Re: [PATCH 5/8] mm/gup: add FOLL_UNLOCK

[Mike Rapoport <rppt@kernel.org>]

On Tue, Jan 17, 2023 at 11:58:36AM -0400, Jason Gunthorpe wrote:
> Setting FOLL_UNLOCK allows GUP to lock/unlock the mmap lock on its own. It
> is a more explicit replacement for locked != NULL. This clears the way for
> passing in locked = 1, without intending that the lock can be unlocked.
> 
> Set the flag in all cases where it is used, eg locked is present in the
> external interface or locked is used internally with locked = 0.
> 
> Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
> ---
>  include/linux/mm.h |  1 +
>  mm/gup.c           | 31 +++++++++++++++++++------------
>  2 files changed, 20 insertions(+), 12 deletions(-)
> 
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index f3f196e4d66d6f..7496a5c8acede1 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -3089,6 +3089,7 @@ struct page *follow_page(struct vm_area_struct *vma, unsigned long address,
>  #define FOLL_FAST_ONLY	0x80000	/* gup_fast: prevent fall-back to slow gup */
>  #define FOLL_PCI_P2PDMA	0x100000 /* allow returning PCI P2PDMA pages */
>  #define FOLL_INTERRUPTIBLE  0x200000 /* allow interrupts from generic signals */
> +#define FOLL_UNLOCK	0x400000 /* allow unlocking the mmap lock */

Please add a comment that this is an internal flag.
  
>  /*
>   * FOLL_PIN and FOLL_LONGTERM may be used in various combinations with each

-- 
Sincerely yours,
Mike.