Tips on debugging suspend/resume failure

Tips on debugging suspend/resume failure

[Man Spaz]

Hello
I have a machine x86 arch with no serial port, only console. I have a suspend/resume (mem, not hibernate) problem (not sure which one it is, if something fails on the suspend, or the resume fails - but it does seem to go to sleep) that doesn't suspend nor resume at all, using stock standard x86_64 kernel.

I compiled everything as a module and removed all unnecessary ones, so I cannot isolate the problem to a specific driver. This very same machine had no problems with <2.6.34.2 kernels.

But the question remains, how to get debug out? Is there a dmesg buffer that can persist if DRAM is being refreshed perhaps? Is there another way to skin this mongrel, I mean cat?
Spaz


      


      

Re: Tips on debugging suspend/resume failure

[Chris Ball]

Hi,

   > But the question remains, how to get debug out? Is there a dmesg
   > buffer that can persist if DRAM is being refreshed perhaps?

The most promising attempts involve using GPU RAM to store dmesg,
since it persists across a soft reboot and isn't going to be
overwritten as long as you get to it before the video driver does
after the crash.  (Which you can ensure by blacklisting the driver.)

   > Is there another way to skin this mongrel, I mean cat? 

The most basic tool is probably CONFIG_PM_TRACE, which uses the
real-time clock to store a signature for the last driver to init
during suspend/resume -- after the crash, the kernel will interpret
the RTC hash it placed to give you a hint as to what might be failing.

The real answer, though, is to just keep trying to find any way at all
to get usable serial output, including by finding a different machine
with the same problem that has a serial port.

- Chris.
-- 
Chris Ball   <cjb@laptop.org>   <http://printf.net/>
One Laptop Per Child

Re: Tips on debugging suspend/resume failure

[Pavel Machek]

Hi!

> I have a machine x86 arch with no serial port, only console. I have a suspend/resume (mem, not hibernate) problem (not sure which one it is, if something fails on the suspend, or the resume fails - but it does seem to go to sleep) that doesn't suspend nor resume at all, using stock standard x86_64 kernel.
> 
> I compiled everything as a module and removed all unnecessary ones, so I cannot isolate the problem to a specific driver. This very same machine had no problems with <2.6.34.2 kernels.
> 
> But the question remains, how to get debug out? Is there a dmesg buffer that can persist if DRAM is being refreshed perhaps? Is there another way to skin this mongrel, I mean cat?
>

git bisect ?

Also you could try to blink keyboard leds, beep the speaker or debug
using 'hang/reboot' trick.

									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

Re: Tips on debugging suspend/resume failure

[Lima Union]

Just to let you know that I'm experiencing a similar problem, upon
resuming from s2ram the machine just gets stuck (no access thru
keyboard nor ssh, just replies from ping). The latest kernel that I
can use without this problem is 2.6.33.7 (rock solid), all newer
kernels that I tried after that one have the same issue (included
2.6.35.6) in a random way, ie: in ten suspend/resume cycles it may
happen once. I'm not a programmer so I can't really help here. (I'm
not subscribed to LKML).
Regards.LU.