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

[Christopher Lameter]

On Sun, 10 Dec 2017, Linus Torvalds wrote:

> On Thu, Dec 7, 2017 at 2:17 AM, Geert Uytterhoeven
> <geert+renesas@xxxxxxxxx> 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.