Recent Kernels failing to boot?

[nick]

On 14-09-02 08:01 PM, Jonghun John Park wrote:
> 
>> On 2014. 9. 2., at 20:14, John Whitmore <arigead at gmail.com> wrote:
>>
>> I'm not even sure that this is the correct home for this question but sure
>> it's worth a punt. I'm running OpenSUSE on a netbook and use it to compile and
>> install the latest kernel from Linus's git repo. This has always been a simple
>> operation pulling the latest, updating the config file, make and install.
>>
> 
> did you check what the log files (kernel.log or syslog) told you when you were building and Installing it?
> There were  No errors or warnings?
> 
>> A few versions ago I hit a snag in that once installed the new kernel would
>> show up in the grub2 menu but once selected for boot the machine would just go
>> to a blank screen and hang. I'd have to do a hard reset. I can't be specific
>> on which version this started happening on as the problem is intermittent. It
>> seems to be a race condition sometimes a kernel will boot and sometimes it
>> won't.
>>
> 
> Running grub2 means that your system cannot read grub.cfg because it has some flaws in most cases. The best way I can recommend you is that try booting with another bootable image and seeing if configuration file is well written unless you are familiar with grub syntax. Of course, you have to mount the root disk you were supposed to mount as a root.
> 
> 
>> I thought I could investigate this issue but I can't find any debug info for
>> this problem at all. grub2 is happy as it's handed control over to the kernel
>> but there's no evidence of any kernel activity in the logs at all for the
>> requested boot.
>>
> 
> If you had a logging setup via a serial port, you would never miss a line of debug info generated.
> Because it already logged tens of lines of debug info before it decided to load the bootstrap you were supposed to use.
> I hope the following link is helpful for you to get this right..
> 
> http://linuxdeveloper.blogspot.kr/2012/05/debugging-linux-kernel-over-serial-port.html 
> 
>> So the reason for this post is to ask if anybody could suggest how to debug
>> this issue. I think it came in about 3.14 but like I say it's intermittent.
>>
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Hey Guys,
I agree with Jonghun here and agree that getting this outputted to a serial port is of use to the kernel developers.
I also recommend reading the link and am going to check it out myself as I need to learn how to debug early boot code
myself :). In addition seems to be an issue with late stage grub or very early kernel as even printk_early is not showing anything and this means your serial port is not initialized on the computer being booted. If that's too 
hard, then run git bisect on the newest kernel tree and give it the last known good kernel version I believe
it's 3.12 or 3.13 from reading this. :) Then post the bad commit log and sha1-id here for us to see.
Cheers and Good Luck,
Nick