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

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Date:   Fri, 19 Apr 2019 10:50:44 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>, 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 09:02:11AM +0200, Peter Zijlstra wrote:
> On Thu, Apr 18, 2019 at 05:42:55PM +0200, Thomas Gleixner wrote:
> > On Thu, 18 Apr 2019, Josh Poimboeuf wrote:
> 
> > > Another idea I had (but never got a chance to work on) was to extend the
> > > x86 unwind interface to all arches.  So instead of the callbacks, each
> > > arch would implement something like this API:
> 
> > I surely thought about that, but after staring at all incarnations of
> > arch/*/stacktrace.c I just gave up.
> > 
> > Aside of that quite some archs already have callback based unwinders
> > because they use them for more than stacktracing and just have a single
> > implementation of that loop.
> > 
> > I'm fine either way. We can start with x86 and then let archs convert over
> > their stuff, but I wouldn't hold my breath that this will be completed in
> > the forseeable future.
> 
> I suggested the same to Thomas early on, and I even spend the time to
> convert some $random arch to the iterator interface, and while it is
> indeed entirely feasible, it is _far_ more work.
> 
> The callback thing OTOH is flexible enough to do what we want to do now,
> and allows converting most archs to it without too much pain (as Thomas
> said, many archs are already in this form and only need minor API
> adjustments), which gets us in a far better place than we are now.
> 
> And we can always go to iterators later on. But I think getting the
> generic unwinder improved across all archs is a really important first
> step here.

Fair enough.

-- 
Josh