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.
> [1]: makedumpfile, commit e73016540293 ("[v1.6.7] Update version")
>
> Signed-off-by: Pingfan Liu <[email protected]>
> To: [email protected]
> Cc: Andrew Morton <[email protected]>
> Cc: David Hildenbrand <[email protected]>
> Cc: Dan Williams <[email protected]>
> Cc: Oscar Salvador <[email protected]>
> Cc: Michal Hocko <[email protected]>
> Cc: Baoquan He <[email protected]>
> Cc: Qian Cai <[email protected]>
> Cc: [email protected]
> Cc: Kazuhito Hagio <[email protected]>
Acked-by: Michal Hocko <[email protected]>
> ---
> v1 -> v2:
> make an explicit convertion from NULL to ulong
> improve commit log
>
> mm/sparse.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/mm/sparse.c b/mm/sparse.c
> index 3822ecb..3918fc3 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 = (unsigned long)NULL;
> }
>
> if (section_is_early && memmap)
> --
> 2.7.5
--
Michal Hocko
SUSE Labs
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