Re: [alsa-devel] 2.6.26.[6|7]-rt11, alsa rawmidi, seq hang

Fernando Lopez-Lezcano
2008-11-07T18:14:17Z

On Fri, 2008-11-07 at 10:12 +0100, Clemens Ladisch wrote:
> Fernando Lopez-Lezcano wrote:
> > I'm seeing a realtime patch related hard hang in the kernel alsa
> > subsystem (MIDI input/output). In a nutshell:
> >
> > - alsa rawmidi works (ie: "rawmidi -v -i hw:0" outputs a stream of
> > messages when pointed to a midi capable card that has an external
> > keyboard connected).
> >
> > - the alsa sequencer interface works (ie: aplaymidi connected to
> > aseqdump transfers data just fine).
> >
> > - BOTH combined do NOT work (ie: use aconnect to connect the port that
> > corresponds to the external midi interface to aseqdump: aseqdump hangs
> > forever after transferring the first message and the only way out is a
> > reboot).
>
> Please try the snd-virmidi driver, then we'd have a test case that does
> not require MIDI hardware.
>
> > ... including the output of a "echo t >/proc/sysrq-trigger" that
> > should show where aseqdump currently hangs (or so I think).
>
> It hangs in tasklet_kill(), which gets called while it tries to close
> the rawmidi port.
>
> The rawmidi framework uses this tasklet to notify the sequencer that new
> MIDI data is available. The handler function is
> snd_rawmidi_input_event_tasklet() in sound/core/rawmidi.c; the sequencer
> callback that gets called from there is snd_midi_input_event() in
> core/seq/seq_midi.c.
>
> You say that the first event gets delivered, so it might be possible
> that the tasklet never finishes executing. Please check whether the
> call to snd_seq_kernel_client_dispatch() in snd_midi_input_event()
> ever returns.

I added a printk before and after the call, it looks like it gets called
and it returns (but only _once_... aseqdump hangs in an unkillable state
as before).

But the hang is different, I'll reboot and retry to see if it is
repeatable:

--------
Nov 7 10:05:36 host kernel: =======================
Nov 7 10:05:36 host kernel: aseqdump S [f2e5c330] f78df0f0 0
5256 5185
Nov 7 10:05:36 host kernel: f2cffbd4 00000086 f2cffb88 f78df0f0
00000003 f2e5c330 f2e5c5c4 c4847700
Nov 7 10:05:36 host kernel: 00000001 c4847700 ef1ba352 0000002c
c4844054 00000000 fffe5e91 00000246
Nov 7 10:05:36 host kernel: f57fc274 00000000 00000000 00000000
ffffffff 00000000 7fffffff f2cffe98
Nov 7 10:05:36 host kernel: Call Trace:
Nov 7 10:05:36 host kernel: [<c0643ba5>] schedule+0xbf/0xd8
Nov 7 10:05:36 host kernel: [<c0643c72>] schedule_timeout+0x17/0xbc
Nov 7 10:05:36 host kernel: [<c0496c8f>] ? __pollwait+0xad/0xb6
Nov 7 10:05:36 host kernel: [<f8971b34>] ? snd_seq_fifo_poll_wait
+0x18/0x25 [snd_seq]
Nov 7 10:05:36 host kernel: [<f896efad>] ? snd_seq_poll+0x4d/0x9f
[snd_seq]
Nov 7 10:05:36 host kernel: [<c0495d92>] do_sys_poll+0x292/0x348
Nov 7 10:05:36 host kernel: [<c0496be2>] ? __pollwait+0x0/0xb6
Nov 7 10:05:36 host kernel: [<c0425c81>] ? default_wake_function
+0x0/0x12
Nov 7 10:05:36 host kernel: [<c0645736>] ? rt_spin_lock+0x38/0x3b
Nov 7 10:05:36 host kernel: [<c04752f7>] ? page_address+0x88/0xaa
Nov 7 10:05:36 host kernel: [<c047596d>] ? kmap_high+0x421/0x42a
Nov 7 10:05:36 host kernel: [<c04ff574>] ? radix_valid_always+0x0/0xa
Nov 7 10:05:36 host kernel: [<c046430b>] ? __rcu_read_unlock+0x6d/0x72
Nov 7 10:05:36 host kernel: [<c04699ec>] ? find_get_page+0xfa/0x120
Nov 7 10:05:36 host kernel: [<c06456c1>] ? __rt_spin_lock+0x24/0x61
Nov 7 10:05:36 host kernel: [<c0645736>] ? rt_spin_lock+0x38/0x3b
Nov 7 10:05:36 host kernel: [<c0420afc>] ? __enqueue_entity+0xe3/0xeb
Nov 7 10:05:36 host kernel: [<c041f87b>] ? task_rq_lock+0x44/0x6e
Nov 7 10:05:36 host kernel: [<c0425c76>] ? try_to_wake_up+0x212/0x21d
Nov 7 10:05:36 host kernel: [<c0425c91>] ? default_wake_function
+0x10/0x12
Nov 7 10:05:36 host kernel: [<c041ddd8>] ? __wake_up_common+0x35/0x5b
Nov 7 10:05:36 host kernel: [<c0423172>] ? __wake_up+0x28/0x32
Nov 7 10:05:36 host kernel: [<c0554f2e>] ? n_tty_receive_buf
+0xfa9/0xff7
Nov 7 10:05:36 host kernel: [<c0554f2e>] ? n_tty_receive_buf
+0xfa9/0xff7
Nov 7 10:05:36 host kernel: [<c0447cef>] ? rt_mutex_up_read+0x1b7/0x25d
Nov 7 10:05:36 host kernel: [<c0448f40>] ? rt_up_read+0x8/0xa
Nov 7 10:05:36 host kernel: [<c0647c26>] ? do_page_fault+0x45f/0x7d8
Nov 7 10:05:36 host kernel: [<c0502f6c>] ? copy_to_user+0x36/0x106
Nov 7 10:05:36 host kernel: [<c0644770>] ? rt_spin_lock_slowlock
+0x1bd/0x1d8
Nov 7 10:05:36 host kernel: [<c06456c1>] ? __rt_spin_lock+0x24/0x61
Nov 7 10:05:36 host kernel: [<c0645736>] ? rt_spin_lock+0x38/0x3b
Nov 7 10:05:36 host kernel: [<f8971c46>] ? snd_seq_fifo_cell_out
+0x47/0xee [snd_seq]
Nov 7 10:05:36 host kernel: [<c0425c81>] ? default_wake_function
+0x0/0x12
Nov 7 10:05:36 host kernel: [<f896f041>] ? snd_seq_read+0x0/0x1d8
[snd_seq]
Nov 7 10:05:36 host kernel: [<f896f11e>] ? snd_seq_read+0xdd/0x1d8
[snd_seq]
Nov 7 10:05:36 host kernel: [<c04d73d3>] ? security_file_permission
+0xf/0x11
Nov 7 10:05:36 host kernel: [<c045e231>] ? audit_syscall_entry
+0xf9/0x123
Nov 7 10:05:36 host kernel: [<c049606a>] sys_poll+0x3a/0x6a
Nov 7 10:05:36 host kernel: [<c0404be6>] syscall_call+0x7/0xb
Nov 7 10:05:36 host kernel: =======================
--------

# cat /proc/5256/status
Name: aseqdump
State: D (disk sleep)
Tgid: 5256
Pid: 5256
PPid: 5185
TracerPid: 0
Uid: 743 743 743 743
Gid: 10 10 10 10
FDSize: 32
Groups: 10 11 30 31 400
VmPeak: 3104 kB
VmSize: 3048 kB
VmLck: 0 kB
VmHWM: 884 kB
VmRSS: 884 kB
VmData: 172 kB
VmStk: 84 kB
VmExe: 12 kB
VmLib: 2700 kB
VmPTE: 20 kB
Threads: 1
SigQ: 1/32768
SigPnd: 0000000000000000
ShdPnd: 0000000000004000
SigBlk: 0000000000000000
SigIgn: 0000000000000000
SigCgt: 0000000180004002
CapInh: 0000000000000000
CapPrm: 0000000000000000
CapEff: 0000000000000000
CapBnd: ffffffffffffffff
Cpus_allowed: 0000000f
Cpus_allowed_list: 0-3
Mems_allowed: 1
Mems_allowed_list: 0
voluntary_ctxt_switches: 66283
nonvoluntary_ctxt_switches: 4

# cat /proc/5256/wchan
msleep

-- Fernando