From: Andrea Arcangeli aarcange@redhat.com Subject: mm/hugetlb.c: teach follow_hugetlb_page() to handle FOLL_NOWAIT

hugetlb needs the same fix as faultin_nopage (which was applied in 96312e61282ae ("mm/gup.c: teach get_user_pages_unlocked to handle FOLL_NOWAIT")) or KVM hangs because it thinks the mmap_sem was already released by hugetlb_fault() if it returned VM_FAULT_RETRY, but it wasn't in the FOLL_NOWAIT case.

Link: http://lkml.kernel.org/r/20190109020203.26669-2-aarcange@redhat.com Fixes: ce53053ce378 ("kvm: switch get_user_page_nowait() to get_user_pages_unlocked()") Signed-off-by: Andrea Arcangeli aarcange@redhat.com Tested-by: "Dr. David Alan Gilbert" dgilbert@redhat.com Reported-by: "Dr. David Alan Gilbert" dgilbert@redhat.com Reviewed-by: Mike Kravetz mike.kravetz@oracle.com Reviewed-by: Peter Xu peterx@redhat.com Cc: Mike Rapoport rppt@linux.vnet.ibm.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

mm/hugetlb.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/mm/hugetlb.c~mm-hugetlbc-teach-follow_hugetlb_page-to-handle-foll_nowait +++ a/mm/hugetlb.c @@ -4268,7 +4268,8 @@ long follow_hugetlb_page(struct mm_struc break; } if (ret & VM_FAULT_RETRY) { - if (nonblocking) + if (nonblocking && + !(fault_flags & FAULT_FLAG_RETRY_NOWAIT)) *nonblocking = 0; *nr_pages = 0; /* _