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

0 files changed, 0 insertions, 0 deletions