From 1f503443e7df8dc8366608b4d810ce2d6669827c Mon Sep 17 00:00:00 2001 From: Pingfan Liu Date: Thu, 30 Jan 2020 22:11:10 -0800 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.com Signed-off-by: Pingfan Liu Acked-by: Michal Hocko Acked-by: David Hildenbrand Cc: Dan Williams Cc: Oscar Salvador Cc: Baoquan He Cc: Qian Cai Cc: Kazuhito Hagio Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/sparse.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/mm/sparse.c b/mm/sparse.c index 3822ecbd8a1f..3918fc3eaef1 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) -- cgit v1.2.3-59-g8ed1b