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>
Acked-by: Mike Rapoport (IBM) <rppt@xxxxxxxxxx>
> ---
> 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,
> --
> 2.39.1
>
--
Sincerely yours,
Mike.
