linux-kernel - Re: [PATCH] mm/mmu_notifier: fix mmu_notifier_range

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Date:   Tue, 11 Dec 2018 15:19:09 -0500
From:   Jerome Glisse <jglisse@...hat.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Michal Hocko <mhocko@...e.com>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        David Rientjes <rientjes@...gle.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/mmu_notifier: fix mmu_notifier_range_init warning

On Tue, Dec 11, 2018 at 09:04:43PM +0100, Arnd Bergmann wrote:
> The macro version of mmu_notifier_range_init() for CONFIG_MMU_NOTIFIER=n
> does not evaluate all its arguments, leading to a warning in one case:
> 
> mm/migrate.c: In function 'migrate_vma_pages':
> mm/migrate.c:2711:20: error: unused variable 'mm' [-Werror=unused-variable]
>   struct mm_struct *mm = vma->vm_mm;
> 
> Pass down the 'mm' as into the inline function as well so gcc can
> see why the variable exists.
> 
> Fixes: 137d92bd73b1 ("mm/mmu_notifier: use structure for invalidate_range_start/end calls v2")

What about changing migrate.c (i actualy tried to do that everywhere in
the patchset but i missed that spot) So we avoid one useless variable on
such configuration:

diff --git a/mm/migrate.c b/mm/migrate.c
index f02bb4b22c1a..883fce631f47 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -2701,7 +2701,6 @@ static void migrate_vma_pages(struct migrate_vma *migrate)
 	const unsigned long npages = migrate->npages;
 	const unsigned long start = migrate->start;
 	struct vm_area_struct *vma = migrate->vma;
-	struct mm_struct *mm = vma->vm_mm;
 	struct mmu_notifier_range range;
 	unsigned long addr, i;
 	bool notified = false;
@@ -2724,8 +2723,8 @@ static void migrate_vma_pages(struct migrate_vma *migrate)
 			if (!notified) {
 				notified = true;
 
-				mmu_notifier_range_init(&range, mm, addr,
-							migrate->end,
+				mmu_notifier_range_init(&range, vma->vm_mm,
+							addr, migrate->end,
 							MMU_NOTIFY_CLEAR);
 				mmu_notifier_invalidate_range_start(&range);
 			}


> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
>  include/linux/mmu_notifier.h | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/mmu_notifier.h b/include/linux/mmu_notifier.h
> index 29f7b9670ba3..b13ea00ded5d 100644
> --- a/include/linux/mmu_notifier.h
> +++ b/include/linux/mmu_notifier.h
> @@ -476,6 +476,7 @@ struct mmu_notifier_range {
>  };
>  
>  static inline void _mmu_notifier_range_init(struct mmu_notifier_range *range,
> +					    struct mm_struct *mm,
>  					    unsigned long start,
>  					    unsigned long end)
>  {
> @@ -484,7 +485,7 @@ static inline void _mmu_notifier_range_init(struct mmu_notifier_range *range,
>  }
>  
>  #define mmu_notifier_range_init(range, mm, start, end, event) \
> -	_mmu_notifier_range_init(range, start, end)
> +	_mmu_notifier_range_init(range, mm, start, end)
>  
>  
>  static inline int mm_has_notifiers(struct mm_struct *mm)
> -- 
> 2.20.0
>