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Date: Fri, 31 Jul 2015 06:46:13 +0000
From: Naoya Horiguchi <n-horiguchi@...jp.nec.com>
To: Andrew Morton <akpm@...ux-foundation.org>
CC: Andi Kleen <andi@...stfloor.org>, Dean Nelson <dnelson@...hat.com>,
"Tony Luck" <tony.luck@...el.com>,
"Kirill A. Shutemov" <kirill@...temov.name>,
"Hugh Dickins" <hughd@...gle.com>,
"linux-mm@...ck.org" <linux-mm@...ck.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"Naoya Horiguchi" <nao.horiguchi@...il.com>,
Naoya Horiguchi <n-horiguchi@...jp.nec.com>
Subject: [PATCH v2 4/5] mm: check __PG_HWPOISON separately from
PAGE_FLAGS_CHECK_AT_*
The race condition addressed in commit add05cecef80 ("mm: soft-offline: don't
free target page in successful page migration") was not closed completely,
because that can happen not only for soft-offline, but also for hard-offline.
Consider that a slab page is about to be freed into buddy pool, and then an
uncorrected memory error hits the page just after entering __free_one_page(),
then VM_BUG_ON_PAGE(page->flags & PAGE_FLAGS_CHECK_AT_PREP) is triggered,
despite the fact that it's not necessary because the data on the affected
page is not consumed.
To solve it, this patch drops __PG_HWPOISON from page flag checks at
allocation/free time. I think it's justified because __PG_HWPOISON flags is
defined to prevent the page from being reused, and setting it outside the
page's alloc-free cycle is a designed behavior (not a bug.)
For recent months, I was annoyed about BUG_ON when soft-offlined page remains
on lru cache list for a while, which is avoided by calling put_page() instead
of putback_lru_page() in page migration's success path. This means that this
patch reverts a major change from commit add05cecef80 about the new refcounting
rule of soft-offlined pages, so "reuse window" revives. This will be closed
by a subsequent patch.
Signed-off-by: Naoya Horiguchi <n-horiguchi@...jp.nec.com>
---
v1 -> v2:
- call put_page() when migration succeeded in reason == MR_MEMORY_FAILURE
- refrain from reviving "reuse prevention" by MIGRATE_ISOLATE flag
---
include/linux/page-flags.h | 10 +++++++---
mm/huge_memory.c | 7 +------
mm/migrate.c | 5 ++++-
mm/page_alloc.c | 4 ++++
4 files changed, 16 insertions(+), 10 deletions(-)
diff --git v4.2-rc4.orig/include/linux/page-flags.h v4.2-rc4/include/linux/page-flags.h
index f34e040b34e9..41c93844fb1d 100644
--- v4.2-rc4.orig/include/linux/page-flags.h
+++ v4.2-rc4/include/linux/page-flags.h
@@ -631,15 +631,19 @@ static inline void ClearPageSlabPfmemalloc(struct page *page)
1 << PG_private | 1 << PG_private_2 | \
1 << PG_writeback | 1 << PG_reserved | \
1 << PG_slab | 1 << PG_swapcache | 1 << PG_active | \
- 1 << PG_unevictable | __PG_MLOCKED | __PG_HWPOISON | \
+ 1 << PG_unevictable | __PG_MLOCKED | \
__PG_COMPOUND_LOCK)
/*
* Flags checked when a page is prepped for return by the page allocator.
- * Pages being prepped should not have any flags set. It they are set,
+ * Pages being prepped should not have these flags set. It they are set,
* there has been a kernel bug or struct page corruption.
+ *
+ * __PG_HWPOISON is exceptional because it needs to be kept beyond page's
+ * alloc-free cycle to prevent from reusing the page.
*/
-#define PAGE_FLAGS_CHECK_AT_PREP ((1 << NR_PAGEFLAGS) - 1)
+#define PAGE_FLAGS_CHECK_AT_PREP \
+ (((1 << NR_PAGEFLAGS) - 1) & ~__PG_HWPOISON)
#define PAGE_FLAGS_PRIVATE \
(1 << PG_private | 1 << PG_private_2)
diff --git v4.2-rc4.orig/mm/huge_memory.c v4.2-rc4/mm/huge_memory.c
index c107094f79ba..097c7a4bfbd9 100644
--- v4.2-rc4.orig/mm/huge_memory.c
+++ v4.2-rc4/mm/huge_memory.c
@@ -1676,12 +1676,7 @@ static void __split_huge_page_refcount(struct page *page,
/* after clearing PageTail the gup refcount can be released */
smp_mb__after_atomic();
- /*
- * retain hwpoison flag of the poisoned tail page:
- * fix for the unsuitable process killed on Guest Machine(KVM)
- * by the memory-failure.
- */
- page_tail->flags &= ~PAGE_FLAGS_CHECK_AT_PREP | __PG_HWPOISON;
+ page_tail->flags &= ~PAGE_FLAGS_CHECK_AT_PREP;
page_tail->flags |= (page->flags &
((1L << PG_referenced) |
(1L << PG_swapbacked) |
diff --git v4.2-rc4.orig/mm/migrate.c v4.2-rc4/mm/migrate.c
index ee401e4e5ef1..f2415be7d93b 100644
--- v4.2-rc4.orig/mm/migrate.c
+++ v4.2-rc4/mm/migrate.c
@@ -950,7 +950,10 @@ static ICE_noinline int unmap_and_move(new_page_t get_new_page,
list_del(&page->lru);
dec_zone_page_state(page, NR_ISOLATED_ANON +
page_is_file_cache(page));
- if (reason != MR_MEMORY_FAILURE)
+ /* Soft-offlined page shouldn't go through lru cache list */
+ if (reason == MR_MEMORY_FAILURE)
+ put_page(page);
+ else
putback_lru_page(page);
}
diff --git v4.2-rc4.orig/mm/page_alloc.c v4.2-rc4/mm/page_alloc.c
index ef19f22b2b7d..775c254648f7 100644
--- v4.2-rc4.orig/mm/page_alloc.c
+++ v4.2-rc4/mm/page_alloc.c
@@ -1285,6 +1285,10 @@ static inline int check_new_page(struct page *page)
bad_reason = "non-NULL mapping";
if (unlikely(atomic_read(&page->_count) != 0))
bad_reason = "nonzero _count";
+ if (unlikely(page->flags & __PG_HWPOISON)) {
+ bad_reason = "HWPoisoned (hardware-corrupted)";
+ bad_flags = __PG_HWPOISON;
+ }
if (unlikely(page->flags & PAGE_FLAGS_CHECK_AT_PREP)) {
bad_reason = "PAGE_FLAGS_CHECK_AT_PREP flag set";
bad_flags = PAGE_FLAGS_CHECK_AT_PREP;
--
2.4.3
--
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