Re: [Intel-gfx] [PATCH 04/10] mm: replace get_user_pages_locked() write/force parameters with gup_flags

[Jan Kara]

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 

After our discussion the patch looks good to me. You can add:

Reviewed-by: Jan Kara 

Honza
-- 
Jan Kara 
SUSE Labs, CR
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Re: [Intel-gfx] [PATCH 04/10] mm: replace get_user_pages_locked() write/force parameters with gup_flags

[Jan Kara]

On Tue 18-10-16 14:56:09, Lorenzo Stoakes wrote:
> On Tue, Oct 18, 2016 at 02:54:25PM +0200, Jan Kara wrote:
> > > @@ -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...
> 
> It was difficult to decide quite how to arrange parameters as there was
> inconsitency with regards to parameter ordering already - for example
> __get_user_pages() places its flags argument before pages whereas, as you 
> note,
> __get_user_pages_unlocked() puts them afterwards.
> 
> I ended up compromising by trying to match the existing ordering of the 
> function
> as much as I could by replacing write, force pairs with gup_flags in the same
> location (with the exception of get_user_pages_unlocked() which I felt should
> match __get_user_pages_unlocked() in signature) or if there was already a
> gup_flags parameter as in the case of __get_user_pages_unlocked() I simply
> removed the write, force pair and left the flags as the last parameter.
> 
> I am happy to rearrange parameters as needed, however I am not sure if it'd be
> worthwhile for me to do so (I am keen to try to avoid adding too much noise 
> here
> :)
> 
> If we were to rearrange parameters for consistency I'd suggest adjusting
> __get_user_pages_unlocked() to put gup_flags before pages and do the same with
> get_user_pages_unlocked(), let me know what you think.

Yeah, ok. If the inconsistency is already there, just leave it for now.

Honza
-- 
Jan Kara 
SUSE Labs, CR
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Re: [Intel-gfx] [PATCH 04/10] mm: replace get_user_pages_locked() write/force parameters with gup_flags

[Lorenzo Stoakes]

On Tue, Oct 18, 2016 at 02:54:25PM +0200, Jan Kara wrote:
> > @@ -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...

It was difficult to decide quite how to arrange parameters as there was
inconsitency with regards to parameter ordering already - for example
__get_user_pages() places its flags argument before pages whereas, as you note,
__get_user_pages_unlocked() puts them afterwards.

I ended up compromising by trying to match the existing ordering of the function
as much as I could by replacing write, force pairs with gup_flags in the same
location (with the exception of get_user_pages_unlocked() which I felt should
match __get_user_pages_unlocked() in signature) or if there was already a
gup_flags parameter as in the case of __get_user_pages_unlocked() I simply
removed the write, force pair and left the flags as the last parameter.

I am happy to rearrange parameters as needed, however I am not sure if it'd be
worthwhile for me to do so (I am keen to try to avoid adding too much noise here
:)

If we were to rearrange parameters for consistency I'd suggest adjusting
__get_user_pages_unlocked() to put gup_flags before pages and do the same with
get_user_pages_unlocked(), let me know what you think.
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Re: [Intel-gfx] [PATCH 04/10] mm: replace get_user_pages_locked() write/force parameters with gup_flags

[Jan Kara]

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 
> ---
>  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 
SUSE Labs, CR
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[Intel-gfx] [PATCH 04/10] mm: replace get_user_pages_locked() write/force parameters with gup_flags

[Lorenzo Stoakes]

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 
---
 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);
 long __get_user_pages_unlocked(struct task_struct *tsk, struct mm_struct *mm,
   unsigned long start, unsigned long nr_pages,
   struct page **pages, unsigned int gup_flags);
diff --git a/mm/frame_vector.c b/mm/frame_vector.c
index 381bb07..81b6749 100644
--- a/mm/frame_vector.c
+++ b/mm/frame_vector.c
@@ -41,10 +41,16 @@ int get_vaddr_frames(unsigned long start, unsigned int 
nr_frames,
int ret = 0;
int err;
int locked;
+   unsigned int gup_flags = 0;
 
if (nr_frames == 0)
return 0;
 
+   if (write)
+   gup_flags |= FOLL_WRITE;
+   if (force)
+   gup_flags |= FOLL_FORCE;
+
if (WARN_ON_ONCE(nr_frames > vec->nr_allocated))
nr_frames = vec->nr_allocated;
 
@@ -59,7 +65,7 @@ int get_vaddr_frames(unsigned long start, unsigned int 
nr_frames,
vec->got_ref = true;
vec->is_pfns = false;
ret = get_user_pages_locked(start, nr_frames,
-   write, force, (struct page **)(vec->ptrs), );
+   gup_flags, (struct page **)(vec->ptrs), );
goto out;
}
 
diff --git a/mm/gup.c b/mm/gup.c
index cfcb014..7a0d033 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -838,18 +838,12 @@ static __always_inline long 
__get_user_pages_locked(struct task_struct *tsk,
  *  up_read(>mmap_sem);
  */
 long get_user_pages_locked(unsigned long start, unsigned long nr_pages,
-  int write, int force, struct page **pages,
+  unsigned int gup_flags, struct page **pages,
   int *locked)
 {
-   unsigned int flags = FOLL_TOUCH;
-
-   if (write)
-   flags |= FOLL_WRITE;
-   if (force)
-   flags |= FOLL_FORCE;
-
return __get_user_pages_locked(current, current->mm, start, nr_pages,
-  pages, NULL, locked, true, flags);
+  pages, NULL, locked, true,
+  gup_flags | FOLL_TOUCH);
 }
 EXPORT_SYMBOL(get_user_pages_locked);
 
diff --git a/mm/nommu.c b/mm/nommu.c
index 7e27add..842cfdd 100644
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -176,9 +176,12 @@ long get_user_pages(unsigned long start, unsigned long 
nr_pages,
 EXPORT_SYMBOL(get_user_pages);
 
 long get_user_pages_locked(unsigned long start, unsigned long nr_pages,
-   int write, int force, struct page **pages,
+   unsigned int gup_flags, struct page **pages,
int *locked)
 {
+   int write = gup_flags & FOLL_WRITE;
+   int force = gup_flags & FOLL_FORCE;
+
return get_user_pages(start, nr_pages, write, force, pages, NULL);
 }
 EXPORT_SYMBOL(get_user_pages_locked);
-- 
2.10.0

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