On Mon 09-01-23 12:53:08, Suren Baghdasaryan wrote:
> To keep vma locking correctness when vm_flags are modified, add modifier
> functions to be used whenever flags are updated.
>
> Signed-off-by: Suren Baghdasaryan <sur...@google.com>
> ---
> include/linux/mm.h | 38 ++++++++++++++++++++++++++++++++++++++
> include/linux/mm_types.h | 8 +++++++-
> 2 files changed, 45 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index ec2c4c227d51..35cf0a6cbcc2 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -702,6 +702,44 @@ static inline void vma_init(struct vm_area_struct *vma,
> struct mm_struct *mm)
> vma_init_lock(vma);
> }
>
> +/* 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, unsigned long flags)
> +{
> + WRITE_ONCE(vma->vm_flags, flags);
> +}
Why do we need WRITE_ONCE here? Isn't vma invisible during its
initialization?
> +
> +/* Use when VMA is part of the VMA tree and needs appropriate locking */
> +static inline
> +void reset_vm_flags(struct vm_area_struct *vma, unsigned long flags)
> +{
> + vma_write_lock(vma);
> + init_vm_flags(vma, flags);
> +}
> +
> +static inline
> +void set_vm_flags(struct vm_area_struct *vma, unsigned long flags)
> +{
> + vma_write_lock(vma);
> + vma->vm_flags |= flags;
> +}
> +
> +static inline
> +void clear_vm_flags(struct vm_area_struct *vma, unsigned long flags)
> +{
> + vma_write_lock(vma);
> + vma->vm_flags &= ~flags;
> +}
> +
> +static inline
> +void mod_vm_flags(struct vm_area_struct *vma,
> + unsigned long set, unsigned long clear)
> +{
> + vma_write_lock(vma);
> + vma->vm_flags |= set;
> + vma->vm_flags &= ~clear;
> +}
> +
This is rather unusual pattern. There is no note about locking involved
in the naming and also why is the locking part of this interface in the
first place? I can see reason for access functions to actually check for
lock asserts.
--
Michal Hocko
SUSE Labs
