linux-kernel - Re: [PATCH] slab: remove store

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Date:   Tue, 16 Apr 2019 23:21:26 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Vlastimil Babka <vbabka@...e.cz>
cc:     Qian Cai <cai@....pw>, akpm@...ux-foundation.org, luto@...nel.org,
        jpoimboe@...hat.com, sean.j.christopherson@...el.com,
        penberg@...nel.org, rientjes@...gle.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] slab: remove store_stackinfo()

On Tue, 16 Apr 2019, Vlastimil Babka wrote:
> On 4/16/2019 8:50 PM, Thomas Gleixner wrote:
> > On Tue, 16 Apr 2019, Vlastimil Babka wrote:
> > 
> >> On 4/16/19 4:22 PM, Qian Cai wrote:
> >>> store_stackinfo() does not seem used in actual SLAB debugging.
> >>> Potentially, it could be added to check_poison_obj() to provide more
> >>> information, but this seems like an overkill due to the declining
> >>> popularity of the SLAB, so just remove it instead.
> >>>
> >>> Signed-off-by: Qian Cai <cai@....pw>
> >>
> >> I've acked Thomas' version already which was narrower, but no objection
> >> to remove more stuff on top of that. Linus (and I later in another
> >> thread) already pointed out /proc/slab_allocators. It only takes a look
> >> at add_caller() there to not regret removing that one.
> > 
> > The issue why I was looking at this was a krobot complaint about the kernel
> > crashing in that stack store function with my stackguard series applied. It
> > was broken before the stackguard pages already, it just went unnoticed.
> > 
> > As you explained, nobody is caring about DEBUG_SLAB + DEBUG_PAGEALLOC
> > anyway, so I'm happy to not care about krobot tripping over it either.
> > 
> > So we have 3 options:
> > 
> >    1) I ignore it and merge the stack guard series w/o it
> > 
> >    2) I can carry the minimal fix or Qian's version in the stackguard
> >       branch
> > 
> >    3) We ship that minimal fix to Linus right now and then everyone can
> >       base their stuff on top independently.
> 
> I think #3 is overkill for something that was broken for who knows how long and
> nobody noticed. I'd go with 2) and perhaps Qian's version as nobody AFAIK uses
> the caller+cpu as well as the stack trace.
> 
> For Qian's version also:
> Acked-by: Vlastimil Babka <vbabka@...e.cz>

Ok. I'll pick it up and base the stackguard stuff on top.

Thanks,

	tglx