Re: [PATCH v4 2/7] mm: introduce vma->vm_flags wrapper functions

[Hyeonggon Yoo]

On Thu, Jan 26, 2023 at 11:37:47AM -0800, Suren Baghdasaryan wrote:
> vm_flags are among VMA attributes which affect decisions like VMA merging
> and splitting. Therefore all vm_flags modifications are performed after
> taking exclusive mmap_lock to prevent vm_flags updates racing with such
> operations. Introduce modifier functions for vm_flags to be used whenever
> flags are updated. This way we can better check and control correct
> locking behavior during these updates.
> 
> Signed-off-by: Suren Baghdasaryan <surenb@xxxxxxxxxx>
> Reviewed-by: Davidlohr Bueso <dave@xxxxxxxxxxxx>
> Acked-by: Michal Hocko <mhocko@xxxxxxxx>
> Acked-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
> ---
>  include/linux/mm.h       | 40 ++++++++++++++++++++++++++++++++++++++++
>  include/linux/mm_types.h | 10 +++++++++-
>  2 files changed, 49 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 8d636e895ee9..abb31103d060 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -627,6 +627,46 @@ static inline void vma_init(struct vm_area_struct *vma, struct mm_struct *mm)
>  	INIT_LIST_HEAD(&vma->anon_vma_chain);
>  }
>  
> +/* Use when VMA is not part of the VMA tree and needs no locking */
> +static inline void vm_flags_init(struct vm_area_struct *vma,
> +				 vm_flags_t flags)
> +{
> +	ACCESS_PRIVATE(vma, __vm_flags) = flags;
> +}
> +
> +/* Use when VMA is part of the VMA tree and modifications need coordination */
> +static inline void vm_flags_reset(struct vm_area_struct *vma,
> +				  vm_flags_t flags)
> +{
> +	mmap_assert_write_locked(vma->vm_mm);
> +	vm_flags_init(vma, flags);
> +}
> +
> +static inline void vm_flags_set(struct vm_area_struct *vma,
> +				vm_flags_t flags)
> +{
> +	mmap_assert_write_locked(vma->vm_mm);
> +	ACCESS_PRIVATE(vma, __vm_flags) |= flags;
> +}
> +
> +static inline void vm_flags_clear(struct vm_area_struct *vma,
> +				  vm_flags_t flags)
> +{
> +	mmap_assert_write_locked(vma->vm_mm);
> +	ACCESS_PRIVATE(vma, __vm_flags) &= ~flags;
> +}
> +
> +/*
> + * Use only when the order of set/clear operations is unimportant, otherwise
> + * use vm_flags_{set|clear} explicitly.
> + */
> +static inline void vm_flags_mod(struct vm_area_struct *vma,
> +				vm_flags_t set, vm_flags_t clear)
> +{
> +	mmap_assert_write_locked(vma->vm_mm);
> +	vm_flags_init(vma, (vma->vm_flags | set) & ~clear);
> +}
> +
>  static inline void vma_set_anonymous(struct vm_area_struct *vma)
>  {
>  	vma->vm_ops = NULL;
> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> index 2d6d790d9bed..da983aedb741 100644
> --- a/include/linux/mm_types.h
> +++ b/include/linux/mm_types.h
> @@ -491,7 +491,15 @@ struct vm_area_struct {
>  	 * See vmf_insert_mixed_prot() for discussion.
>  	 */
>  	pgprot_t vm_page_prot;
> -	unsigned long vm_flags;		/* Flags, see mm.h. */
> +
> +	/*
> +	 * Flags, see mm.h.
> +	 * To modify use vm_flags_{init|reset|set|clear|mod} functions.
> +	 */
> +	union {
> +		const vm_flags_t vm_flags;
> +		vm_flags_t __private __vm_flags;
> +	};
>  
>  	/*
>  	 * For areas with an address space and backing store,

Reviewed-by: Hyeonggon Yoo <42.hyeyoo@xxxxxxxxx>

> -- 
> 2.39.1
> 
>