linux-kernel - Re: [patch V2 28/29] stacktrace: Provide common infrastructure

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Message-ID: <alpine.DEB.2.21.1904191031390.3174@nanos.tec.linutronix.de>
Date:   Fri, 19 Apr 2019 10:32:30 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Peter Zijlstra <peterz@...radead.org>
cc:     LKML <linux-kernel@...r.kernel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>, x86@...nel.org,
        Andy Lutomirski <luto@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Alexander Potapenko <glider@...gle.com>,
        linux-arch@...r.kernel.org, Alexey Dobriyan <adobriyan@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Pekka Enberg <penberg@...nel.org>, linux-mm@...ck.org,
        David Rientjes <rientjes@...gle.com>,
        Christoph Lameter <cl@...ux.com>,
        Catalin Marinas <catalin.marinas@....com>,
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Subject: Re: [patch V2 28/29] stacktrace: Provide common infrastructure

On Fri, 19 Apr 2019, Peter Zijlstra wrote:
> On Thu, Apr 18, 2019 at 10:41:47AM +0200, Thomas Gleixner wrote:
> 
> > +typedef bool (*stack_trace_consume_fn)(void *cookie, unsigned long addr,
> > +                                      bool reliable);
> 
> > +void arch_stack_walk(stack_trace_consume_fn consume_entry, void *cookie,
> > +		     struct task_struct *task, struct pt_regs *regs);
> > +int arch_stack_walk_reliable(stack_trace_consume_fn consume_entry, void *cookie,
> > +			     struct task_struct *task);
> 
> This bugs me a little; ideally the _reliable() thing would not exists.
> 
> Thomas said that the existing __save_stack_trace_reliable() is different
> enough for the unification to be non-trivial, but maybe Josh can help
> out?
> 
> >From what I can see the biggest significant differences are:
> 
>  - it looks at the regs sets on the stack and for FP bails early
>  - bails for khreads and idle (after it does all the hard work!?!)
> 
> The first (FP checking for exceptions) should probably be reflected in
> consume_fn(.reliable) anyway -- although that would mean a lot of extra
> '?' entries where there are none today.
> 
> And the second (KTHREAD/IDLE) is something that the generic code can
> easily do before calling into the arch unwinder.

And looking at the powerpc version of it, that has even more interesting
extra checks in that function.

Thanks,

	tglx