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

Michael Ellerman mpe at ellerman.id.au
Tue Feb 21 16:16:31 AEDT 2017

"Guilherme G. Piccoli" <gpiccoli at 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

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.

> 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.


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