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Commit f4c18e6f authored by Naoya Horiguchi's avatar Naoya Horiguchi Committed by Linus Torvalds
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mm: check __PG_HWPOISON separately from PAGE_FLAGS_CHECK_AT_* 



The race condition addressed in commit add05cec ("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
add05cec about the new refcounting rule of soft-offlined pages, so
"reuse window" revives.  This will be closed by a subsequent patch.

Signed-off-by: default avatarNaoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Dean Nelson <dnelson@redhat.com>
Cc: Tony Luck <tony.luck@intel.com>
Cc: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: Hugh Dickins <hughd@google.com>
Cc: David Rientjes <rientjes@google.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 98ed2b00

include/linux/page-flags.h

+7 −3
Original line number Diff line number Diff line
@@ -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)

mm/huge_memory.c

+1 −6
Original line number Diff line number Diff line
@@ -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) |

mm/migrate.c

+4 −1
Original line number Diff line number Diff line
@@ -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);

	}

mm/page_alloc.c

+4 −0
Original line number Diff line number Diff line
@@ -1296,6 +1296,10 @@ 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;