[alsa-devel] [PATCH 2/2] ASoC: DAPM - Make sure DAPM widget IO ops hold the component mutex.

[Timur Tabi]

Liam Girdwood wrote:
> Can you switch on the mutex debugging kernel config here.  I've just had
> a quick look and the WM8776 and its not holding the codec mutex or
> calling snd_soc_update_bits_locked() so it must deadlock via another
> path.

Enabling the debug options didn't reveal anything, unfortunately.

When I start playback, here's the code flow:


dapm_seq_run_coalesced:1138
soc_widget_update_bits_locked:244
soc_widget_lock:211 codec=wm8776.1-001a platform=

The numbers are line numbers of the printk statements I added.

What happens is that the thread hangs on:

	mutex_lock(&w->codec->mutex);

in soc_widget_lock().

After a couple minutes, I see this:

INFO: task speaker-test:2624 blocked for more than 120 seconds.
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
speaker-test    D 0fced718     0  2624   2623 0x00000000
Call Trace:
[e6f27ab0] [c0038d5c] console_unlock+0x22c/0x29c (unreliable)
[e6f27b70] [c0008520] __switch_to+0x70/0x144
[e6f27b90] [c04ab830] __schedule+0x224/0x4ec
[e6f27be0] [c04aa6a8] mutex_lock_nested+0x188/0x394
[e6f27c40] [c0395c40] soc_widget_update_bits_locked+0x2b0/0x2c4
[e6f27c80] [c0397734] dapm_seq_run_coalesced.clone.24+0x1b8/0x1c4
[e6f27cc0] [c03977e4] dapm_seq_run.clone.25+0xa4/0x3c0
[e6f27d10] [c0397eb4] dapm_power_widgets+0x3b4/0x67c
[e6f27d70] [c0399480] snd_soc_dapm_stream_event+0x74/0xdc
[e6f27d90] [c039abb0] soc_pcm_prepare+0x108/0x1dc
[e6f27dc0] [c0378248] snd_pcm_do_prepare+0x24/0x5c
[e6f27dd0] [c0377e3c] snd_pcm_action_single+0x4c/0xb4
[e6f27df0] [c0379218] snd_pcm_action_nonatomic+0x7c/0xa0
[e6f27e10] [c037b678] snd_pcm_common_ioctl1+0x8f8/0x10d8
[e6f27e60] [c037c568] snd_pcm_playback_ioctl1+0x40/0x6cc
[e6f27ea0] [c00f0e20] do_vfs_ioctl+0xa4/0x7d0
[e6f27f10] [c00f158c] sys_ioctl+0x40/0x88
[e6f27f40] [c000f6e4] ret_from_syscall+0x0/0x3c
--- Exception: c01 at 0xfced718
    LR = 0xfd76a24
INFO: lockdep is turned off.




-- 
Timur Tabi
Linux kernel developer at Freescale