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

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Message-ID: <20190419090717.GN7905@worktop.programming.kicks-ass.net>
Date:   Fri, 19 Apr 2019 11:07:17 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Thomas Gleixner <tglx@...utronix.de>
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>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        kasan-dev@...glegroups.com,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        Akinobu Mita <akinobu.mita@...il.com>,
        iommu@...ts.linux-foundation.org,
        Robin Murphy <robin.murphy@....com>,
        Christoph Hellwig <hch@....de>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Johannes Thumshirn <jthumshirn@...e.de>,
        David Sterba <dsterba@...e.com>, Chris Mason <clm@...com>,
        Josef Bacik <josef@...icpanda.com>,
        linux-btrfs@...r.kernel.org, dm-devel@...hat.com,
        Mike Snitzer <snitzer@...hat.com>,
        Alasdair Kergon <agk@...hat.com>,
        intel-gfx@...ts.freedesktop.org,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        dri-devel@...ts.freedesktop.org, David Airlie <airlied@...ux.ie>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>
Subject: Re: [patch V2 28/29] stacktrace: Provide common infrastructure

On Fri, Apr 19, 2019 at 10:32:30AM +0200, Thomas Gleixner wrote:
> 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.

Right, but not fundamentally different from determining @reliable I
think.

Anyway, it would be good if someone knowledgable could have a look at
this.