linux-kernel - Re: [PATCH v2] drivers/base/node.c: Simplify unregister_memory_block_under

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Message-Id: <20191127141532.525708b65a96fd614595bae8@linux-foundation.org>
Date:   Wed, 27 Nov 2019 14:15:32 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     David Hildenbrand <david@...hat.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Pavel Tatashin <pasha.tatashin@...een.com>,
        Michal Hocko <mhocko@...e.com>,
        Oscar Salvador <osalvador@...e.de>,
        Chris von Recklinghausen <crecklin@...hat.com>
Subject: Re: [PATCH v2] drivers/base/node.c: Simplify
 unregister_memory_block_under_nodes()

On Wed, 27 Nov 2019 17:53:12 +0100 David Hildenbrand <david@...hat.com> wrote:

> Just a note that this was actually also a bugfix as noted by Chris.
> 
> If the memory we are removing was never onlined,
> get_nid_for_pfn()->pfn_to_nid() will return garbage. Removing will
> succeed but links will remain in place.
> 
> Can be triggered by
> 
> 1. hotplugging a DIMM to node 1
> 2. not onlining the memory blocks
> 3. unplugging it
> 4. re-plugging it to node 1
> 
> We will trigger the BUG_ON(ret) in add_memory_resource(), because
> link_mem_sections() will return with -EEXIST.

Oh.  In that case case we please redo the patch as a bugfix? 
Appropriate title and changelog?  And perhaps the bugfix can be split
from the cleanup, to make the former more backportable?