Re: [PATCH] mm: slub: print_hex_dump() with DUMP_PREFIX_OFFSET

David Rientjes
2019-09-21T09:08:59Z

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?