[004/118] mm/sparse.c: reset section's mem_map when fully deactivated

Commit Message

Andrew Morton Jan. 31, 2020, 6:11 a.m. UTC

From: Pingfan Liu <[e-mail]>
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/[e-mail]
Signed-off-by: Pingfan Liu <[e-mail]>
Acked-by: Michal Hocko <[e-mail]>
Acked-by: David Hildenbrand <[e-mail]>
Cc: Dan Williams <[e-mail]>
Cc: Oscar Salvador <[e-mail]>
Cc: Baoquan He <[e-mail]>
Cc: Qian Cai <[e-mail]>
Cc: Kazuhito Hagio <[e-mail]>
Cc: <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
---

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

Patch

--- 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)