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

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Date:   Thu, 18 Apr 2019 09:52:01 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     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 Thu, Apr 18, 2019 at 10:41:47AM +0200, Thomas Gleixner wrote:
> All architectures which support stacktrace carry duplicated code and
> do the stack storage and filtering at the architecture side.
> 
> Provide a consolidated interface with a callback function for consuming the
> stack entries provided by the architecture specific stack walker. This
> removes lots of duplicated code and allows to implement better filtering
> than 'skip number of entries' in the future without touching any
> architecture specific code.
> 
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> Cc: linux-arch@...r.kernel.org

This is a step in the right direction, especially if it allows us to get
rid of the 'skip' stuff.  But I'm not crazy about the callbacks.

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:


struct unwind_state state;

void unwind_start(struct unwind_state *state, struct task_struct *task,
		  struct pt_regs *regs, unsigned long *first_frame);

bool unwind_next_frame(struct unwind_state *state);

inline bool unwind_done(struct unwind_state *state);


Not only would it avoid the callbacks (which is a nice benefit already),
it would also allow the interfaces to be used outside of the
stack_trace_*() interfaces.  That would come in handy in cases like the
ftrace stack tracer code, which needs more than the stack_trace_*() API
can give.

Of course, this may be more work than what you thought you signed up for
;-)

-- 
Josh