Re: [PATCH v4 01/10] mmap locking API: initial implementation as rwsem wrappers

[Davidlohr Bueso]

On Tue, 14 Apr 2020, Michel Lespinasse wrote:

> This change wraps the existing mmap_sem related rwsem calls into a new
> mmap locking API. There are two justifications for the new API:
>
> - At first, it provides an easy hooking point to instrument mmap_sem
>  locking latencies independently of any other rwsems.
>
> - In the future, it may be a starting point for replacing the rwsem
>  implementation with a different one, such as range locks.
>
> Signed-off-by: Michel Lespinasse <walken@xxxxxxxxxx>
> Reviewed-by: Daniel Jordan <daniel.m.jordan@xxxxxxxxxx>

Reviewed-by: Davidlohr Bueso <dbueso@xxxxxxx>

With one observation below.

> +static inline void mmap_downgrade_write_lock(struct mm_struct *mm)
> +{
> +	downgrade_write(&mm->mmap_sem);
> +}

Shouldn't this really be just mmap_downgrade_write()? In locking
normally don't add the _lock at the end as it implies the operation
of acquiring the lock.

Thanks,
Davidlohr