Re: [PATCH 1/1] mm/hugetlb.c: teach follow_hugetlb_page() to handle FOLL_NOWAIT

[Peter Xu]

On Tue, Jan 08, 2019 at 09:02:03PM -0500, Andrea Arcangeli wrote:
> hugetlb needs the same fix as faultin_nopage (which was applied in
> 96312e61282ae3f6537a562625706498cbc75594) 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.
> 
> Fixes: ce53053ce378 ("kvm: switch get_user_page_nowait() to get_user_pages_unlocked()")
> Signed-off-by: Andrea Arcangeli <aarcange@xxxxxxxxxx>
> Tested-by: "Dr. David Alan Gilbert" <dgilbert@xxxxxxxxxx>
> Reported-by: "Dr. David Alan Gilbert" <dgilbert@xxxxxxxxxx>

FWIW:

Reviewed-by: Peter Xu <peterx@xxxxxxxxxx>

> ---
>  mm/hugetlb.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index e37efd5d8318..b3622d7888c8 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -4301,7 +4301,8 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
>  				break;
>  			}
>  			if (ret & VM_FAULT_RETRY) {
> -				if (nonblocking)
> +				if (nonblocking &&
> +				    !(fault_flags & FAULT_FLAG_RETRY_NOWAIT))
>  					*nonblocking = 0;
>  				*nr_pages = 0;
>  				/*

Regards,

-- 
Peter Xu