ALSA: usb-audio: Don't resubmit pending URBs at MIDI error recovery

In snd_usbmidi_error_timer(), the driver tries to resubmit MIDI input
URBs to reactivate the MIDI stream, but this causes the error when
some of URBs are still pending like:

 WARNING: CPU: 0 PID: 0 at ../drivers/usb/core/urb.c:339 usb_submit_urb+0x5f/0x70()
 URB ef705c40 submitted while active
 CPU: 0 PID: 0 Comm: swapper/0 Not tainted 3.16.6-2-desktop #1
 Hardware name: FOXCONN TPS01/TPS01, BIOS 080015  03/23/2010
  c0984bfa f4009ed4 c078deaf f4009ee4 c024c884 c09a135c f4009f00 00000000
  c0984bfa 00000153 c061ac4f c061ac4f 00000009 00000001 ef705c40 e854d1c0
  f4009eec c024c8d3 00000009 f4009ee4 c09a135c f4009f00 f4009f04 c061ac4f
 Call Trace:
  [<c0205df6>] try_stack_unwind+0x156/0x170
  [<c020482a>] dump_trace+0x5a/0x1b0
  [<c0205e56>] show_trace_log_lvl+0x46/0x50
  [<c02049d1>] show_stack_log_lvl+0x51/0xe0
  [<c0205eb7>] show_stack+0x27/0x50
  [<c078deaf>] dump_stack+0x45/0x65
  [<c024c884>] warn_slowpath_common+0x84/0xa0
  [<c024c8d3>] warn_slowpath_fmt+0x33/0x40
  [<c061ac4f>] usb_submit_urb+0x5f/0x70
  [<f7974104>] snd_usbmidi_submit_urb+0x14/0x60 [snd_usbmidi_lib]
  [<f797483a>] snd_usbmidi_error_timer+0x6a/0xa0 [snd_usbmidi_lib]
  [<c02570c0>] call_timer_fn+0x30/0x130
  [<c0257442>] run_timer_softirq+0x1c2/0x260
  [<c0251493>] __do_softirq+0xc3/0x270
  [<c0204732>] do_softirq_own_stack+0x22/0x30
  [<c025186d>] irq_exit+0x8d/0xa0
  [<c0795228>] smp_apic_timer_interrupt+0x38/0x50
  [<c0794a3c>] apic_timer_interrupt+0x34/0x3c
  [<c0673d9e>] cpuidle_enter_state+0x3e/0xd0
  [<c028bb8d>] cpu_idle_loop+0x29d/0x3e0
  [<c028bd23>] cpu_startup_entry+0x53/0x60
  [<c0bfac1e>] start_kernel+0x415/0x41a

For avoiding these errors, check the pending URBs and skip
resubmitting such ones.
Reported-and-tested-by: Stefan Seyfried <stefan.seyfried@googlemail.com>
Acked-by: Clemens Ladisch <clemens@ladisch.de>
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/usb/midi.c

@@ -365,6 +365,8 @@ static void snd_usbmidi_error_timer(unsigned long data)
 		if (in && in->error_resubmit) {
 			in->error_resubmit = 0;
 			for (j = 0; j < INPUT_URBS; ++j) {
+				if (atomic_read(&in->urbs[j]->use_count))
+					continue;
 				in->urbs[j]->dev = umidi->dev;
 				snd_usbmidi_submit_urb(in->urbs[j], GFP_ATOMIC);
 			}