From: Pingfan Liu kernelfans@gmail.com Subject: mm/sparse.c: reset section's mem_map when fully deactivated

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-addition.

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

[1]: makedumpfile, commit e73016540293 ("[v1.6.7] Update version")

Link: http://lkml.kernel.org/r/1579487594-28889-1-git-send-email-kernelfans@gmail.... Signed-off-by: Pingfan Liu kernelfans@gmail.com Acked-by: Michal Hocko mhocko@suse.com Acked-by: David Hildenbrand david@redhat.com Cc: Dan Williams dan.j.williams@intel.com Cc: Oscar Salvador osalvador@suse.de Cc: Baoquan He bhe@redhat.com Cc: Qian Cai cai@lca.pw Cc: Kazuhito Hagio k-hagio@ab.jp.nec.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

mm/sparse.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/mm/sparse.c~mm-sparse-reset-sections-mem_map-when-fully-deactivated +++ a/mm/sparse.c @@ -789,7 +789,7 @@ static void section_deactivate(unsigned 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) _