On Thu 16-01-20 11:01:08, Pingfan Liu wrote:
> When fully deactivated, it is meaningless to keep the value of a section's
> mem_map. And its mem_map will be reassigned during re-added.
>
> Beside this, it breaks the user space tool "makedumpfile", which makes
> assumption that a hot-removed section having mem_map as NULL.
We used to do that before ba72b4c8cf60 ("mm/sparsemem: support
sub-section hotplug"). Dan was this an intentional change?
> The bug can be reproduced on IBM POWERVM by "drmgr -c mem -r -q 5" ,
> trigger a crash, and save vmcore by makedumpfile
>
> Signed-off-by: Pingfan Liu <kernelfans@xxxxxxxxx>
> To: linux-mm@xxxxxxxxx
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: David Hildenbrand <david@xxxxxxxxxx>
> Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
> Cc: Oscar Salvador <osalvador@xxxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxxxxx>
> Cc: kexec@xxxxxxxxxxxxxxxxxxx
> Cc: Kazuhito Hagio <k-hagio@xxxxxxxxxxxxx>
> ---
> mm/sparse.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/mm/sparse.c b/mm/sparse.c
> index 3822ecb..fddac80 100644
> --- a/mm/sparse.c
> +++ b/mm/sparse.c
> @@ -789,7 +789,7 @@ static void section_deactivate(unsigned long pfn, unsigned long nr_pages,
> ms->usage = NULL;
> }
> memmap = sparse_decode_mem_map(ms->section_mem_map, section_nr);
> - ms->section_mem_map = sparse_encode_mem_map(NULL, section_nr);
> + ms->section_mem_map = NULL;
> }
>
> if (section_is_early && memmap)
> --
> 2.7.5
--
Michal Hocko
SUSE Labs
