linux-kernel - Re: [PATCH v3 02/12] mm/gup: split get_user_pages

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Message-ID: <20200203142006.GD18591@quack2.suse.cz>
Date:   Mon, 3 Feb 2020 15:20:06 +0100
From:   Jan Kara <jack@...e.cz>
To:     John Hubbard <jhubbard@...dia.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Christoph Hellwig <hch@...radead.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Dave Chinner <david@...morbit.com>,
        Ira Weiny <ira.weiny@...el.com>, Jan Kara <jack@...e.cz>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Jonathan Corbet <corbet@....net>,
        Jérôme Glisse <jglisse@...hat.com>,
        "Kirill A . Shutemov" <kirill@...temov.name>,
        Michal Hocko <mhocko@...e.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Shuah Khan <shuah@...nel.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Matthew Wilcox <willy@...radead.org>,
        linux-doc@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-kselftest@...r.kernel.org, linux-rdma@...r.kernel.org,
        linux-mm@...ck.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 02/12] mm/gup: split get_user_pages_remote() into two
 routines

On Fri 31-01-20 19:40:19, John Hubbard wrote:
> An upcoming patch requires reusing the implementation of
> get_user_pages_remote(). Split up get_user_pages_remote() into an outer
> routine that checks flags, and an implementation routine that will be
> reused. This makes subsequent changes much easier to understand.
> 
> There should be no change in behavior due to this patch.
> 
> Signed-off-by: John Hubbard <jhubbard@...dia.com>

Looks good to me. You can add:

Reviewed-by: Jan Kara <jack@...e.cz>

								Honza

> ---
>  mm/gup.c | 56 +++++++++++++++++++++++++++++++++-----------------------
>  1 file changed, 33 insertions(+), 23 deletions(-)
> 
> diff --git a/mm/gup.c b/mm/gup.c
> index e13f4d211475..228aa7059018 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -1557,6 +1557,37 @@ static __always_inline long __gup_longterm_locked(struct task_struct *tsk,
>  }
>  #endif /* CONFIG_FS_DAX || CONFIG_CMA */
>  
> +#ifdef CONFIG_MMU
> +static long __get_user_pages_remote(struct task_struct *tsk,
> +				    struct mm_struct *mm,
> +				    unsigned long start, unsigned long nr_pages,
> +				    unsigned int gup_flags, struct page **pages,
> +				    struct vm_area_struct **vmas, int *locked)
> +{
> +	/*
> +	 * Parts of FOLL_LONGTERM behavior are incompatible with
> +	 * FAULT_FLAG_ALLOW_RETRY because of the FS DAX check requirement on
> +	 * vmas. However, this only comes up if locked is set, and there are
> +	 * callers that do request FOLL_LONGTERM, but do not set locked. So,
> +	 * allow what we can.
> +	 */
> +	if (gup_flags & FOLL_LONGTERM) {
> +		if (WARN_ON_ONCE(locked))
> +			return -EINVAL;
> +		/*
> +		 * This will check the vmas (even if our vmas arg is NULL)
> +		 * and return -ENOTSUPP if DAX isn't allowed in this case:
> +		 */
> +		return __gup_longterm_locked(tsk, mm, start, nr_pages, pages,
> +					     vmas, gup_flags | FOLL_TOUCH |
> +					     FOLL_REMOTE);
> +	}
> +
> +	return __get_user_pages_locked(tsk, mm, start, nr_pages, pages, vmas,
> +				       locked,
> +				       gup_flags | FOLL_TOUCH | FOLL_REMOTE);
> +}
> +
>  /*
>   * get_user_pages_remote() - pin user pages in memory
>   * @tsk:	the task_struct to use for page fault accounting, or
> @@ -1619,7 +1650,6 @@ static __always_inline long __gup_longterm_locked(struct task_struct *tsk,
>   * should use get_user_pages because it cannot pass
>   * FAULT_FLAG_ALLOW_RETRY to handle_mm_fault.
>   */
> -#ifdef CONFIG_MMU
>  long get_user_pages_remote(struct task_struct *tsk, struct mm_struct *mm,
>  		unsigned long start, unsigned long nr_pages,
>  		unsigned int gup_flags, struct page **pages,
> @@ -1632,28 +1662,8 @@ long get_user_pages_remote(struct task_struct *tsk, struct mm_struct *mm,
>  	if (WARN_ON_ONCE(gup_flags & FOLL_PIN))
>  		return -EINVAL;
>  
> -	/*
> -	 * Parts of FOLL_LONGTERM behavior are incompatible with
> -	 * FAULT_FLAG_ALLOW_RETRY because of the FS DAX check requirement on
> -	 * vmas. However, this only comes up if locked is set, and there are
> -	 * callers that do request FOLL_LONGTERM, but do not set locked. So,
> -	 * allow what we can.
> -	 */
> -	if (gup_flags & FOLL_LONGTERM) {
> -		if (WARN_ON_ONCE(locked))
> -			return -EINVAL;
> -		/*
> -		 * This will check the vmas (even if our vmas arg is NULL)
> -		 * and return -ENOTSUPP if DAX isn't allowed in this case:
> -		 */
> -		return __gup_longterm_locked(tsk, mm, start, nr_pages, pages,
> -					     vmas, gup_flags | FOLL_TOUCH |
> -					     FOLL_REMOTE);
> -	}
> -
> -	return __get_user_pages_locked(tsk, mm, start, nr_pages, pages, vmas,
> -				       locked,
> -				       gup_flags | FOLL_TOUCH | FOLL_REMOTE);
> +	return __get_user_pages_remote(tsk, mm, start, nr_pages, gup_flags,
> +				       pages, vmas, locked);
>  }
>  EXPORT_SYMBOL(get_user_pages_remote);
>  
> -- 
> 2.25.0
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR