At Linux v3.5, packet processing can be done in process context of ALSA
PCM application as well as software IRQ context for OHCI 1394. Below is
an example of the callgraph (some calls are omitted).

ioctl(2) with e.g. HWSYNC
(sound/core/pcm_native.c)
->snd_pcm_common_ioctl1()
  ->snd_pcm_hwsync()
    ->snd_pcm_stream_lock_irq
    (sound/core/pcm_lib.c)
    ->snd_pcm_update_hw_ptr()
      ->snd_pcm_udpate_hw_ptr0()
        ->struct snd_pcm_ops.pointer()
        (sound/firewire/*)
        = Each handler on drivers in ALSA firewire stack
          (sound/firewire/amdtp-stream.c)
          ->amdtp_stream_pcm_pointer()
            (drivers/firewire/core-iso.c)
            ->fw_iso_context_flush_completions()
              ->struct fw_card_driver.flush_iso_completion()
              (drivers/firewire/ohci.c)
              = flush_iso_completions()
                ->struct fw_iso_context.callback.sc
                (sound/firewire/amdtp-stream.c)
                = in_stream_callback() or out_stream_callback()
                  ->...
    ->snd_pcm_stream_unlock_irq

When packet queueing error occurs or detecting invalid packets in
'in_stream_callback()' or 'out_stream_callback()', 'snd_pcm_stop_xrun()'
is called on local CPU with disabled IRQ.

(sound/firewire/amdtp-stream.c)
in_stream_callback() or out_stream_callback()
->amdtp_stream_pcm_abort()
  ->snd_pcm_stop_xrun()
    ->snd_pcm_stream_lock_irqsave()
    ->snd_pcm_stop()
    ->snd_pcm_stream_unlock_irqrestore()

The process is stalled on the CPU due to attempt to acquire recursive lock.

[  562.630853] INFO: rcu_sched detected stalls on CPUs/tasks:
[  562.630861]      2-...: (1 GPs behind) idle=37d/140000000000000/0 softirq=38323/38323 fqs=7140
[  562.630862]      (detected by 3, t=15002 jiffies, g=21036, c=21035, q=5933)
[  562.630866] Task dump for CPU 2:
[  562.630867] alsa-source-OXF R  running task        0  6619      1 0x00000008
[  562.630870] Call Trace:
[  562.630876]  ? vt_console_print+0x79/0x3e0
[  562.630880]  ? msg_print_text+0x9d/0x100
[  562.630883]  ? up+0x32/0x50
[  562.630885]  ? irq_work_queue+0x8d/0xa0
[  562.630886]  ? console_unlock+0x2b6/0x4b0
[  562.630888]  ? vprintk_emit+0x312/0x4a0
[  562.630892]  ? dev_vprintk_emit+0xbf/0x230
[  562.630895]  ? do_sys_poll+0x37a/0x550
[  562.630897]  ? dev_printk_emit+0x4e/0x70
[  562.630900]  ? __dev_printk+0x3c/0x80
[  562.630903]  ? _raw_spin_lock+0x20/0x30
[  562.630909]  ? snd_pcm_stream_lock+0x31/0x50 [snd_pcm]
[  562.630914]  ? _snd_pcm_stream_lock_irqsave+0x2e/0x40 [snd_pcm]
[  562.630918]  ? snd_pcm_stop_xrun+0x16/0x70 [snd_pcm]
[  562.630922]  ? in_stream_callback+0x3e6/0x450 [snd_firewire_lib]
[  562.630925]  ? handle_ir_packet_per_buffer+0x8e/0x1a0 [firewire_ohci]
[  562.630928]  ? ohci_flush_iso_completions+0xa3/0x130 [firewire_ohci]
[  562.630932]  ? fw_iso_context_flush_completions+0x15/0x20 [firewire_core]
[  562.630935]  ? amdtp_stream_pcm_pointer+0x2d/0x40 [snd_firewire_lib]
[  562.630938]  ? pcm_capture_pointer+0x19/0x20 [snd_oxfw]
[  562.630943]  ? snd_pcm_update_hw_ptr0+0x47/0x3d0 [snd_pcm]
[  562.630945]  ? poll_select_copy_remaining+0x150/0x150
[  562.630947]  ? poll_select_copy_remaining+0x150/0x150
[  562.630952]  ? snd_pcm_update_hw_ptr+0x10/0x20 [snd_pcm]
[  562.630956]  ? snd_pcm_hwsync+0x45/0xb0 [snd_pcm]
[  562.630960]  ? snd_pcm_common_ioctl1+0x1ff/0xc90 [snd_pcm]
[  562.630962]  ? futex_wake+0x90/0x170
[  562.630966]  ? snd_pcm_capture_ioctl1+0x136/0x260 [snd_pcm]
[  562.630970]  ? snd_pcm_capture_ioctl+0x27/0x40 [snd_pcm]
[  562.630972]  ? do_vfs_ioctl+0xa3/0x610
[  562.630974]  ? vfs_read+0x11b/0x130
[  562.630976]  ? SyS_ioctl+0x79/0x90
[  562.630978]  ? entry_SYSCALL_64_fastpath+0x1e/0xad

This commit fixes the above bug. This assumes two cases:
1. Any error is detected in software IRQ context of OHCI 1394 context.
In this case, PCM substream should be aborted in packet handler. On the
other hand, it should not be done in any process context. TO distinguish
these two context, use 'in_interrupt()' macro.
2. Any error is detect in process context of ALSA PCM application.
In this case, PCM substream should not be aborted in packet handler
because PCM substream lock is acquired. The task to abort PCM substream
should be done in ALSA PCM core. For this purpose, SNDRV_PCM_POS_XRUN is
returned at 'struct snd_pcm_ops.pointer()'.
Suggested-by: Clemens Ladisch <clemens@ladisch.de>
Fixes: e9148ddd("ALSA: firewire-lib: flush completed packets when reading PCM position")
Cc: <stable@vger.kernel.org> # 4.9+
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>