usb: storage: fix lockdep warning inside usb_stor_pre_reset(v2)

This patch fixes one lockdep warning[1] inside usb_stor_pre_reset.

If the current configuration includes multiple mass storage interfaces,
the 'AA' lockdep warning will be triggered since the lock class of
'us->dev_mutex' is acquired two times in .reset path. It isn't
a real deadlock, so just take the lockdep_set_class annotation to
remove the warning.

[1], lockdep warning log
:[ INFO: possible recursive locking detected ]
:3.3.0-0.rc5.git3.1.fc17.x86_64 #1 Tainted: G        W
:---------------------------------------------
:usb-storage/14846 is trying to acquire lock:
: (&(us->dev_mutex)){+.+.+.}, at: [<ffffffffa0481c0c>] usb_stor_pre_reset+0x1c/0x20 [usb_storage]
:but task is already holding lock:
: (&(us->dev_mutex)){+.+.+.}, at: [<ffffffffa0481c0c>] usb_stor_pre_reset+0x1c/0x20 [usb_storage]
:other info that might help us debug this:
: Possible unsafe locking scenario:
:       CPU0
:       ----
:  lock(&(us->dev_mutex));
:  lock(&(us->dev_mutex));
: *** DEADLOCK ***
: May be due to missing lock nesting notation
:2 locks held by usb-storage/14846:
: #0:  (&__lockdep_no_validate__){......}, at: [<ffffffff8147e6a5>] usb_lock_device_for_reset+0x95/0x100
: #1:  (&(us->dev_mutex)){+.+.+.}, at: [<ffffffffa0481c0c>] usb_stor_pre_reset+0x1c/0x20 [usb_storage]
:stack backtrace:
:Pid: 14846, comm: usb-storage Tainted: G        W 3.3.0-0.rc5.git3.1.fc17.x86_64 #1
:Call Trace:
: [<ffffffff810cbdaf>] __lock_acquire+0x168f/0x1bb0
: [<ffffffff81021083>] ? native_sched_clock+0x13/0x80
: [<ffffffff810210f9>] ? sched_clock+0x9/0x10
: [<ffffffff810210f9>] ? sched_clock+0x9/0x10
: [<ffffffff810a2975>] ? sched_clock_local+0x25/0xa0
: [<ffffffff810cc9a1>] lock_acquire+0xa1/0x1e0
: [<ffffffffa0481c0c>] ? usb_stor_pre_reset+0x1c/0x20 [usb_storage]
: [<ffffffff81699c86>] mutex_lock_nested+0x76/0x3a0
: [<ffffffffa0481c0c>] ? usb_stor_pre_reset+0x1c/0x20 [usb_storage]
: [<ffffffffa0481c0c>] ? usb_stor_pre_reset+0x1c/0x20 [usb_storage]
: [<ffffffffa0481c0c>] usb_stor_pre_reset+0x1c/0x20 [usb_storage]
: [<ffffffff8148184d>] usb_reset_device+0x7d/0x190
: [<ffffffffa048119c>] usb_stor_port_reset+0x7c/0x80 [usb_storage]
: [<ffffffffa0481234>] usb_stor_invoke_transport+0x94/0x560 [usb_storage]
: [<ffffffff810cd3b2>] ? mark_held_locks+0xb2/0x130
: [<ffffffff8169dbd0>] ? _raw_spin_unlock_irq+0x30/0x50
: [<ffffffffa047fe3e>] usb_stor_transparent_scsi_command+0xe/0x10 [usb_storage]
: [<ffffffffa0481ae3>] usb_stor_control_thread+0x173/0x280 [usb_storage]
: [<ffffffffa0481970>] ? fill_inquiry_response+0x20/0x20 [usb_storage]
: [<ffffffff8108a3f7>] kthread+0xb7/0xc0
: [<ffffffff816a7d34>] kernel_thread_helper+0x4/0x10
: [<ffffffff8169e0f4>] ? retint_restore_args+0x13/0x13
: [<ffffffff8108a340>] ? kthread_worker_fn+0x1a0/0x1a0
: [<ffffffff816a7d30>] ? gs_change+0x13/0x13
Reported-By: Dave Jones <davej@redhat.com>
Signed-off-by: Ming Lei <tom.leiming@gmail.com>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/storage/usb.c

@@ -132,6 +132,35 @@ static struct us_unusual_dev for_dynamic_ids =
 #undef COMPLIANT_DEV
 #undef USUAL_DEV
 
+#ifdef CONFIG_LOCKDEP
+
+static struct lock_class_key us_interface_key[USB_MAXINTERFACES];
+
+static void us_set_lock_class(struct mutex *mutex,
+		struct usb_interface *intf)
+{
+	struct usb_device *udev = interface_to_usbdev(intf);
+	struct usb_host_config *config = udev->actconfig;
+	int i;
+
+	for (i = 0; i < config->desc.bNumInterfaces; i++) {
+		if (config->interface[i] == intf)
+			break;
+	}
+
+	BUG_ON(i == config->desc.bNumInterfaces);
+
+	lockdep_set_class(mutex, &us_interface_key[i]);
+}
+
+#else
+
+static void us_set_lock_class(struct mutex *mutex,
+		struct usb_interface *intf)
+{
+}
+
+#endif
 
 #ifdef CONFIG_PM	/* Minimal support for suspend and resume */
 
@@ -895,6 +924,7 @@ int usb_stor_probe1(struct us_data **pus,
 	*pus = us = host_to_us(host);
 	memset(us, 0, sizeof(struct us_data));
 	mutex_init(&(us->dev_mutex));
+	us_set_lock_class(&us->dev_mutex, intf);
 	init_completion(&us->cmnd_ready);
 	init_completion(&(us->notify));
 	init_waitqueue_head(&us->delay_wait);