linux-kernel - Re: [PATCH] mm: slub: print_hex_dump() with DUMP_PREFIX

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Date:   Sat, 21 Sep 2019 02:08:59 -0700 (PDT)
From:   David Rientjes <rientjes@...gle.com>
To:     Miles Chen <miles.chen@...iatek.com>
cc:     Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-mediatek@...ts.infradead.org, wsd_upstream@...iatek.com
Subject: Re: [PATCH] mm: slub: print_hex_dump() with DUMP_PREFIX_OFFSET

On Fri, 20 Sep 2019, Miles Chen wrote:

> Since commit ad67b74d2469d9b8 ("printk: hash addresses printed with %p"),
> The use DUMP_PREFIX_OFFSET instead of DUMP_PREFIX_ADDRESS with
> print_hex_dump() can generate more useful messages.
> 
> In the following example, it's easier get the offset of incorrect poison
> value with DUMP_PREFIX_OFFSET.
> 
> Before:
> Object 00000000e817b73b: 00 00 00 00 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b
> Object 00000000816f4601: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b
> Object 00000000169d2bb8: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b
> Object 00000000f4c38716: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b
> Object 00000000917e3491: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b
> Object 00000000c0e33738: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b
> Object 000000001755ddd1: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b
> 
> After:
> Object 00000000: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b
> Object 00000010: 63 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b
> Object 00000020: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b
> Object 00000030: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b a5
> 
> I think it might be worth to convert all DUMP_PREFIX_ADDRESS to
> DUMP_PREFIX_OFFSET for the whole Linux kernel.
> 

I agree it looks nicer for poisoning, I'm not sure that every caller of 
print_section() is the same, however.  For example trace() seems better 
off as DUMP_PREFIX_ADDRESS since it already specifies the address of the 
object being allocated or freed and offset here wouldn't really be useful, 
no?