From: Pingfan Liu <kernelfans@xxxxxxxxx>
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@xxxxxxxxx
Signed-off-by: Pingfan Liu <kernelfans@xxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
Acked-by: David Hildenbrand <david@xxxxxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: Oscar Salvador <osalvador@xxxxxxx>
Cc: Baoquan He <bhe@xxxxxxxxxx>
Cc: Qian Cai <cai@xxxxxx>
Cc: Kazuhito Hagio <k-hagio@xxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
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)
_
