Bluetooth: Fix possible deadlock in btusb

commit 8f9d02f4 introduced spinlocks
in btusb_work. This is run in a context of a worqueue and can be interrupted
by hardware irq. If it happens while spinlock is held, we have a deadlock.
Solution is to use _irqsave/_resore version of locking

[  466.460560] =================================
[  466.460565] [ INFO: inconsistent lock state ]
[  466.460572] 4.3.0-rc6+ #1 Tainted: G        W
[  466.460576] ---------------------------------
[  466.460582] inconsistent {IN-HARDIRQ-W} -> {HARDIRQ-ON-W} usage.
[  466.460589] kworker/0:2/94 [HC0[0]:SC0[0]:HE1:SE1] takes:
[  466.460595]  (&(&data->rxlock)->rlock){?.-...}, at: [<ffffffffa0526923>] btusb_work+0xa3/0x3fd [btusb]
[  466.460621] {IN-HARDIRQ-W} state was registered at:
[  466.460625]   [<ffffffff811021b5>] __lock_acquire+0xc45/0x1e80
[  466.460638]   [<ffffffff811040d5>] lock_acquire+0xe5/0x1f0
[  466.460646]   [<ffffffff8182f108>] _raw_spin_lock+0x38/0x50
[  466.460657]   [<ffffffffa0525448>] btusb_recv_intr+0x38/0x170 [btusb]
[  466.460668]   [<ffffffffa0525626>] btusb_intr_complete+0xa6/0x130 [btusb]
[  466.460679]   [<ffffffff815d8f1e>] __usb_hcd_giveback_urb+0x8e/0x160
[  466.460690]   [<ffffffff815d911f>] usb_hcd_giveback_urb+0x3f/0x120
[  466.460698]   [<ffffffff81606e4d>] uhci_giveback_urb+0xad/0x280
[  466.460706]   [<ffffffff81608f64>] uhci_scan_schedule.part.33+0x6b4/0xbe0
[  466.460714]   [<ffffffff81609b50>] uhci_irq+0xd0/0x180
[  466.460722]   [<ffffffff815d8296>] usb_hcd_irq+0x26/0x40
[  466.460729]   [<ffffffff81117d40>] handle_irq_event_percpu+0x40/0x300
[  466.460739]   [<ffffffff81118040>] handle_irq_event+0x40/0x60
[  466.460746]   [<ffffffff8111af39>] handle_fasteoi_irq+0x89/0x150
[  466.460754]   [<ffffffff8101e0f3>] handle_irq+0x73/0x120
[  466.460763]   [<ffffffff81832f11>] do_IRQ+0x61/0x120
[  466.460772]   [<ffffffff8183084c>] ret_from_intr+0x0/0x31
[  466.460780]   [<ffffffff81697a77>] cpuidle_enter+0x17/0x20
[  466.460790]   [<ffffffff810f62c2>] call_cpuidle+0x32/0x60
[  466.460800]   [<ffffffff810f65a8>] cpu_startup_entry+0x2b8/0x3f0
[  466.460807]   [<ffffffff818214ca>] rest_init+0x13a/0x140
[  466.460817]   [<ffffffff81f76029>] start_kernel+0x4a3/0x4c4
[  466.460827]   [<ffffffff81f75339>] x86_64_start_reservations+0x2a/0x2c
[  466.460837]   [<ffffffff81f75485>] x86_64_start_kernel+0x14a/0x16d
[  466.460846] irq event stamp: 754913
[  466.460851] hardirqs last  enabled at (754913): [<ffffffff8182f4cc>] _raw_spin_unlock_irq+0x2c/0x40
[  466.460861] hardirqs last disabled at (754912): [<ffffffff8182f28d>] _raw_spin_lock_irq+0x1d/0x60
[  466.460869] softirqs last  enabled at (753024): [<ffffffff810aeaa0>] __do_softirq+0x380/0x490
[  466.460880] softirqs last disabled at (753009): [<ffffffff810aedef>] irq_exit+0x10f/0x120
[  466.460888]
               other info that might help us debug this:
[  466.460894]  Possible unsafe locking scenario:

[  466.460899]        CPU0
[  466.460903]        ----
[  466.460907]   lock(&(&data->rxlock)->rlock);
[  466.460915]   <Interrupt>
[  466.460918]     lock(&(&data->rxlock)->rlock);
[  466.460926]
                *** DEADLOCK ***

[  466.460935] 2 locks held by kworker/0:2/94:
[  466.460939]  #0:  ("events"){.+.+.+}, at: [<ffffffff810c69bb>] process_one_work+0x16b/0x660
[  466.460958]  #1:  ((&data->work)){+.+...}, at: [<ffffffff810c69bb>] process_one_work+0x16b/0x660
[  466.460974]
Signed-off-by: Kuba Pawlak <kubax.t.pawlak@intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>

drivers/bluetooth/btusb.c

@@ -1372,6 +1372,8 @@ static void btusb_work(struct work_struct *work)
 		}
 
 		if (data->isoc_altsetting != new_alts) {
+			unsigned long flags;
+
 			clear_bit(BTUSB_ISOC_RUNNING, &data->flags);
 			usb_kill_anchored_urbs(&data->isoc_anchor);
 
@@ -1384,10 +1386,10 @@ static void btusb_work(struct work_struct *work)
 			 * Clear outstanding fragment when selecting a new
 			 * alternate setting.
 			 */
-			spin_lock(&data->rxlock);
+			spin_lock_irqsave(&data->rxlock, flags);
 			kfree_skb(data->sco_skb);
 			data->sco_skb = NULL;
-			spin_unlock(&data->rxlock);
+			spin_unlock_irqrestore(&data->rxlock, flags);
 
 			if (__set_isoc_interface(hdev, new_alts) < 0)
 				return;