From: Andrea Arcangeli <aarcange@xxxxxxxxxx> Subject: userfaultfd: non-cooperative: avoid MADV_DONTNEED race condition MADV_DONTNEED must be notified to userland before the pages are zapped. This allows userland to immediately stop adding pages to the userfaultfd ranges before the pages are actually zapped or there could be non-zeropage leftovers as result of concurrent UFFDIO_COPY run in between zap_page_range and madvise_userfault_dontneed (both MADV_DONTNEED and UFFDIO_COPY runs under the mmap_sem for reading, so they can run concurrently). Link: http://lkml.kernel.org/r/20161216144821.5183-15-aarcange@xxxxxxxxxx Signed-off-by: Andrea Arcangeli <aarcange@xxxxxxxxxx> Cc: "Dr. David Alan Gilbert" <dgilbert@xxxxxxxxxx> Cc: Hillf Danton <hillf.zj@xxxxxxxxxxxxxxx> Cc: Michael Rapoport <RAPOPORT@xxxxxxxxxx> Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx> Cc: Mike Rapoport <rppt@xxxxxxxxxxxxxxxxxx> Cc: Pavel Emelyanov <xemul@xxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/madvise.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff -puN mm/madvise.c~userfaultfd-non-cooperative-avoid-madv_dontneed-race-condition mm/madvise.c --- a/mm/madvise.c~userfaultfd-non-cooperative-avoid-madv_dontneed-race-condition +++ a/mm/madvise.c @@ -477,8 +477,8 @@ static long madvise_dontneed(struct vm_a if (vma->vm_flags & (VM_LOCKED|VM_HUGETLB|VM_PFNMAP)) return -EINVAL; - zap_page_range(vma, start, end - start, NULL); madvise_userfault_dontneed(vma, prev, start, end); + zap_page_range(vma, start, end - start, NULL); return 0; } _ -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
