linux-kernel - Re: [PATCH 0/3] slub: Print non-hashed pointers in slub debugging

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Date:   Thu, 20 May 2021 12:01:20 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Stephen Boyd <swboyd@...omium.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-kernel@...r.kernel.org, Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>, linux-mm@...ck.org,
        Timur Tabi <timur@...nel.org>, Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Kees Cook <keescook@...omium.org>,
        Marco Elver <elver@...gle.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 0/3] slub: Print non-hashed pointers in slub debugging

+CC folks from the no_hash_pointers debate

Full thread with patches here:
https://lore.kernel.org/linux-mm/20210520013539.3733631-1-swboyd@chromium.org/

On 5/20/21 3:35 AM, Stephen Boyd wrote:
> I was doing some debugging recently and noticed that my pointers were
> being hashed while slub_debug was on the kernel commandline. Let's make
> the prints in here meaningful in that case by pushing %px throughout.

But we actually added no_hash_pointers exactly so that we don't push %px in
hexdump and others. So I don't think this will be accepted.

> Alternatively, we could force on no_hash_pointers if slub_debug is on
> the commandline. Maybe that would be better?

That would certainly be more acceptable, but maybe still too much, dunno. I'm
neutral on this approach, let's see what others think.

> The final patch is just something else I noticed while looking at the
> code. The message argument is never used so the debugging messages are
> not as clear as they could be.
> 
> Stephen Boyd (3):
>   lib/hexdump: Add a raw pointer printing format for slub debugging
>   slub: Print raw pointer addresses when debugging
>   slub: Actually use 'message' in restore_bytes()
> 
>  include/linux/printk.h |  1 +
>  lib/hexdump.c          | 12 ++++++++++--
>  mm/slub.c              | 24 ++++++++++++------------
>  3 files changed, 23 insertions(+), 14 deletions(-)
> 
> 
> base-commit: 6efb943b8616ec53a5e444193dccf1af9ad627b5
>