• Daniel Jordan's avatar
    mm/hugetlb.c: __get_user_pages ignores certain follow_hugetlb_page errors · 2be7cfed
    Daniel Jordan authored
    Commit 9a291a7c ("mm/hugetlb: report -EHWPOISON not -EFAULT when
    FOLL_HWPOISON is specified") causes __get_user_pages to ignore certain
    errors from follow_hugetlb_page.  After such error, __get_user_pages
    subsequently calls faultin_page on the same VMA and start address that
    follow_hugetlb_page failed on instead of returning the error immediately
    as it should.
    
    In follow_hugetlb_page, when hugetlb_fault returns a value covered under
    VM_FAULT_ERROR, follow_hugetlb_page returns it without setting nr_pages
    to 0 as __get_user_pages expects in this case, which causes the
    following to happen in __get_user_pages: the "while (nr_pages)" check
    succeeds, we skip the "if (!vma..." check because we got a VMA the last
    time around, we find no page with follow_page_mask, and we call
    faultin_page, which calls hugetlb_fault for the second time.
    
    This issue also slightly changes how __get_user_pages works.  Before, it
    only returned error if it had made no progress (i = 0).  But now,
    follow_hugetlb_page can clobber "i" with an error code since its new
    return path doesn't check for progress.  So if "i" is nonzero before a
    failing call to follow_hugetlb_page, that indication of progress is lost
    and __get_user_pages can return error even if some pages were
    successfully pinned.
    
    To fix this, change follow_hugetlb_page so that it updates nr_pages,
    allowing __get_user_pages to fail immediately and restoring the "error
    only if no progress" behavior to __get_user_pages.
    
    Tested that __get_user_pages returns when expected on error from
    hugetlb_fault in follow_hugetlb_page.
    
    Fixes: 9a291a7c ("mm/hugetlb: report -EHWPOISON not -EFAULT when FOLL_HWPOISON is specified")
    Link: http://lkml.kernel.org/r/1500406795-58462-1-git-send-email-daniel.m.jordan@oracle.comSigned-off-by: default avatarDaniel Jordan <daniel.m.jordan@oracle.com>
    Acked-by: default avatarPunit Agrawal <punit.agrawal@arm.com>
    Cc: Andrea Arcangeli <aarcange@redhat.com>
    Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
    Cc: Gerald Schaefer <gerald.schaefer@de.ibm.com>
    Cc: James Morse <james.morse@arm.com>
    Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
    Cc: Michal Hocko <mhocko@suse.com>
    Cc: Mike Kravetz <mike.kravetz@oracle.com>
    Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
    Cc: zhong jiang <zhongjiang@huawei.com>
    Cc: <stable@vger.kernel.org>	[4.12.x]
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    2be7cfed
hugetlb.c 127 KB