linux-kernel - Re: [PATCH] mm/slab: Do not hash pointers when debugging slab

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Date:   Mon, 11 Dec 2017 06:00:40 -0600 (CST)
From:   Christopher Lameter <cl@...ux.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
cc:     Geert Uytterhoeven <geert+renesas@...der.be>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Tobin C . Harding" <me@...in.cc>, linux-mm <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm/slab: Do not hash pointers when debugging slab

On Sun, 10 Dec 2017, Linus Torvalds wrote:

> On Thu, Dec 7, 2017 at 2:17 AM, Geert Uytterhoeven
> <geert+renesas@...der.be> wrote:
> >
> >         if (cachep->flags & SLAB_STORE_USER) {
> > -               pr_err("Last user: [<%p>](%pSR)\n",
> > +               pr_err("Last user: [<%px>](%pSR)\n",
> >                        *dbg_userword(cachep, objp),
> >                        *dbg_userword(cachep, objp));
>
> Is there actually any point to the %px at all?
>
> Why not remove it? the _real_ information is printed out by %pSR, and
> that's both sufficient and useful in ways %px isn't.

This pointer refers to code so we can remove it.

>
> > -                               pr_err("Slab corruption (%s): %s start=%p, len=%d\n",
> > +                               pr_err("Slab corruption (%s): %s start=%px, len=%d\n",
> >                                        print_tainted(), cachep->name,
> >                                        realobj, size);
>
> and here, is the pointer actually interesting, or should we just give
> the offset to the allocation?
>
> But if the pointer is interesting, then ack.

The pointer here is to an slab object which could be important if one
wants to find the pointer value  in a hexdump of another object (f.e.
listhead) or other pointer information that is being inspected
in a debugging session.