• Naoya Horiguchi's avatar
    mm: check __PG_HWPOISON separately from PAGE_FLAGS_CHECK_AT_* · f4c18e6f
    Naoya Horiguchi authored
    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>
    f4c18e6f
migrate.c 46.8 KB