linux-kernel - Re: [PATCH] mm: unhide get_dump

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Message-ID: <6EA7241F-A4B0-400C-B338-C375512727B5@juniper.net>
Date: Mon, 24 Feb 2025 18:42:49 +0000
From: Brian Mak <makb@...iper.net>
To: Arnd Bergmann <arnd@...nel.org>
CC: Andrew Morton <akpm@...ux-foundation.org>, Kees Cook <kees@...nel.org>,
        Arnd Bergmann <arnd@...db.de>, David Hildenbrand <david@...hat.com>,
        Peter Xu
	<peterx@...hat.com>, Jason Gunthorpe <jgg@...pe.ca>,
        John Hubbard
	<jhubbard@...dia.com>,
        Steve Sistare <steven.sistare@...cle.com>,
        Vivek
 Kasireddy <vivek.kasireddy@...el.com>,
        Yang Shi
	<yang@...amperecomputing.com>,
        Christophe Leroy
	<christophe.leroy@...roup.eu>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm: unhide get_dump_page() function

On Feb 24, 2025, at 7:12 AM, Arnd Bergmann <arnd@...nel.org> wrote:

> The definition of get_dump_page() is guarded by CONFIG_ELF_CORE, but
> the caller has now moved into a function that is built based on
> CONFIG_COREDUMP, which leads to a possible link failure:
> 
> ld.lld-21: error: undefined symbol: get_dump_page
>>>> referenced by coredump.c
>>>>              fs/coredump.o:(dump_vma_snapshot) in archive vmlinux.a

Kernel test robot reported this issue yesterday here:
https://lore.kernel.org/oe-kbuild-all/202502231914.ROOVWMZN-lkp@intel.com/
https://lore.kernel.org/oe-kbuild-all/202502231818.fP8cuxmf-lkp@intel.com/

> Change the #ifdef block around the definition to match the caller.
> In practice there is very little difference, as setting COREDUMP
> but not ELF_CORE is not useful.

Good catch! I wonder if we should guard the sparse dump size calculation
logic from the get_dump_page() caller behind CONFIG_ELF_CORE instead
though. I guess the question becomes, will we ever have a non-ELF core
dump format that won't skip zero pages?

Anyway, I'm fine with this fix as-is.