Kernel panic

I just came back to my desk after a few hours and my laptop would not
wake up.  The caps lock indicator was blinking.  I assumed this was a
kernel panic.

But why?

cal@flexo:~$ cat /var/log/syslog
Jan 20 01:35:41 flexo rsyslogd: [origin software="rsyslogd"
swVersion="8.16.0" x-pid="918" x-info="http://www.rsyslog.com"]
rsyslogd was HUPed
Jan 20 01:35:43 flexo anacron[905]: Job `cron.daily' terminated
Jan 20 01:35:43 flexo anacron[905]: Normal exit (1 job run)
Jan 20 01:36:27 flexo org.freedesktop.Notifications[1677]: Gtk-Message:
Failed to load module "topmenu-gtk-module"
Jan 20 01:37:29 flexo
org.mate.panel.applet.MateMenuAppletFactory[1677]: Gtk-Message: Failed
to load module "topmenu-gtk-module"
Jan 20 01:37:29 flexo kernel: [  439.971301] [drm:drm_edid_block_valid
[drm]] *ERROR* EDID checksum is invalid, remainder is 73
Jan 20 01:37:29 flexo kernel: [  439.971305] Raw EDID:
Jan 20 01:37:29 flexo kernel: [  439.971308]   00 ff ff ff ff ff
ff 00 19 c9 00 00 00 00 00 00
Jan 20 01:37:29 flexo kernel: [  439.971310]   00 14 01 03 08 00
00 78 0a 53 0d a0 54 46 94 27
Jan 20 01:37:29 flexo kernel: [  439.971311]   11 46 47 21 08 00
01 01 01 01 01 01 01 01 01 01
Jan 20 01:37:29 flexo kernel: [  439.971313]   01 01 01 01 01 01
66 21 50 b0 51 00 1b 30 40 70
Jan 20 01:37:29 flexo kernel: [  439.971315]   36 00 10 09 00 00
00 1e a9 1a 00 a0 50 00 16 30
Jan 20 01:37:29 flexo kernel: [  439.971316]   30 20 37 00 05 03
00 ff ff ff ff ff ff ff ff ff
Jan 20 01:37:29 flexo kernel: [  439.971318]   ff ff ff ff ff ff
ff ff ff ff ff ff ff ff ff ff
Jan 20 01:37:29 flexo kernel: [  439.971319]   ff ff ff ff ff ff
ff ff ff ff ff ff ff ff ff ff
Jan 20 01:37:30 flexo
org.mate.panel.applet.MateMenuAppletFactory[1677]: (evolution:2769): e-
data-server-WARNING **: e_module_load_all_in_directory: Falló al abrir
el directorio «/usr/lib/evolution-data-server/credential-modules»: No
existe el archivo o el directorio
Jan 20 01:37:30 flexo
org.mate.panel.applet.MateMenuAppletFactory[1677]: (evolution:2769):
camel-WARNING **: Failed to initialize NSS SQL database in
sql:/etc/pki/nssdb: NSS error -8126
Jan 20 01:37:32 flexo
org.mate.panel.applet.MateMenuAppletFactory[1677]: Gtk-Message: Failed
to load module "topmenu-gtk-module"
Jan 20 01:37:33 flexo kernel: [  443.495472] perf interrupt took too
long (2511 > 2500), lowering kernel.perf_event_max_sample_rate to 50000
Jan 20 01:45:37 flexo systemd[1]: Starting Cleanup of Temporary
Directories...
Jan 20 01:45:37 flexo systemd-tmpfiles[3007]:
[/usr/lib/tmpfiles.d/var.conf:14] Duplicate line for path "/var/log",
ignoring.
Jan 20 01:45:37 flexo systemd[1]: Started Cleanup of Temporary
Directories.
Jan 20 01:46:39 flexo kernel: [  989.652860] perf interrupt took too
long (5013 > 5000), lowering kernel.perf_event_max_sample_rate to 25000
cal@flexo:~$

Also, I noticed something strange in /var/log/syslog.1:

Jan 20 01:31:56 flexo ureadahead[342]: ureadahead:909/cmdline:
Ruta relativa ignorada
Jan 20 01:31:56 flexo ureadahead[342]: ureadahead:914/stat: Ruta
relativa ignorada
Jan 20 01:31:56 flexo ureadahead[342]: ureadahead:914/cmdline: Ruta
relativa ignorada
Jan 20 01:31:56 flexo ureadahead[342]: ureadahead:918/stat: Ruta
relativa ignorada
Jan 20 01:31:56 flexo ureadahead[342]: ureadahead:918/cmdline: Ruta
relativa ignorada
Jan 20 01:31:56 flexo ureadahead[342]: ureadahead:926/stat: Ruta
relativa ignorada
Jan 20 01:31:56 flexo ureadahead[342]: ureadahead:926/cmdline: Ruta
relativa ignorada
Jan 20 01:31:56 flexo ureadahead[342]: ureadahead:937/stat: Ruta
relativa ignorada
Jan 20 01:31:56 flexo ureadahead[342]: ureadahead:937/cmdline: Ruta
relativa ignorada
Jan 20 01:31:56 flexo ureadahead[342]: ureadahead:980/stat: Ruta
relativa ignorada
Jan 20 01:31:56 flexo ureadahead[342]: ureadahead:980/cmdline: Ruta
relativa ignorada
Jan 20 01:31:56 flexo ureadahead[342]: ureadahead:985/stat: Ruta
relativa ignorada
Jan 20 01:31:56 flexo ureadahead[342]: ureadahead:985/cmdline: Ruta
relativa ignorada
Jan 20 01:31:56 flexo ureadahead[342]: ureadahead:997/stat: Ruta
relativa ignorada
Jan 20 01:31:56 flexo ureadahead[342]: ureadahead:997/cmdline: Ruta
relativa ignorada
Jan 20 01:31:56 flexo ureadahead[342]: ureadahead:1001/stat: Ruta
relativa ignorada
Jan 20 01:31:56 flexo ureadahead[342]: ureadahead:1001/cmdline: Ruta
relativa ignorada
Jan 20 01:31:56 flexo ureadahead[342]: ureadahead:1013/stat: Ruta
relativa ignorada
Jan 20 01:31:56 flexo ureadahead[342]: ureadahead:1013/cmdline: Ruta
relativa ignorada
Jan 20 01:31:56 flexo ureadahead[342]: ureadahead:1101/stat: Ruta
relativa ignorada

What could be the cause of this?