Date:   Thu, 26 Jan 2023 09:33:45 +0100
From:   Michal Hocko <mhocko@suse.com>
To:     Suren Baghdasaryan <surenb@google.com>
Cc:     akpm@linux-foundation.org, michel@lespinasse.org,
        jglisse@google.com, vbabka@suse.cz, hannes@cmpxchg.org,
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Subject: Re: [PATCH v3 2/7] mm: introduce vma->vm_flags wrapper functions
Message-ID: <Y9I66S6gV2ov9/0F@dhcp22.suse.cz>
References: <20230125233554.153109-1-surenb@google.com>
 <20230125233554.153109-3-surenb@google.com>
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On Wed 25-01-23 15:35:49, 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@google.com>

with or without the proposed renaming (it seems we are not consistent
on that much even in the core kernel - e.g. init_rwsem vs. mutex_init)

Acked-by: Michal Hocko <mhocko@suse.com>

> ---
>  include/linux/mm.h       | 37 +++++++++++++++++++++++++++++++++++++
>  include/linux/mm_types.h | 10 +++++++++-
>  2 files changed, 46 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index c2f62bdce134..bf16ddd544a5 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -627,6 +627,43 @@ 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 init_vm_flags(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 reset_vm_flags(struct vm_area_struct *vma,
> +				  vm_flags_t flags)
> +{
> +	mmap_assert_write_locked(vma->vm_mm);
> +	init_vm_flags(vma, flags);
> +}
> +
> +static inline void set_vm_flags(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 clear_vm_flags(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 mod_vm_flags(struct vm_area_struct *vma,
> +				vm_flags_t set, vm_flags_t clear)
> +{
> +	mmap_assert_write_locked(vma->vm_mm);
> +	ACCESS_PRIVATE(vma, __vm_flags) |= set;
> +	ACCESS_PRIVATE(vma, __vm_flags) &= ~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..bccbd5896850 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 {init|reset|set|clear|mod}_vm_flags() functions.
> +	 */
> +	union {
> +		const vm_flags_t vm_flags;
> +		vm_flags_t __private __vm_flags;
> +	};
>  
>  	/*
>  	 * For areas with an address space and backing store,
> -- 
> 2.39.1

-- 
Michal Hocko
SUSE Labs