netdev - Re: [PATCH 04/10] mm: replace get_user_pages_locked() write/force parameters with gup

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Message-ID: <20161018125425.GD29967@quack2.suse.cz>
Date:   Tue, 18 Oct 2016 14:54:25 +0200
From:   Jan Kara <jack@...e.cz>
To:     Lorenzo Stoakes <lstoakes@...il.com>
Cc:     linux-mm@...ck.org, Linus Torvalds <torvalds@...ux-foundation.org>,
        Jan Kara <jack@...e.cz>, Hugh Dickins <hughd@...gle.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Rik van Riel <riel@...hat.com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Andrew Morton <akpm@...ux-foundation.org>,
        adi-buildroot-devel@...ts.sourceforge.net,
        ceph-devel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        intel-gfx@...ts.freedesktop.org, kvm@...r.kernel.org,
        linux-alpha@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-cris-kernel@...s.com, linux-fbdev@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-ia64@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-media@...r.kernel.org,
        linux-mips@...ux-mips.org, linux-rdma@...r.kernel.org,
        linux-s390@...r.kernel.org, linux-samsung-soc@...r.kernel.org,
        linux-scsi@...r.kernel.org, linux-security-module@...r.kernel.org,
        linux-sh@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        netdev@...r.kernel.org, sparclinux@...r.kernel.org, x86@...nel.org
Subject: Re: [PATCH 04/10] mm: replace get_user_pages_locked() write/force
 parameters with gup_flags

On Thu 13-10-16 01:20:14, Lorenzo Stoakes wrote:
> This patch removes the write and force parameters from get_user_pages_locked()
> and replaces them with a gup_flags parameter to make the use of FOLL_FORCE
> explicit in callers as use of this flag can result in surprising behaviour (and
> hence bugs) within the mm subsystem.
> 
> Signed-off-by: Lorenzo Stoakes <lstoakes@...il.com>
> ---
>  include/linux/mm.h |  2 +-
>  mm/frame_vector.c  |  8 +++++++-
>  mm/gup.c           | 12 +++---------
>  mm/nommu.c         |  5 ++++-
>  4 files changed, 15 insertions(+), 12 deletions(-)
> 
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 6adc4bc..27ab538 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -1282,7 +1282,7 @@ long get_user_pages(unsigned long start, unsigned long nr_pages,
>  			    int write, int force, struct page **pages,
>  			    struct vm_area_struct **vmas);
>  long get_user_pages_locked(unsigned long start, unsigned long nr_pages,
> -		    int write, int force, struct page **pages, int *locked);
> +		    unsigned int gup_flags, struct page **pages, int *locked);

Hum, the prototype is inconsistent with e.g. __get_user_pages_unlocked()
where gup_flags come after **pages argument. Actually it makes more sense
to have it before **pages so that input arguments come first and output
arguments second but I don't care that much. But it definitely should be
consistent...

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR