Re: [PATCH v8 11/16] mm: replace vm_lock and detached flag with a reference count

[Hillf Danton <hdanton@sina.com>]

On Wed,  8 Jan 2025 18:30:20 -0800 Suren Baghdasaryan <surenb@google.com>
> +
> +static inline void vma_refcount_put(struct vm_area_struct *vma)
> +{
> +	int oldcnt;
> +
> +	if (!__refcount_dec_and_test(&vma->vm_refcnt, &oldcnt)) {
> +		rwsem_release(&vma->vmlock_dep_map, _RET_IP_);

In up_read() rwsem is released reguardless wakeup, which is different
than what is added here. Nit.

> +
> +		if (is_vma_writer_only(oldcnt - 1))
> +			rcuwait_wake_up(&vma->vm_mm->vma_writer_wait);
> +	}
> +}
...
> @@ -735,9 +773,10 @@ static inline bool vma_start_read(struct vm_area_struct *vma)
>  	 * This pairs with RELEASE semantics in vma_end_write_all().
>  	 */
>  	if (unlikely(vma->vm_lock_seq == raw_read_seqcount(&vma->vm_mm->mm_lock_seq))) {
> -		up_read(&vma->vm_lock.lock);
> +		vma_refcount_put(vma);
>  		return false;
>  	}

void up_read(struct rw_semaphore *sem)
{
	rwsem_release(&sem->dep_map, _RET_IP_);
	__up_read(sem);
}