• Naoya Horiguchi's avatar
    hugetlbfs: add swap entry check in follow_hugetlb_page() · 9cc3a5bd
    Naoya Horiguchi authored
    With applying the previous patch "hugetlbfs: stop setting VM_DONTDUMP in
    initializing vma(VM_HUGETLB)" to reenable hugepage coredump, if a memory
    error happens on a hugepage and the affected processes try to access the
    error hugepage, we hit VM_BUG_ON(atomic_read(&page->_count) <= 0) in
    get_page().
    
    The reason for this bug is that coredump-related code doesn't recognise
    "hugepage hwpoison entry" with which a pmd entry is replaced when a memory
    error occurs on a hugepage.
    
    In other words, physical address information is stored in different bit
    layout between hugepage hwpoison entry and pmd entry, so
    follow_hugetlb_page() which is called in get_dump_page() returns a wrong
    page from a given address.
    
    The expected behavior is like this:
    
      absent   is_swap_pte   FOLL_DUMP   Expected behavior
      -------------------------------------------------------------------
       true     false         false       hugetlb_fault
       false    true          false       hugetlb_fault
       false    false         false       return page
       true     false         true        skip page (to avoid allocation)
       false    true          true        hugetlb_fault
       false    false         true        return page
    
    With this patch, we can call hugetlb_fault() and take proper actions (we
    wait for migration entries, fail with VM_FAULT_HWPOISON_LARGE for
    hwpoisoned entries,) and as the result we can dump all hugepages except
    for hwpoisoned ones.
    Signed-off-by: default avatarNaoya Horiguchi <n-horiguchi@ah.jp.nec.com>
    Cc: Rik van Riel <riel@redhat.com>
    Acked-by: default avatarMichal Hocko <mhocko@suse.cz>
    Cc: HATAYAMA Daisuke <d.hatayama@jp.fujitsu.com>
    Acked-by: default avatarKOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
    Acked-by: default avatarDavid Rientjes <rientjes@google.com>
    Cc: <stable@vger.kernel.org>	[2.6.34+?]
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    9cc3a5bd
hugetlb.c 82.9 KB