Re: [PATCH 2/3] powerpc/xmon: drop the nobt option from xmon plus minor fixes

["Guilherme G. Piccoli" <gpiccoli@linux.vnet.ibm.com>]

On 02/21/2017 02:16 AM, Michael Ellerman wrote:
> "Guilherme G. Piccoli" <gpiccoli@linux.vnet.ibm.com> writes:
>> Subject: Re: [PATCH 2/3] powerpc/xmon: drop the nobt option from xmon plus minor fixes
> 
> In future please use the same version number for all patches of a
> series.
> 
> ie. This should include a v2, like the rest of the patches in the series.
> 
> It confuses the tools to have "v2 1/3" "2/3" "v2 3/3".
> 
> I realise that might seem a little odd when a patch is new to the
> series, but the version is the version *of the series*, not the
> individual patches.
> 
> For a new patch you can just add after the change log:
> 
> ---
> v2: New for v2 of the series.
> 
> 
> For example.

Sure, thanks for the hint and for explain very well how I should
proceed! Unfortunately...as you probably already noticed, I'm only
seeing this after sent the v2 of the series heheh
Sorry, next time I'll follow your suggestion (TBH I thought of it before
sending this, but I got more inclined in mess with the series numbering
heheh)

> 
>> The xmon parameter nobt was added long time ago, by commit 26c8af5f01df
>> ("[POWERPC] print backtrace when entering xmon"). The problem that time
>> was that during a crash in a machine with USB keyboard, xmon wouldn't
>> respond to commands from the keyboard, so printing the backtrace wouldn't
>> be possible.
>>
>> Idea then was to show automatically the backtrace on xmon crash for the
>> first time it's invoked (if it recovers, next time xmon won't show
>> backtrace automatically). The nobt parameter was added _only_ to prevent
>> this automatic trace show. Seems long time ago USB keyboards didn't work
>> that well!
>>
>> We don't need it anymore, but the feature of auto showing the backtrace
>> on first crash seems interesting (imagine a case of auto-reboot script),
>> so this patch keeps the functionality, yet removes the nobt parameter.
> 
> 
> I'm going to take this as-is, because I want to get it in for v4.11.
> 
> But I don't think we need the auto back trace logic at all. If anything
> it's an anti-feature IMHO.
> 
> Imagine you're debugging a machine and you drop into xmon to check
> something, then drop out again.
> 
> Then you go away and leave the box, and it crashes into xmon, but xmon
> doesn't print a backtrace because you've already been in xmon. Usually
> you can just get on the console and hit 't', but sometimes the machine
> crashes so hard that xmon doesn't take input - in which case you now
> have no backtrace. :sadface:
> 
> So I'll send a follow-up patch to remove the auto backtrace stuff
> completely and see if anyone objects.
> 

OK, guess you noticed in your next message I kept the trace
behavior...let's discuss there =)

Cheers,


Guilherme
> cheers
>