Re: [PATCHv2] mm/sparse: reset section's mem_map when fully deactivated

[Andrew Morton <akpm@linux-foundation.org>]

On Mon, 20 Jan 2020 08:29:39 +0100 Michal Hocko <mhocko@suse.com> wrote:

> On Mon 20-01-20 10:33:14, Pingfan Liu wrote:
> > After commit ba72b4c8cf60 ("mm/sparsemem: support sub-section hotplug"),
> > when a mem section is fully deactivated, section_mem_map still records the
> > section's start pfn, which is not used any more and will be reassigned
> > during re-added.
> > 
> > In analogy with alloc/free pattern, it is better to clear all fields of
> > section_mem_map.
> > 
> > Beside this, it breaks the user space tool "makedumpfile" [1], which makes
> > assumption that a hot-removed section has mem_map as NULL, instead of
> > checking directly against SECTION_MARKED_PRESENT bit. (makedumpfile will be
> > better to change the assumption, and need a patch)
> > 
> > The bug can be reproduced on IBM POWERVM by "drmgr -c mem -r -q 5" ,
> > trigger a crash, and save vmcore by makedumpfile
> 
> While makedumpfile lives very closely to the kernel and occasional
> breakage is to be expected I still believe that Fixes: ba72b4c8cf60
> is due.

But not a cc:stable?