Re: [PATCHv6 1/3] mm/gup: rename nr as nr_pinned in get_user_pages_fast()

[John Hubbard <jhubbard@nvidia.com>]

On 3/15/20 9:34 PM, Pingfan Liu wrote:
> To better reflect the held state of pages and make code
> self-explaining, rename nr as nr_pinned.
> 
> Signed-off-by: Pingfan Liu <kernelfans@gmail.com> Cc: Ira Weiny
> <ira.weiny@intel.com> Cc: Andrew Morton <akpm@linux-foundation.org> 
> Cc: Mike Rapoport <rppt@linux.ibm.com> Cc: Dan Williams
> <dan.j.williams@intel.com> Cc: Matthew Wilcox <willy@infradead.org> 
> Cc: John Hubbard <jhubbard@nvidia.com> Cc: "Aneesh Kumar K.V"
> <aneesh.kumar@linux.ibm.com> Cc: Christoph Hellwig
> <hch@infradead.org> Cc: Shuah Khan <shuah@kernel.org> To:
> linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org --- mm/gup.c | 20
> ++++++++++---------- 1 file changed, 10 insertions(+), 10
> deletions(-)
> 

Hi Pingfan,

This is correct as far as it goes, but it doesn't go quite far enough. This should
at least should cover the other caller of gup_pgd_range().

Background: There are two internal-to-gup.c entry points to gup fast:
internal_get_user_pages_fast(), and __get_user_pages_fast(). Quite commonly when
submitting fixes to one of these functions, the other is overlooked, as happened
here.

Here's a diff on top of your patch, that I think should be squashed into your patch:

diff --git a/mm/gup.c b/mm/gup.c
index d0c0d084e792..56052b73abc3 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -2676,7 +2676,7 @@ int __get_user_pages_fast(unsigned long start, int nr_pages, int write,
  {
  	unsigned long len, end;
  	unsigned long flags;
-	int nr = 0;
+	int nr_pinned = 0;
  	/*
  	 * Internally (within mm/gup.c), gup fast variants must set FOLL_GET,
  	 * because gup fast is always a "pin with a +1 page refcount" request.
@@ -2710,11 +2710,11 @@ int __get_user_pages_fast(unsigned long start, int nr_pages, int write,
  	if (IS_ENABLED(CONFIG_HAVE_FAST_GUP) &&
  	    gup_fast_permitted(start, end)) {
  		local_irq_save(flags);
-		gup_pgd_range(start, end, gup_flags, pages, &nr);
+		gup_pgd_range(start, end, gup_flags, pages, &nr_pinned);
  		local_irq_restore(flags);
  	}
  
-	return nr;
+	return nr_pinned;
  }
  EXPORT_SYMBOL_GPL(__get_user_pages_fast);
  

With that applied, you can add:

     Reviewed-by: John Hubbard <jhubbard@nvidia.com>


thanks,
-- 
John Hubbard
NVIDIA

> diff --git a/mm/gup.c b/mm/gup.c index e8aaa40..9df77b1 100644 ---
> a/mm/gup.c +++ b/mm/gup.c @@ -2735,7 +2735,7 @@ static int
> internal_get_user_pages_fast(unsigned long start, int nr_pages, 
> struct page **pages) { unsigned long addr, len, end; -	int nr = 0,
> ret = 0; +	int nr_pinned = 0, ret = 0;
> 
> if (WARN_ON_ONCE(gup_flags & ~(FOLL_WRITE | FOLL_LONGTERM | 
> FOLL_FORCE | FOLL_PIN | FOLL_GET))) @@ -2754,25 +2754,25 @@ static
> int internal_get_user_pages_fast(unsigned long start, int nr_pages, 
> if (IS_ENABLED(CONFIG_HAVE_FAST_GUP) && gup_fast_permitted(start,
> end)) { local_irq_disable(); -		gup_pgd_range(addr, end, gup_flags,
> pages, &nr); +		gup_pgd_range(addr, end, gup_flags, pages,
> &nr_pinned); local_irq_enable(); -		ret = nr; +		ret = nr_pinned; }
> 
> -	if (nr < nr_pages) { +	if (nr_pinned < nr_pages) { /* Try to get
> the remaining pages with get_user_pages */ -		start += nr <<
> PAGE_SHIFT; -		pages += nr; +		start += nr_pinned << PAGE_SHIFT; +
> pages += nr_pinned;
> 
> -		ret = __gup_longterm_unlocked(start, nr_pages - nr, +		ret =
> __gup_longterm_unlocked(start, nr_pages - nr_pinned, gup_flags,
> pages);
> 
> /* Have to be a bit careful with return values */ -		if (nr > 0) { +
> if (nr_pinned > 0) { if (ret < 0) -				ret = nr; +				ret =
> nr_pinned; else -				ret += nr; +				ret += nr_pinned; } }
> 
> -- 2.7.5
>