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

Fernando Lopez-Lezcano
2008-11-14T00:13:16Z

On Thu, 2008-11-13 at 14:56 -0800, Fernando Lopez-Lezcano wrote:
> On Thu, 2008-11-13 at 13:01 -0800, Fernando Lopez-Lezcano wrote:
> > 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).
> > >
> > > > ... 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.
> >
> > Going back to this in the hope of a bit more data helping solve the
> > problem...
> >
> > I don't understand what is going on (of course! :-)
> >
> > Cards look like this:
> >
> > $ cat /proc/asound/cards
> > 0 [Gina3G ]: Echo_Echo3G - Gina3G
> > Gina3G rev.0 (DSP56361) at 0xfeb00000 irq 18
> > 1 [Intel ]: HDA-Intel - HDA Intel
> > HDA Intel at 0xfe7f8000 irq 22
> > 2 [PCR ]: USB-Audio - PCR
> > EDIROL PCR at usb-0000:00:1d.0-1, full speed
> >
> > Here's what I do:
> > - start aseqdump
> > - aconnect 16:0 128:0
> > - aseqdump receives one midi message (one byte active sensing msg)
> > - aseqdump hangs forever (reboot needed)
> >
> > This is what dmesg prints (patch attached which shows where the printk's
> > are located in the source for rawmidi.c and seq_midi.c):
>
> More info with some more printk's (see attached patch for location):

I've been trying to follow the printk crumbs without much success.
AFAICT it all points to tasklet_hi_schedule ... the handling code is
being scheduled but never executes, right? (well, it executes _once_ and
then never again). And that leads to tasklet_common_schedule - as
Clemens pointed at the beginning of the thread this is eerily similar to
what happened before in 2006:

http://lkml.org/lkml/2006/3/7/256

So, is tasklet_common_schedule just going through the "goto again;" loop
forever?:

tasklet_trylock(t) is true
again:
-> test_bit(TASKLET_STATE_SCHED, &t->state) is false
-> !tasklet_tryunlock(t) is true
-> goto again

I don't know what it all _means_, I'm just trying to point a finger to
something in the hope that somebody will understand and say "aha!" (and
email a nice patch! :-)

As the code says, "this is subtle"...

-- Fernando

> after aseqdump startup:
>
> snd_seq_fifo: before init
> snd_seq_fifo: after init
> snd_seq_fifo_poll_wait: before poll_wait
> snd_seq_fifo_poll_wait: after poll_wait
>
> after aconnect:
>
> snd_seq_fifo: before init
> snd_seq_fifo: after init
> rawmidi: before input ops trigger
> rawmidi: after input ops trigger
> rawmidi: before input ops trigger
> rawmidi: after input ops trigger
> snd_seq_fifo_event_in: before wake_up
> snd_seq_fifo_event_in: after wake_up
> snd_seq_fifo_poll_wait: before poll_wait
> snd_seq_fifo_poll_wait: after poll_wait
> snd_seq_fifo_cell_out: before spin_unlock
> snd_seq_fifo_cell_out: after spin_unlock
> snd_seq_fifo_poll_wait: before poll_wait
> snd_seq_fifo_poll_wait: after poll_wait
> rawmidi: before receive spinlock
> rawmidi: after receive spinlock
> rawmidi: about to run receive tasklet
> rawmidi: run receive tasklet
> rawmidi: before receive spin unlock
> rawmidi: after receive spin unlock
> rawmidi: about to run input tasklet
> seq: snd_midi_input_event called
> seq: seq_midi_input_event loop begin
> rawmidi: before input ops trigger
> rawmidi: after input ops trigger
> seq: snd_seq_kernel_client_dispatch called
> snd_seq_fifo_event_in: before wake_up
> snd_seq_fifo_event_in: after wake_up
> seq: snd_seq_kernel_client_dispatch returned
> snd_seq_fifo_poll_wait: before poll_wait
> snd_seq_fifo_poll_wait: after poll_wait
> seq: snd_midi_input_event exiting
> rawmidi: after running input tasklet
> snd_seq_fifo_cell_out: before spin_unlock
> snd_seq_fifo_cell_out: after spin_unlock
> snd_seq_fifo_poll_wait: before poll_wait
> snd_seq_fifo_poll_wait: after poll_wait
> rawmidi: before receive spinlock
> rawmidi: after receive spinlock
> rawmidi: about to run receive tasklet
> rawmidi: run receive tasklet
> rawmidi: before receive spin unlock
> rawmidi: after receive spin unlock
> rawmidi: before receive spinlock
> rawmidi: after receive spinlock
> rawmidi: about to run receive tasklet
> rawmidi: run receive tasklet
> rawmidi: before receive spin unlock
> rawmidi: after receive spin unlock
> rawmidi: before receive spinlock
> rawmidi: after receive spinlock
> rawmidi: about to run receive tasklet
>
> Hangs here:
>
> Nov 13 14:39:57 host kernel: aseqdump S [f55762f0] f714dbe0 0
> 5360 5318
> Nov 13 14:39:57 host kernel: f714dbd4 00200082 f628edc0 f714dbe0
> c042ab6d f55762f0 f5576584 c4847700
> Nov 13 14:39:57 host kernel: 00000001 c4847700 098b418d 0000003d
> 00000000 00000000 00200246 f63980f4
> Nov 13 14:39:57 host kernel: f714dbc0 c06456c1 f63980f4 f714dc5c
> f714dbcc 00000000 7fffffff f714de98
> Nov 13 14:39:57 host kernel: Call Trace:
> Nov 13 14:39:57 host kernel: [<c042ab6d>] ? vprintk+0x30e/0x331
> Nov 13 14:39:57 host kernel: [<c06456c1>] ? __rt_spin_lock+0x24/0x61
> Nov 13 14:39:57 host kernel: [<c0643ba5>] schedule+0xbf/0xd8
> Nov 13 14:39:57 host kernel: [<c0643c72>] schedule_timeout+0x17/0xbc
> Nov 13 14:39:57 host kernel: [<c0642de5>] ? printk+0xf/0x12
> Nov 13 14:39:57 host kernel: [<f8967c0c>] ? snd_seq_fifo_poll_wait
> +0x32/0x44 [snd_seq]
> Nov 13 14:39:57 host kernel: [<f8964fad>] ? snd_seq_poll+0x4d/0x9f
> [snd_seq]
> Nov 13 14:39:57 host kernel: [<c0495d92>] do_sys_poll+0x292/0x348
> Nov 13 14:39:57 host kernel: [<c0496be2>] ? __pollwait+0x0/0xb6
> Nov 13 14:39:57 host kernel: [<c0425c81>] ? default_wake_function
> +0x0/0x12
> Nov 13 14:39:57 host kernel: [<c0645736>] ? rt_spin_lock+0x38/0x3b
> Nov 13 14:39:57 host kernel: [<c04752f7>] ? page_address+0x88/0xaa
> Nov 13 14:39:57 host kernel: [<c047596d>] ? kmap_high+0x421/0x42a
> Nov 13 14:39:57 host kernel: [<c04ff574>] ? radix_valid_always+0x0/0xa
> Nov 13 14:39:57 host kernel: [<c046430b>] ? __rcu_read_unlock+0x6d/0x72
> Nov 13 14:39:57 host kernel: [<c04699ec>] ? find_get_page+0xfa/0x120
> Nov 13 14:39:57 host kernel: [<c0440314>] ? getnstimeofday+0x3c/0xd6
> Nov 13 14:39:57 host kernel: [<c043e653>] ? ktime_get_ts+0x4a/0x4e
> Nov 13 14:39:57 host kernel: [<c043e66a>] ? ktime_get+0x13/0x2f
> Nov 13 14:39:57 host kernel: [<c0424060>] ? hrtick_start_fair
> +0x140/0x148
> Nov 13 14:39:57 host kernel: [<c041f87b>] ? task_rq_lock+0x44/0x6e
> Nov 13 14:39:57 host kernel: [<c0425c76>] ? try_to_wake_up+0x212/0x21d
> Nov 13 14:39:57 host kernel: [<c0425c91>] ? default_wake_function
> +0x10/0x12
> Nov 13 14:39:57 host kernel: [<c041ddd8>] ? __wake_up_common+0x35/0x5b
> Nov 13 14:39:57 host kernel: [<c0423172>] ? __wake_up+0x28/0x32
> Nov 13 14:39:57 host kernel: [<c0554f2e>] ? n_tty_receive_buf
> +0xfa9/0xff7
> Nov 13 14:39:57 host kernel: [<c0554f2e>] ? n_tty_receive_buf
> +0xfa9/0xff7
> Nov 13 14:39:57 host kernel: [<c05009a6>] ? rb_insert_color+0x56/0xc0
> Nov 13 14:39:57 host kernel: [<c043dbab>] ? enqueue_hrtimer+0x112/0x11e
> Nov 13 14:39:57 host kernel: [<c043e441>] ? hrtimer_start+0x133/0x162
> Nov 13 14:39:57 host kernel: [<c04249d0>] ? hrtick_set+0x97/0xe5
> Nov 13 14:39:57 host kernel: [<c06456c1>] ? __rt_spin_lock+0x24/0x61
> Nov 13 14:39:57 host kernel: [<c0645736>] ? rt_spin_lock+0x38/0x3b
> Nov 13 14:39:57 host kernel: [<f8967c68>] ? snd_seq_fifo_cell_out
> +0x4a/0x146 [snd_seq]
> Nov 13 14:39:57 host kernel: [<c0425c81>] ? default_wake_function
> +0x0/0x12
> Nov 13 14:39:57 host kernel: [<f8965041>] ? snd_seq_read+0x0/0x1d8
> [snd_seq]
> Nov 13 14:39:57 host kernel: [<f896511e>] ? snd_seq_read+0xdd/0x1d8
> [snd_seq]
> Nov 13 14:39:57 host kernel: [<c04d73d3>] ? security_file_permission
> +0xf/0x11
> Nov 13 14:39:57 host kernel: [<c045e231>] ? audit_syscall_entry
> +0xf9/0x123
> Nov 13 14:39:57 host kernel: [<c049606a>] sys_poll+0x3a/0x6a
> Nov 13 14:39:57 host kernel: [<c0404be6>] syscall_call+0x7/0xb
> Nov 13 14:39:57 host kernel: =======================
>
> After I try to kill aseqdump:
>
> snd_seq_fifo_poll_wait: before poll_wait
> snd_seq_fifo_poll_wait: after poll_wait
> rawmidi: before input ops trigger
> rawmidi: after input ops trigger
> rawmidi: about to kill input tasklet
> (definitely hangs there as well, never kills tasklet)
>
> Help!
> What can I try next??
> -- Fernando
>
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