How to debug pm-suspend freeze?

Question

Running 15.10 (32-bit) on a Dell Latitude D630, with kernel 4.2.0-30-generic.

When I run

sudo pm-suspend

or

# echo -n mem > /sys/power/state

the screen stops moving, mouse doesn't move, screen stays lit, keyboard and mouse do nothing, and remote (ssh) sessions become unresponsive.

/var/log/pm-suspend.log ends with:

Sun Feb 28 19:44:39 EST 2016: performing suspend

/var/log/kern.log seems to contain nothing related to suspend, though maybe someone could suggest what I might look for that could be related.

Modules are:

wl dell_wmi dell_rbtn dell_laptop sparse_keymap gpio_ich snd_hda_codec_hdmi snd_hda_codec_idt snd_hda_codec_generic pcmcia dcdbas snd_hda_intel dell_smm_hwmon snd_hda_codec coretemp snd_hda_core kvm snd_hwdep yenta_socket input_leds joydev cfg80211 serio_raw snd_pcm snd_seq_midi snd_seq_midi_event snd_rawmidi pcmcia_rsrc snd_seq lpc_ich pcmcia_core snd_seq_device snd_timer snd soundcore shpchp 8250_fintek mac_hid parport_pc ppdev lp parport autofs4 psmouse firewire_ohci firewire_core tg3 pata_acpi crc_itu_t ptp pps_core i915 wmi i2c_algo_bit drm_kms_helper syscopyarea video sysfillrect sysimgblt fb_sys_fops drm

I have seen many people suggest that the issue may be a particular module, and that solution is to edit /etc/pm/config.d/modules to add the module to SUSPEND_MODULES. However I have no idea which of the many modules might be the culprit. Is there some way I can get more debugging information out of suspend, so that I can figure out which module it might be?

Answer 1

I have found that

dmesg

and

cat /var/log/pm-suspend.log

tend to provide the most information. In the best-case scenario, the problem will be a process that failed to stop, and this will show up in dmesg. In the worst case, it will be a module. I haven't found a way to figure out which module, other than trial-and-error.

In my case it turned out to be the wl module (for the wireless card).