linux-kernel - Re: [PATCH v3 32/51] x86/dumpstack: simplify in_exception

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Date:	Sun, 14 Aug 2016 00:48:15 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Josh Poimboeuf <jpoimboe@...hat.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...nel.org>,
	"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>,
	Nilay Vaish <nilayvaish@...il.com>
Subject: Re: [PATCH v3 32/51] x86/dumpstack: simplify in_exception_stack()

On Fri, Aug 12, 2016 at 7:28 AM, Josh Poimboeuf <jpoimboe@...hat.com> wrote:
> in_exception_stack() does some bad, bad things just so the unwinder can
> print different values for different areas of the debug exception stack.
>
> There's no need to clarify where exactly on the stack it is.  Just print
> "#DB" and be done with it.

I'm okay with the printing part, but you're also using this to prevent
infinite looping.  Will this cause the unwind to fail if we go debug
-> page fault -> debug or similar?  (Or whatever actually uses the
deeper debug stacks?  I figured this out once and then forgot exactly
what's going on.  I really need to dust off my patches that stop using
IST for #DB.)

--Andy