linux-kernel - Re: [PATCH] mm/vma: small VMA lock cleanups

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Message-ID: <eb40bf3f-dc12-4ed5-be0a-2b6da012e62f@suse.cz>
Date: Wed, 29 Oct 2025 09:02:00 +0100
From: Vlastimil Babka <vbabka@...e.cz>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
 Andrew Morton <akpm@...ux-foundation.org>
Cc: Suren Baghdasaryan <surenb@...gle.com>,
 "Liam R . Howlett" <Liam.Howlett@...cle.com>,
 Shakeel Butt <shakeel.butt@...ux.dev>, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/vma: small VMA lock cleanups

On 10/24/25 11:09, Lorenzo Stoakes wrote:
> We declare vma_start_read() as a static function in mm/mmap_lock.c, so
> there is no need to provide a stub for !CONFIG_PER_VMA_LOCK.
> 
> __is_vma_write_locked() is declared in a header and should therefore be static
> inline.
> 
> Put parens around (refcnt & VMA_LOCK_OFFSET) in is_vma_writer_only() to make
> precedence clear.
> 
> Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>

Reviewed-by: Vlastimil Babka <vbabka@...e.cz>

> ---
>  include/linux/mmap_lock.h | 7 ++-----
>  1 file changed, 2 insertions(+), 5 deletions(-)
> 
> diff --git a/include/linux/mmap_lock.h b/include/linux/mmap_lock.h
> index 2c9fffa58714..e05da70dc0cb 100644
> --- a/include/linux/mmap_lock.h
> +++ b/include/linux/mmap_lock.h
> @@ -130,7 +130,7 @@ static inline bool is_vma_writer_only(int refcnt)
>  	 * a detached vma happens only in vma_mark_detached() and is a rare
>  	 * case, therefore most of the time there will be no unnecessary wakeup.
>  	 */
> -	return refcnt & VMA_LOCK_OFFSET && refcnt <= VMA_LOCK_OFFSET + 1;
> +	return (refcnt & VMA_LOCK_OFFSET) && refcnt <= VMA_LOCK_OFFSET + 1;
>  }
>  
>  static inline void vma_refcount_put(struct vm_area_struct *vma)
> @@ -183,7 +183,7 @@ static inline void vma_end_read(struct vm_area_struct *vma)
>  }
>  
>  /* WARNING! Can only be used if mmap_lock is expected to be write-locked */
> -static bool __is_vma_write_locked(struct vm_area_struct *vma, unsigned int *mm_lock_seq)
> +static inline bool __is_vma_write_locked(struct vm_area_struct *vma, unsigned int *mm_lock_seq)
>  {
>  	mmap_assert_write_locked(vma->vm_mm);
>  
> @@ -281,9 +281,6 @@ static inline bool mmap_lock_speculate_retry(struct mm_struct *mm, unsigned int
>  	return true;
>  }
>  static inline void vma_lock_init(struct vm_area_struct *vma, bool reset_refcnt) {}
> -static inline struct vm_area_struct *vma_start_read(struct mm_struct *mm,
> -						    struct vm_area_struct *vma)
> -		{ return NULL; }
>  static inline void vma_end_read(struct vm_area_struct *vma) {}
>  static inline void vma_start_write(struct vm_area_struct *vma) {}
>  static inline void vma_assert_write_locked(struct vm_area_struct *vma)