[patch 01/15] mm: skip HWPoisoned pages when onlining pages

[akpm@linux-foundation.org]

From: Laurent Dufour <ldufour@linux.vnet.ibm.com>
Subject: mm: skip HWPoisoned pages when onlining pages

b023f46813cd ("memory-hotplug: skip HWPoisoned page when offlining pages")
skipped the HWPoisoned pages when offlining pages, but this should be
skipped when onlining the pages too.

n-horiguchi@ah.jp.nec.com said:

: If I read correctly, to "skip HWPoiosned page" in commit b023f46813cd
: means that we skip the page status check for hwpoisoned pages *not* to
: prevent memory offlining for memblocks with hwpoisoned pages.  That
: means that hwpoisoned pages can be offlined.
: 
: And another reason to clear PageReserved is that we could reuse the
: hwpoisoned page after onlining back with replacing the broken DIMM.  In
: this usecase, we first do unpoisoning to clear PageHWPoison, but it
: doesn't work if PageReserved is set.  My simple testing shows the BUG
: below in unpoisoning (without the ClearPageReserved):
: 
:   Unpoison: Software-unpoisoned page 0x18000
:   BUG: Bad page state in process page-types  pfn:18000
:   page:ffffda5440600000 count:0 mapcount:0 mapping:          (null) index:0x70006b599
:   flags: 0x1fffc00004081a(error|uptodate|dirty|reserved|swapbacked)
:   raw: 001fffc00004081a 0000000000000000 000000070006b599 00000000ffffffff
:   raw: dead000000000100 dead000000000200 0000000000000000 0000000000000000
:   page dumped because: PAGE_FLAGS_CHECK_AT_FREE flag(s) set
:   bad because of flags: 0x800(reserved)

Link: http://lkml.kernel.org/r/1493130472-22843-3-git-send-email-ldufour@linux.vnet.ibm.com
Signed-off-by: Laurent Dufour <ldufour@linux.vnet.ibm.com>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Andrey Vagin <avagin@openvz.org>
Cc: Glauber Costa <glommer@openvz.org>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Cc: Balbir Singh <bsingharora@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/memory_hotplug.c |    4 ++++
 1 file changed, 4 insertions(+)

diff -puN mm/memory_hotplug.c~mm-skip-hwpoisoned-pages-when-onlining-pages mm/memory_hotplug.c
--- a/mm/memory_hotplug.c~mm-skip-hwpoisoned-pages-when-onlining-pages
+++ a/mm/memory_hotplug.c
@@ -696,6 +696,10 @@ static int online_pages_range(unsigned l
 	if (PageReserved(pfn_to_page(start_pfn)))
 		for (i = 0; i < nr_pages; i++) {
 			page = pfn_to_page(start_pfn + i);
+			if (PageHWPoison(page)) {
+				ClearPageReserved(page);
+				continue;
+			}
 			(*online_page_callback)(page);
 			onlined_pages++;
 		}
_

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