---

[2] lockdep warning
[  169.363215] ======================================================
[  169.365390] [ INFO: HARDIRQ-safe -> HARDIRQ-unsafe lock order detected ]
[  169.366334] 2.6.34-rc3-wl #20
[  169.366872] ------------------------------------------------------
[  169.366872] khubd/78 [HC0[0]:SC0[0]:HE0:SE1] is trying to acquire:
[  169.366872]  (clock-AF_INET){++.?..}, at: [<ffffffff81323f51>] sock_def_write_space+0x1e/0x89
[  169.366872]
[  169.366872] and this task is already holding:
[  169.366872]  (&(&hif_dev->tx.tx_lock)->rlock){-.-...}, at: [<ffffffffa03715b0>] hif_usb_stop+0x24/0x53 [ath9k_htc]
[  169.366872] which would create a new lock dependency:
[  169.366872]  (&(&hif_dev->tx.tx_lock)->rlock){-.-...} -> (clock-AF_INET){++.?..}
[  169.366872]
[  169.366872] but this new dependency connects a HARDIRQ-irq-safe lock:
[  169.366872]  (&(&hif_dev->tx.tx_lock)->rlock){-.-...}
[  169.366872] ... which became HARDIRQ-irq-safe at:
[  169.366872]   [<ffffffff810772d5>] __lock_acquire+0x2c6/0xd2b
[  169.366872]   [<ffffffff8107866d>] lock_acquire+0xec/0x119
[  169.366872]   [<ffffffff813b99bb>] _raw_spin_lock+0x40/0x73
[  169.366872]   [<ffffffffa037163d>] hif_usb_tx_cb+0x5e/0x154 [ath9k_htc]
[  169.366872]   [<ffffffffa00d2fbe>] usb_hcd_giveback_urb+0x91/0xc5 [usbcore]
[  169.366872]   [<ffffffffa00f6c34>] ehci_urb_done+0x7a/0x8b [ehci_hcd]
[  169.366872]   [<ffffffffa00f6f33>] qh_completions+0x2ee/0x376 [ehci_hcd]
[  169.366872]   [<ffffffffa00f8ba5>] ehci_work+0x95/0x76e [ehci_hcd]
[  169.366872]   [<ffffffffa00fa725>] ehci_irq+0x1a6/0x1d4 [ehci_hcd]
[  169.366872]   [<ffffffffa00d268d>] usb_hcd_irq+0x4a/0xa7 [usbcore]
[  169.366872]   [<ffffffff810a2853>] handle_IRQ_event+0x77/0x14f
[  169.366872]   [<ffffffff810a4814>] handle_fasteoi_irq+0x92/0xd2
[  169.366872]   [<ffffffff8100c4fb>] handle_irq+0x88/0x91
[  169.366872]   [<ffffffff8100baed>] do_IRQ+0x63/0xc9
[  169.366872]   [<ffffffff813ba993>] ret_from_intr+0x0/0x16
[  169.366872]   [<ffffffff8130f6ee>] cpuidle_idle_call+0xa7/0x115
[  169.366872]   [<ffffffff81008c4f>] cpu_idle+0x68/0xc4
[  169.366872]   [<ffffffff813a41e0>] rest_init+0x104/0x10b
[  169.366872]   [<ffffffff81899db3>] start_kernel+0x3f1/0x3fc
[  169.366872]   [<ffffffff818992c8>] x86_64_start_reservations+0xb3/0xb7
[  169.366872]   [<ffffffff818993c4>] x86_64_start_kernel+0xf8/0x107
[  169.366872]
[  169.366872] to a HARDIRQ-irq-unsafe lock:
[  169.366872]  (clock-AF_INET){++.?..}
[  169.366872] ... which became HARDIRQ-irq-unsafe at:
[  169.366872] ...  [<ffffffff81077349>] __lock_acquire+0x33a/0xd2b
[  169.366872]   [<ffffffff8107866d>] lock_acquire+0xec/0x119
[  169.366872]   [<ffffffff813b9d07>] _raw_write_lock_bh+0x45/0x7a
[  169.366872]   [<ffffffff8135cf14>] tcp_close+0x165/0x34d
[  169.366872]   [<ffffffff8137aced>] inet_release+0x55/0x5c
[  169.366872]   [<ffffffff81321350>] sock_release+0x1f/0x6e
[  169.366872]   [<ffffffff813213c6>] sock_close+0x27/0x2b
[  169.366872]   [<ffffffff8110dd45>] __fput+0x125/0x1ca
[  169.366872]   [<ffffffff8110de04>] fput+0x1a/0x1c
[  169.366872]   [<ffffffff8110adc9>] filp_close+0x68/0x72
[  169.366872]   [<ffffffff8110ae80>] sys_close+0xad/0xe7
[  169.366872]   [<ffffffff81009c02>] system_call_fastpath+0x16/0x1b

(Trimmed at the "other info that might help us debug this" line in
the interest of brevity... -- JWL)

Signed-off-by: Ming Lei <tom.leiming@gmail.com>
Acked-by: Sujith <Sujith.Manoharan@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/ath/ath9k/hif_usb.c

@@ -149,6 +149,13 @@ static void hif_usb_tx_cb(struct urb *urb)
 	}
 }
 
+static inline void ath9k_skb_queue_purge(struct sk_buff_head *list)
+{
+	struct sk_buff *skb;
+	while ((skb = __skb_dequeue(list)) != NULL)
+		dev_kfree_skb_any(skb);
+}
+
 /* TX lock has to be taken */
 static int __hif_usb_tx(struct hif_device_usb *hif_dev)
 {
@@ -207,7 +214,7 @@ static int __hif_usb_tx(struct hif_device_usb *hif_dev)
 	ret = usb_submit_urb(tx_buf->urb, GFP_ATOMIC);
 	if (ret) {
 		tx_buf->len = tx_buf->offset = 0;
-		__skb_queue_purge(&tx_buf->skb_queue);
+		ath9k_skb_queue_purge(&tx_buf->skb_queue);
 		__skb_queue_head_init(&tx_buf->skb_queue);
 		list_move_tail(&tx_buf->list, &hif_dev->tx.tx_buf);
 		hif_dev->tx.tx_buf_cnt++;
@@ -274,7 +281,7 @@ static void hif_usb_stop(void *hif_handle, u8 pipe_id)
 	unsigned long flags;
 
 	spin_lock_irqsave(&hif_dev->tx.tx_lock, flags);
-	__skb_queue_purge(&hif_dev->tx.tx_skb_queue);
+	ath9k_skb_queue_purge(&hif_dev->tx.tx_skb_queue);
 	hif_dev->tx.tx_skb_cnt = 0;
 	hif_dev->tx.flags |= HIF_USB_TX_STOP;
 	spin_unlock_irqrestore(&hif_dev->tx.tx_lock, flags);