linux-kernel - Re: [PATCH 07/19] x86/dumpstack: add IRQ_USABLE_STACK

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Date:	Fri, 22 Jul 2016 10:24:46 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Josh Poimboeuf <jpoimboe@...hat.com>
Cc:	Andy Lutomirski <luto@...capital.net>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H . Peter Anvin" <hpa@...or.com>, X86 ML <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Brian Gerst <brgerst@...il.com>,
	Kees Cook <keescook@...omium.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Byungchul Park <byungchul.park@....com>
Subject: Re: [PATCH 07/19] x86/dumpstack: add IRQ_USABLE_STACK_SIZE define

* Josh Poimboeuf <jpoimboe@...hat.com> wrote:

> > >         irq_stack_end   = (unsigned long *)(per_cpu(irq_stack_ptr, cpu));
> > > -       irq_stack       = (unsigned long *)(per_cpu(irq_stack_ptr, cpu) - IRQ_STACK_SIZE);
> > > +       irq_stack       = (unsigned long *)(per_cpu(irq_stack_ptr, cpu) -
> > > +                         IRQ_USABLE_STACK_SIZE);
> > 
> > This is different.
> 
> If nobody knows the reason for it, I may just remove it.  It doesn't
> seem to blow anything up on my system.  I tried digging through the git
> history but it's been there since the beginning of git time.

Please do any behavioral changes in separate patches - ordered after all the 'does 
not change behavior' low-risk patches.

I.e. try to order the patches by risk: (near-)zero-risk ones first, followed by 
lower risk ones, closed by higher risk ones. This makes both review, application 
of the patches and any bisection/fixing work later on easier.

If you ever see a good chance to split a patch that changes behavior into a 
zero-risk and a low-risk component, do so - we'd rather err on the side of being 
too finegrained in a series than having to scratch heads when bisecting to overly 
large patches.

Thanks,

	Ingo