Comment # 9 on bug 935086 from Takashi Iwai

(In reply to Uwe Geuder from comment #8)
> Created attachment 638634 [details]
> screen picture when resume from hibernate hangs + SysRq
> 
> I use systemctl hibernate to hibernate the system. (Originally I used KDE
> desktop to call hibernate from the GUI. The hang existed already there with
> the same symptoms. Recently I have switched to i3 window manager and I call
> systemctl hibernate from command line).
> 
> When the system hangs in resume SysRq just prints the headlines, but no
> information. (see attached screen shot) What does that mean?

Is quiet boot option removed?
Also, increase the log level via alt-sysrq-8 or 9 beforehand.

> While experimenting with SysRq I noticed that "SysRq i" (SIGKILL to all)
> makes the resume complete. (tried twice, worked twice) The system seemed
> functional after that, but I did not dare to really use it, because I'm not
> sure what might be in an inconsistent state after the killing. What can we
> learn from that? I guess it means that the hang was still in initramfs, so
> killing all initramfs processes made it resuming the real root. But I don't
> understand the details how the real root could come up when everything is
> killed. 

The kernel already started to the resume, as its prompt already shows.  But I
wonder how the remote file system message appears *after* it.  So, this looks
like that two things are running concurrently and conflicting.

> (After the resume had completed SysRq showed the complete information, not
> just the headlines.
> 
> I also tried "echo disk | sudo tee /sys/power/state". In this case the
> system does not hang when resuming. What do we learn from that?

What if you pass resumedelay=10 boot option?  This will delay the resume in 10
seconds after kicked off.