linux-kernel - [PATCH 5.5 055/367] mm/sparse.c: reset sections mem

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Date:   Mon, 10 Feb 2020 04:29:28 -0800
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Pingfan Liu <kernelfans@...il.com>,
        Michal Hocko <mhocko@...e.com>,
        David Hildenbrand <david@...hat.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Oscar Salvador <osalvador@...e.de>,
        Baoquan He <bhe@...hat.com>, Qian Cai <cai@....pw>,
        Kazuhito Hagio <k-hagio@...jp.nec.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH 5.5 055/367] mm/sparse.c: reset sections mem_map when fully deactivated

From: Pingfan Liu <kernelfans@...il.com>

commit 1f503443e7df8dc8366608b4d810ce2d6669827c upstream.

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 <kernelfans@...il.com>
Acked-by: Michal Hocko <mhocko@...e.com>
Acked-by: David Hildenbrand <david@...hat.com>
Cc: Dan Williams <dan.j.williams@...el.com>
Cc: Oscar Salvador <osalvador@...e.de>
Cc: Baoquan He <bhe@...hat.com>
Cc: Qian Cai <cai@....pw>
Cc: Kazuhito Hagio <k-hagio@...jp.nec.com>
Cc: <stable@...r.kernel.org>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

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

--- a/mm/sparse.c
+++ b/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)